(Topic ID: 321534)

Looking for help on third flash on MPU-200

By wild_pins

31 days ago


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  • Latest reply 10 days ago by Quench
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Added OD lines - RW is for U8 as well (resized).png
U13 behaviour seems to work fine and passes when U8 contains #0 (resized).png
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U8 and U13 not reading out what was written in (resized).jpg
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There are 55 posts in this topic. You are on page 1 of 2.
#1 31 days ago

I was hoping someone may be able to help.

I’ve got issues with getting a third flash on my F2K’s MPU-200 (faulty U8 or U13, the 5101’s).

I did the following things already:
- Removed battery and replaced it with 3xAA and a Diode
- Removed corrosion
- Replaced some components in reset circuitry with visible corrosion damage. Measured Q5 and Q1 via diode check
- Replaced U8 IC socket
- Replaced both 5101 chips with new ones (U8 and U13)
- Confirmed all continuity for U8 and U13 using continuity chart - Repaired traces where continuity was lacking (U8-1 > U13-1, U8-22 > U13-22, C13-Left > U8-22)
- Tested U14 on the board with a diode tester (+ to GND, - to pins) and they all read between +- 0.5 to 1.2)
- Tested with a known good voltage (atx power supply +12V and +5V) -> get 1 flicker, then two flashes.
- Tried booting with and without batteries in battery pack, always flicker & 2 flashes.

I’m reaching the end of the online documentation at this point Any pointers or direction can help!

#2 31 days ago

The 5101= low power ram:
1) 2101 static ram = great for testing mpu board.

#3 31 days ago

Hi vec-tor,

The 2101 is a great suggestion, but they do not seem easy to source here. I will have a look.

Any other things I could check?

#4 31 days ago

Post some clear high resolution pictures of the MPU board showing the repairs.
Did you try using a logic probe to check for signal activity on both of the 5101 chips?

#5 31 days ago
Quoted from Quench:

Post some clear high resolution pictures of the MPU board showing the repairs.
Did you try using a logic probe to check for signal activity on both of the 5101 chips?

Hi, would these pictures do? They show the replaced components and the other shows some trace connections redone with wire

20220902_162744 (resized).jpg20220902_162816 (resized).jpg
#6 31 days ago
Quoted from wild_pins:

Hi, would these pictures do?

At least you have genuine Philips 5101 chips.
Pin 9 of the 5101 in the U13 socket doesn't look right. Please check that the pin isn't bent at right angle under the chip such that it isn't in the socket.

#7 31 days ago
Quoted from Quench:

At least you have genuine Philips 5101 chips.
Pin 9 of the 5101 in the U13 socket doesn't look right. Please check that the pin isn't bent at right angle under the chip such that it isn't in the socket.

I removed U13 and pin 9 was indeed a bit bent. I reseated it correctly and made sure no pins were bent but the problem still persists. I also tried with the third 5101 I ordered but no luck.

#8 30 days ago

Do you have a logic probe or oscilloscope to check for activity on the U8 / U13 pins?

If not you will have to carefully check that there is no short circuits under the new U8 socket pins and note that some signals to U8 come from all over the board. Confirming connectivity between U8 to U13 isn't enough, you need to check from the source (mostly the 6800 CPU) to U8 and U13.

#9 30 days ago
Quoted from Quench:

Do you have a logic probe or oscilloscope to check for activity on the U8 / U13 pins?
If not you will have to carefully check that there is no short circuits under the new U8 socket pins and note that some signals to U8 come from all over the board. Confirming connectivity between U8 to U13 isn't enough, you need to check from the source (mostly the 6800 CPU) to U8 and U13.

I did check the continuity from the 6800 as I assumed that, indeed, was important. However I am unsure how I would go about looking for shorts.

I don't own a probe or scope but am going to buy a logic analyzer so i can hook it up to my PC and see what the communication is doing simultaniously on multiple pins.

#10 29 days ago

check for shorts with a multi meter, do you have one? assuming yes if you've checked for continuity for traces to pins.

on the top of the board, say the 5101 at U8, start at pin 1, bottom left, and go from side to side, so 1 & 2, then 2 & 3, 3 & 4 etc.

except you will have continuity on the pins that have solder pads joined underneath.

if you do have continuity it is likely a solder pad on the top of the board is shorting to an adjacent trace.

even holding up to light, with the 5101 removed it can look okay, but a meter will confirm.

#11 29 days ago

Also have to check for shorts between the pins and the thin traces that run between the pins.

I use an analog multi-meter for this.
Place a meter probe on pin 1 and swipe the other meter probe along all other pins on the chip. If the analog meter dial deflects quickly go back and recheck those pins. Then move onto pin 2 and swipe the other pins. Then pin 3 etc, etc.

Since you used strip sockets for U8, put the board up to a bright light looking for shorts between pins and traces:

MPU_Sockets 004a.jpg

#12 29 days ago
Quoted from Quench:

Also have to check for shorts between the pins and the thin traces that run between the pins.
I use an analog multi-meter for this.
Place a meter probe on pin 1 and swipe the other meter probe along all other pins on the chip. When the analog meter dial deflects quickly go back and recheck those pins. Then move onto pin 2 and swipe the other pins. Then pin 3 etc, etc.
Since you used strip sockets for U8, put the board up to a bright light looking for shorts between pins and traces:
[quoted image]

Thanks for the suggestions, I could not find any shorts between traces.
I also measure the resistance between address pins and they are around 90kOhm, I would have expected open lines.

#13 29 days ago

Do you have an EPROM programmer?

#14 29 days ago
Quoted from Quench:

Do you have an EPROM programmer?

Not at the moment. Are you suspecting faulty roms?

#15 29 days ago

Since you said you had corrosion - I would suspect a broken trace. Take note of the solder job on Quench's board in post #11. Note that he also soldered the pins on the top of the board. This will often fix traces that had damaged through-hole connections. Don't worry about the 90K between pins at this time, I would be more focused on traces which is where I believe your problems are.

With meter - you need to trace all pins that you affected. Start at U8, Pin 1 and follow thru to other pins that use Address Bus A3. Check using your meter at the IC, not on the bottom of the board.
Then move to pin 2, pin 3, etc

Also clean up your solder flux with alcohol and a small, soft brush. Often you can't see some solder bridges until you clean away the old flux.

#16 29 days ago
Quoted from G-P-E:

Since you said you had corrosion - I would suspect a broken trace. Take note of the solder job on Quench's board in post #11. Note that he also soldered the pins on the top of the board. This will often fix traces that had damaged through-hole connections. Don't worry about the 90K between pins at this time, I would be more focused on traces which is where I believe your problems are.
With meter - you need to trace all pins that you affected. Start at U8, Pin 1 and follow thru to other pins that use Address Bus A3. Check using your meter at the IC, not on the bottom of the board.
Then move to pin 2, pin 3, etc
Also clean up your solder flux with alcohol and a small, soft brush. Often you can't see some solder bridges until you clean away the old flux.

Hey GPE, this morning I did just that: cleaned everything with isopropyl 99.9% and went through the continuity charts from pinwiki (https://pinwiki.com/wiki/index.php/Bally/Stern#U8_.26_U13_5101_RAM_Continuity_Chart_for_Stern_MPU-200_Only).

They all measure between 1 Ohm and 1.5 Ohm resistance. Putting my DMM test leads together also gives me a similar resistance, so I assume the continuity is correct.

Will do another check for shorts.

#17 29 days ago
Quoted from wild_pins:

Are you suspecting faulty roms?

I don't think your ROMs are faulty but I could write a quick program ROM to test U8 and U13 separately. But it's probably not worth it since the rework was around U8.

BTW did you check that pins 11 and 12 are connected together at U8?
Can you remove U8 and take some clear photos around the U8 socket so we can see the pin connection soldering on the top side of the board?

I can see the copper pads were not cleaned enough because the solder didn't attach properly to them. I still repair badly corroded MPU boards and can say it is very difficult to get the solder to attach where there was corrosion even after cleaning the copper to a bright color. I always solder tin the copper first to see how well it's sticking and re-clean where necessary before installing components/sockets.

#18 29 days ago
Quoted from Quench:

I don't think your ROMs are faulty but I could write a quick program ROM to test U8 and U13 separately. But it's probably not worth it since the rework was around U8.
BTW did you check that pins 11 and 12 are connected together at U8?
Can you remove U8 and take some clear photos around the U8 socket so we can see the pin connection soldering on the top side of the board?
I can see the copper pads were not cleaned enough because the solder didn't attach properly to them. I still repair badly corroded MPU boards and can say it is very difficult to get the solder to attach where there was corrosion even after cleaning the copper to a bright color. I always solder tin the copper first to see how well it's sticking and re-clean where necessary before installing components/sockets.

Pin11 and Pin12 are connected. I'll take pictures tomorrow.

I did have some solder pads that were getting loose, but I've put them back in place as good as I could. It ain't going to win any beauty prizes because some solder pads have nearly gone, but I did check full continuity from IC legs of U8 and U13 to all connected components: U11, U9, Q5, the EPROMS, etc.. I can confidently say that there is no continuity issue. I've done it now five to six times just because I wanted to be 100% sure. Measured with the IC's in place and on the IC legs, not on PCB traces or solder pads. (assuming that table on pinwiki is complete)

I did a visual inspection of all traces between U8's machine pins and verified nearby pins and pins on other IC's which had traces nearby of other IC's. Nothing popped up. I also tested U8-1 vs every other pin on U8 and U13, then went to U8-2 did the same, etc.. So I have some confidence there are no shorts. Some confidence, not fully confident, though as this is more a hit-and-miss kind of thing.

#19 28 days ago

Was the board booting ok before the corrosion repairs were done?

Can you confirm when you power on, the MPU LED:
Flicker,
Flash,
Flash
and that's it? Just want to make sure you're not counting the power on flicker as a flash.

#20 28 days ago
Quoted from Quench:

Was the board booting ok before the corrosion repairs were done?
Can you confirm when you power on, the MPU LED:
Flicker,
Flash,
Flash
and that's it? Just want to make sure you're not counting the power on flicker as a flash.

Hi Quench,

No, the board was not booting ok before the corrosion repair as well.

I can confirm the flicker, flash, flash and that's it. the flicker is a quick on-off of a few milliseconds or so, the flashes are about half or a full second flashes and that's it.

#21 24 days ago
Quoted from wild_pins:

I was hoping someone may be able to help.
I’ve got issues with getting a third flash on my F2K’s MPU-200 (faulty U8 or U13, the 5101’s).
I did the following things already:
- Removed battery and replaced it with 3xAA and a Diode
- Removed corrosion
- Replaced some components in reset circuitry with visible corrosion damage. Measured Q5 and Q1 via diode check
- Replaced U8 IC socket
- Replaced both 5101 chips with new ones (U8 and U13)
- Confirmed all continuity for U8 and U13 using continuity chart - Repaired traces where continuity was lacking (U8-1 > U13-1, U8-22 > U13-22, C13-Left > U8-22)
- Tested U14 on the board with a diode tester (+ to GND, - to pins) and they all read between +- 0.5 to 1.2)
- Tested with a known good voltage (atx power supply +12V and +5V) -> get 1 flicker, then two flashes.
- Tried booting with and without batteries in battery pack, always flicker & 2 flashes.
I’m reaching the end of the online documentation at this point Any pointers or direction can help!

The 6810 RAM and the 6821 I see are both AMI chips. Change them and any other AMI chips, and see what happens. I don't trust AMI chips at all any more.

#22 24 days ago
Quoted from Gott_Lieb:

The 6810 RAM and the 6821 I see are both AMI chips. Change them and any other AMI chips, and see what happens. I don't trust AMI chips at all any more.

Second that. The gray AMI chips are always the first ones to suspect.

#23 20 days ago

I replaced all the AMI chips without success..

I did some additional stabs at the logic analyzer, and when it is testing U8 and U13, I would assume that it would enable both chips (by setting CE1 and CE2 respectively low and high).

I see CE2 pulsing from time to time, but CE1 remains High, which would mean the U8 and U13 chips never activate.. Since CE1 depends on the states of VUAO2' and address lines A9 and A12, I am starting to suspect the programming ..

how big is the chance that it can pass Flash 1 (ROM) check but still have issues?

#24 20 days ago
Quoted from wild_pins:

how big is the chance that it can pass Flash 1 (ROM) check but still have issues?

Every chance, because the 5101 /CE1 signal is generated by signals not entirely related to the ROMs / U7 RAM.

The 5101 CE2 (Chip Enable 2) should remain high because it's connected to the /RESET signal. The /RESET signal is only active low on power up then it stays high. It should not be pulsing from time to time.

/CE1 should pulse low at the beginning of U8/U13 testing (just after the 2nd LED flash). When the software determines the 5101 has failed they will no longer be accessed/selected so /CE1 will remain high. In other words the /CE1 signal state is only interesting at the start of U8/U13 tests.

If you are saying CE1 never pulses low after the 2nd LED flash then you need to look at the logic gates that generate the signal to /CE1. These start at pins 12, 13 and 11 of U19 then to pins 9 and 8 of U18 and finally pins 9, 10 and 8 respectively of U17. You should see some activity on all of these pins. Maybe you have an open circuit to one of these pins caused by the battery corrosion or U8 socket install.

#25 20 days ago
Quoted from Quench:

Every chance, because the 5101 /CE1 signal is generated by signals not entirely related to the ROMs / U7 RAM.
The 5101 CE2 (Chip Enable 2) should remain high because it's connected to the /RESET signal. The /RESET signal is only active low on power up then it stays high. It should not be pulsing from time to time.
/CE1 should pulse low at the beginning of U8/U13 testing (just after the 2nd LED flash). When the software determines the 5101 has failed they will no longer be accessed/selected so /CE1 will remain high. In other words the /CE1 signal state is only interesting at the start of U8/U13 tests.
If you are saying CE1 never pulses low after the 2nd LED flash then you need to look at the logic gates that generate the signal to /CE1. These start at pins 12, 13 and 11 of U19 then to pins 9 and 8 of U18 and finally pins 9, 10 and 8 respectively of U17. You should see some activity on all of these pins. Maybe you have an open circuit to one of these pins caused by the battery corrosion or U8 socket install.

Oh Sorry, I asked an ambiguous question. I was wondering if there was a chance the ROM check could pass with faulty code in them.

I did check all the logic gates between U9 and /CE1 and CE2 and they all function as expected.

What I noticed when investigating /CE1 was that both U17-9 and U17-10 pulse, but they pulse out of sync, which results in U17-8 always being high. See U17 image attached.
A0 = U17-10
A1 = U17-9
A2 = U17-8
A4 = /CS1 U8

Since U17-9 is based on A9 and A12, i assume those timings are as expected. On U17-9 that seems to be based on the VUA-Q2. I inspected some of the clock signals and saw these timings, see clock signals image. Clock seems to be running at about 813kHz

U17 (resized).jpgclock signals (resized).jpg
#26 19 days ago
Quoted from wild_pins:

I was wondering if there was a chance the ROM check could pass with faulty code in them.

The ROM test adds the value of each ROM location as a sum. At the end of the test, the summation should be zero '00'. Technically speaking there is a 1 in 256 chance a bad ROM could result in the ROM test passing.

Quoted from wild_pins:

What I noticed when investigating /CE1 was that both U17-9 and U17-10 pulse, but they pulse out of sync, which results in U17-8 always being high. See U17 image attached.

In your diagram I see three low going pulses on U17-8 (/CS1).
The first pulse reads the existing value at the lowest U8/U13 RAM location (for backup).
The second pulse writes the test value '01' to the lowest U8/U13 RAM location.
The third pulse reads the test value that was written to lowest U8/U13 RAM location.

The test value read does not match what was written so the program basically halts meaning there was a fault detected with U8 and/or U13.

Now if you have enough analyser probes, I would attach one to each of the four data lines on U8 and the four data lines on U13 and also probe /CS1 as the reference for when U8/U13 are written/read.
You will then be able to see what is written to these RAM chips and what is being read out to see the non-matching data.

#27 19 days ago
Quoted from Quench:

The ROM test adds the value of each ROM location as a sum. At the end of the test, the summation should be zero '00'. Technically speaking there is a 1 in 256 chance a bad ROM could result in the ROM test passing.

In your diagram I see three low going pulses on U17-8 (/CS1).
The first pulse reads the existing value at the lowest U8/U13 RAM location (for backup).
The second pulse writes the test value '01' to the lowest U8/U13 RAM location.
The third pulse reads the test value that was written to lowest U8/U13 RAM location.
The test value read does not match what was written so the program basically halts meaning there was a fault detected with U8 and/or U13.
Now if you have enough analyser probes, I would attach one to each of the four data lines on U8 and the four data lines on U13 and also probe /CS1 as the reference for when U8/U13 are written/read.
You will then be able to see what is written to these RAM chips and what is being read out to see the non-matching data.

That was some excellent advice. I saw the 01 being written, but on the third pulse it outputs just the same thing as what was already in it. See screenshot.

Since these are two new 5101's, did I already fry them or is there something else that would cause a problem with the chip not being able to write? Voltages? slow edges?

U8 and U13 not reading out what was written in (resized).jpg
#28 18 days ago
Quoted from wild_pins:

I saw the 01 being written, but on the third pulse it outputs just the same thing as what was already in it. See screenshot.

Indeed, the diagram down below further illustrates it:

Quoted from wild_pins:

Since these are two new 5101's, did I already fry them or is there something else that would cause a problem with the chip not being able to write? Voltages? slow edges?

I presume the R/W signal you probed was directly at one of the 5101 and not somewhere else? The activity looks correct.

Measure the supply voltage at both of the 5101 chips with the board powered ON - i.e. make sure both the 5101 have power.

Set your multi-meter to DC voltage, place the black meter probe on pin 8 and the red meter probe on pin 22 of the 5101's.
You should measure about 5VDC

MPU200_5101_test_waveformsB.png

#29 18 days ago
Quoted from Quench:

Indeed, the diagram down below further illustrates it:

I presume the R/W signal you probed was directly at one of the 5101 and not somewhere else? The activity looks correct.
Measure the supply voltage at both of the 5101 chips with the board powered ON - i.e. make sure both the 5101 have power.
Set your multi-meter to DC voltage, place the black meter probe on pin 8 and the red meter probe on pin 22 of the 5101's.
You should measure about 5VDC
[quoted image]

The R/W signal is measured at U13 and has continuity to the R/W pin at U8.

DC voltage during test measure around 4.5V whereas after test it moves up to 5V
Checked AC voltage for any ripple and noticed a 0.02V AC ripple on the DC line. Unsure if this is within tolerance.

#30 18 days ago
Quoted from wild_pins:

DC voltage during test measure around 4.5V whereas after test it moves up to 5V

Hmm, 0.5V changes seems unusual. Do you currently have any batteries connected?

You mentioned you already changed both 5101 so it would be strange that the replacements are also faulty.
Do you have any other MPU board you can test them in?

Do you still have the original 5101 and can you redo the data analysis with them?

#31 18 days ago

I don't have any other MPU board (it's my first pinball I am repairing).

I redid the test with the original 5101's in it and the results are less obvious for me.:

analysis of original 5101s (resized).png

update: I swapped the leads on U8 and U13, so I you should read D4 to D7 as D0 to D3 and vica versa. Sorry for the rookie mistake.

#32 18 days ago
Quoted from wild_pins:

update: I swapped the leads on U8 and U13, so I you should read D4 to D7 as D0 to D3 and vica versa. Sorry for the rookie mistake.

Ok, so the first test value of $01 (00000001) passes, the next test value of $02 (00000010) fails.

Can you swap the U8 and U13 chips over at the sockets and redo the tests? Lets see if the results are better.

#33 18 days ago
Quoted from Quench:

Ok, so the first test value of $01 (00000001) passes, the next test value of $02 (00000010) fails.
Can you swap the U8 and U13 chips over at the sockets and redo the tests? Lets see if the results are better.

Hi Quench,

I did the swap and think I got some interesting conclusions.

The result depends on the initial value of the chip socketed in U8. If U8 is #0, (so 0000xxxx as a whole byte) I get a test sequence up to #08 (00001111). After which it fails as it can't as it can't write #10. I tried this for all 4 other 5101 chips I have and none seem to be able to want to write to the chip.

I additionally checked if the RW signal reached the U8 specifically and that did not seem to be the issue. Nor is the OD signal to blame.

I checked continuity on the address lines for both U8 and U13 and they seem fine. No shorts between address lines as well.
Added OD lines - RW is for U8 as well (resized).pngU13 behaviour seems to work fine and passes when U8 contains #0 (resized).png

#34 18 days ago

Where did you get the 5101 chips from? If you flip the chips over do the markings in the plastic look the same? There are lots of fakes and remarked 5101 chips out there. Some are 5101 chips but slower speed chips that may only work reliably in an MPU-100 or Bally board. I’ve also heard that some are 2101 chips or just dead.

#35 18 days ago
Quoted from Robotworkshop:

Where did you get the 5101 chips from? If you flip the chips over do the markings in the plastic look the same? There are lots of fakes and remarked 5101 chips out there.

The ones pictured on the MPU board in the fifth post look original, I've bought heaps from China that look the same with no issues. I also have a box full of Chinese remarks that look very different with a high failure rate.

First picture of real ones with white markings, second picture of units from my fake box with enscribed/brown markings.

PCD5101P_Real.jpg
PCD5101P_Fakes.jpg

#36 18 days ago
Quoted from Quench:

The ones pictured on the MPU board in the fifth post look original, I've bought heaps from China that look the same with no issues. I also have a box full of Chinese remarks that look very different with a high failure rate.
First picture of real ones with white markings, second picture of units from my fake box with enscribed/brown markings.

Any that are laser etched are going to be remarked chips or fakes. May or may not work. I seem to recall getting a batch that did have printed white markings but they were off a bit and ended up being earlier remarked chips. Often that will wear off much easier than the original printing.

From the pictures posted they look like they should be real chips but you never know. There are so many fakes floating around that every chip has to be tested. Can no longer assume a supposedly new chips is good. If they were ordered off ebay from China or from Aliexpress then the likelyhood of fakes goes up a bit.

I just ran into a batch of 20 fake 6802 chips from ebay (all dead) that I had to open a case on.

The memory chips the original poster has may be ok but I had to raise the issue since it is coming up more often and if those were fakes then possibly chasing a board issue that is actually ok.

#37 18 days ago
Quoted from Robotworkshop:

Any that are laser etched are going to be remarked chips or fakes. May or may not work. I seem to recall getting a batch that did have printed white markings but they were off a bit and ended up being earlier remarked chips. Often that will wear off much easier than the original printing.
From the pictures posted they look like they should be real chips but you never know. There are so many fakes floating around that every chip has to be tested. Can no longer assume a supposedly new chips is good. If they were ordered off ebay from China or from Aliexpress then the likelyhood of fakes goes up a bit.
I just ran into a batch of 20 fake 6802 chips from ebay (all dead) that I had to open a case on.
The memory chips the original poster has may be ok but I had to raise the issue since it is coming up more often and if those were fakes then possibly chasing a board issue that is actually ok.

They were bought to a respectable dutch site ministryofpinball.com.. Does this means I need to conclude all my chips are broken and I need to reorder them?

#38 18 days ago
Quoted from wild_pins:

They were bought to a respectable dutch site flippersloop.nl.. Does this means I need to conclude all my chips are broken and I need to reorder them?

They are probably ok then. But had to mention it was a possibility.

#39 18 days ago
Quoted from Robotworkshop:

They are probably ok then.

The corrosion on the MPU board here is actually rather mild - you and I have repaired much worse examples. We've got to be missing something simple..

Quoted from wild_pins:

The result depends on the initial value of the chip socketed in U8. If U8 is #0, (so 0000xxxx as a whole byte) I get a test sequence up to #08 (00001111). After which it fails as it can't as it can't write #10. I tried this for all 4 other 5101 chips I have and none seem to be able to want to write to the chip.

So we can now assume you have confirmed one good 5101 if you can get $00 - $0F data to pass when U8 is $0x?
Can you test all other 5101 chips in U13 and try to get the initial value in U8 at $00 in order to confirm which other chips are good / bad? It seems from the early test results you did have a faulty chip in U13 (where it passed on the value $01 but failed $02).

#40 18 days ago

I ensured that the working 5101 (one of the original ones on the board) was put into U8. Then I tried the other original one as well as the three philips ones I ordered. All four chips present the same issue where what I read out differs from what was written in. I will connect back to the vendor and see what can be done with the faulty 5101s.. Will keep you posted about the further repair. Thank you in assisting me through this challenge.. who would have thought that the new ICs would not work either...

#41 17 days ago

Try a bally ROM or stern m100 ROM if you just want to see if you get past the third flash with just u8

Recommend to get PCD5101P with an original imprint. Date codes would be like mid 80s to mid 90s. Anything with a 2000s+ date code is questionable remark. I bought and resold I think 1000 salvaged pulls of PCD5101P about ten years ago and had like less ten or so dead and I never had one go bad on me once in service that I have heard about. I think someone mentioned PCD5101P brand has clamp diodes that most of the others do not. For whatever reason this 5101 memory has extremely high fail mode. When I did PCB repair dead 5101s was super common. I am not sure if it is ESD that kills them or what. But every brand, WMS, Stern, Bally, and Gottlieb boards all had bad 5101 too often.

Also check the stupid 12v to 5v circuit they use to power the RAM. Very often to find that voltage clocking in at like 5.5vdc and higher.

#42 17 days ago

5101's are extremely sensitive to static discharge. Philips was the last manufacturer of 5101s and I think Andrew is correct about clamping diodes on the interface pins.
One thing the chinese have not figured out on blacktopping and remarking: tooling holes on the top of ICs. If the tool holes are clear and shiny then they are most probably real. If the tooling holes are rough then they *might* be fakes but there are some real parts that have rough tooling holes. Your image in post #5 - the PCD5101s look legit.
Quenches images from post 35 have some interesting parts. First set (the ones he said are legit) have nice, shiney tooling holes on top. Yes, i would agree they are legit.
The remainder look awful. Especially the third set where you can see the direction the sander went when removing old numbers. Some are marked with 5101 variations on the bottom. They were probably 5101s to begin with but were handled so roughly during removal that they probably didn't survive. The 5101E parts look to be oldies from RCA.
An example of how china gets a lot of their 'new' parts:

#43 17 days ago

While I'm waiting on new 5101s, I was looking at the board and noticed at least two tantalums.. Do you reckon I should change these as well. If I recall, these go bad as well after a while..

#44 17 days ago
Quoted from wild_pins:

While I'm waiting on new 5101s, I was looking at the board and noticed at least two tantalums.. Do you reckon I should change these as well. If I recall, these go bad as well after a while..

Only time I change them is when they've broken off. 35V Tantalums are usually used here and they're on the 5V supply rail so there is plenty of margin for the breakdown voltage. Don't think I've ever had one fail on a MPU board.
But it's up to you.

#45 17 days ago
Quoted from G-P-E:

5101's are extremely sensitive to static discharge. Philips was the last manufacturer of 5101s and I think Andrew is correct about clamping diodes on the interface pins.
One thing the chinese have not figured out on blacktopping and remarking: tooling holes on the top of ICs. If the tool holes are clear and shiny then they are most probably real. If the tooling holes are rough then they *might* be fakes but there are some real parts that have rough tooling holes. Your image in post #5 - the PCD5101s look legit.
Quenches images from post 35 have some interesting parts. First set (the ones he said are legit) have nice, shiney tooling holes on top. Yes, i would agree they are legit.
The remainder look awful. Especially the third set where you can see the direction the sander went when removing old numbers. Some are marked with 5101 variations on the bottom. They were probably 5101s to begin with but were handled so roughly during removal that they probably didn't survive. The 5101E parts look to be oldies from RCA.
An example of how china gets a lot of their 'new' parts:

I don't think they recycle chips anymore like this. There are some dump sites in Shenzhen that look like this though.

I have seen videos of a multi million dollar high tech factory in china that all it does is salvage chips from pallets of E-waste for them to be sold back into the market. They can stamp on new legs to chips, Pull them cleanly, probably laser etch, and everything. I wouldn't be surprised if you bought brand X transistor from LCSC and took it too this company they would change it to whatever your favorite western brand you want. They have a process that can hide all the scuff marks on used but not remarks pretty well, if you rub a chip with acetone it will expose all the scratches from the boards being stacked on pallets 10ft tall.

I am sure very little testing goes on, but they will erase EPROMs they salvage. They will even write NVRAM chips back to all 00 so it looks like a new chip.

#46 17 days ago

These are all genuine. Around 1990 dated and later should have a printed vertical bar on the left side and the Phillips shield logo.

I don't have a ton of examples left, but each one that has "kfm" also has "Korea" stamped into one of the bottom side tooling holes. "mfm" ones do not. Tooling marks are all similar to the same. Except the mfm ones do not have a country stamped on the bottom. M for Malaysia? The other tooling hole has a one or two digit number.

20220916_172904 (resized).jpg
20220916_173652 (resized).jpg

#47 17 days ago

Those used to be quite easy to find but supplies have long dried up. Philips made fast and reliable parts.
The right two from 1987 were probably made before Philips finished changing the branding from Signetics to Philips - it only took them 12 years to accomplish this.

Oh - and the chinese don't laser etch remarked parts. They actually use a brownish colored ink that only looks like its laser etched. I remember when Texas Instruments started laser etching parts. 'This will bring an end to all counterfeiting!' Well, no it didn't. Hold up a brown ink part to a laser etched part - to the naked eye, you cannot tell a difference.

#48 16 days ago

I bought some PCD5101s from China where the seller had pics of 100% genuine chips on the listing & no reports of blacktopping/fakes or remarks parts in their feedback, also they were more expensive.

I received remarked parts, so it's a gamble regardless buying this way. The first thing I did was look underneath the chip to look for the shiny borders running along the sides to identify the chip - all the later chips with the Philips logo I have seen have these very narrow shiny borders with a rounded edge on the top & bottom as seen in the pic below. At least I knew if they then worked they were the correct PCD5101s.

Remarked part on the left & genuine on the right.
IMG_1974 (resized).JPGIMG_1970 (resized).JPG

#49 11 days ago

Small update, I've been waiting for new 5101. This time I thought I'd try from my local electronics store.. took about a week to get them in the shop... picked them up today and they were branded "PCD 5101AP".. Other markings are "MRM8231 2 Y" and at the bottom "21655".

Can't find a datasheet, though.. and some sites refer to the manufacturer as "Sig", though no manufacturer is on the chip .. will give it a go tomorrow and see what it does, but my hopes are not that high.

#50 11 days ago
Quoted from wild_pins:

Other markings are "MRM8231

Manufacture date: 31st week of 1982

Quoted from wild_pins:

and some sites refer to the manufacturer as "Sig"

Probably short for Signetics. Philips bought Signetics which might also explain the early date code.

Post pictures of the chips when you get them.

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