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!

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?

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

20220902_162744 (resized).jpg

20220902_162816 (resized).jpg

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.

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.

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.

Not at the moment. Are you suspecting faulty roms?

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.

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.

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.

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?

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).jpg

clock signals (resized).jpg

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

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.

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.

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

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?

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...

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..

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.

Got them, see attachment

20220922_221558 (resized).jpg

They do! Six flashes on the bench! now I can continue with testing everything else. But first will double check if all the voltages coming in are good enough before I plug in the board in the pin.

Thank you so much everyone in helping me better understand this board and guiding me through the process. I feel I better understand it now and will be much more able to debug the next thing that comes my way.