(Topic ID: 287358)

WPC-98 Cap ID please

By darowla

8 months ago


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  • Latest reply 6 months ago by G-P-E
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Bad Clocks (resized).png
32KHz Clock Signal (resized).png
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#1 8 months ago

HI,
I been doing a clean up job and I took these small caps out C29, C30. According to the book they are 22PF 1KV Radial's - well I get ceramics if I go searching but should I replace them with ceramics.

What would u repalce them with? They now snapped due to the poison on the board.

Thanks

IMG_2063 (resized).JPG
#2 8 months ago

Definitely ceramics here.
22pF ceramics as part of your 32.768kHz clock circuit.
These do not need to be super accurate but I would stick with C0G (stable) rated caps.
Nor do they need to be rated for a whopping 1kV. Anything 10V or higher will work.
Axials are sometimes not as easy to find as radial style, radials will also work but won't have the same 'fit'.

Either of these will work but the Axial will fit better:
Axial = Kemet C410C220J2G
Radial = Vishay K220J15C0G

#3 8 months ago

thank you
Going thru that area, scoping also gave me crazy results and thought I would try and tidy that side up. Currently got a non-booting (two top and bottom LEDs on only) setup.

#4 8 months ago
Quoted from darowla:

thank you
Going thru that area, scoping also gave me crazy results and thought I would try and tidy that side up. Currently got a non-booting (two top and bottom LEDs on only) setup.

I built a wpc89 MPU without the RTC stuff installed and it ran fine, so these are not likely the cause of a total lock up

#5 8 months ago
Quoted from darowla:

What would u repalce them with?

This is a complete WPC89 parts list I made MANY years ago ... some parts may no longer be available.
https://docs.google.com/spreadsheets/d/1C4znEqZd4K4eywhi__qDwI-3AsX6Y5qdw9Pzb0p178A/edit#gid=1430569459

It contains links, costs, units per assembly for every part on the board from Mouser Electronics. ... I would be happy to add links to G-P-E parts if you would provide them to me.

I put this together mainly for my self for supply acquisition and record keeping as I already had ALL of this information available from manufacturing a few boards.

#6 8 months ago

There is a lot of corrosion throughout the area that you show in the picture. Can you post a picture of the whole board?

#7 8 months ago

hi yes corrosion in a lot areas, slowly going thru it all, I think game was stored on it's side. Thanks for the further replies, I have ordered matching axial caps and few crystals, I just want to see a decent 32khz signal on my scope but understand that its not needed from replies above, I ordered a NVRAM to replace the the battery set.

The story is game played for one session before it died, so I studied it and took it back home and put it on the bench. I am recording my progress for a video later.

I think I order some more parts from the sheet, I dont have that many swaps, I did swap for a known working 6809. I did probe around and there is barely any movement on two pins that has activity. The schematic doesn't have any high signals on it, so that didn't help and the 6809 is not even on it.

I get back to it in a few days and report in.

#8 8 months ago
Quoted from darowla:

I just want to see a decent 32khz signal on my scope

The Yellow trace is from a board built using ALL new components as listed in the parts spreadsheet; the Cyan trace is from a fully functional WPC089 board mfg in 1992.
32KHz Clock Signal (resized).png

#9 8 months ago
Quoted from darowla:

thank you
Going thru that area, scoping also gave me crazy results.

Seems like the probes can crash out crystal oscillator circuits like these. Parasitic capacitance?

I am not sure if it is exists with this RTC but usually look for an external clock on the CPU. It is a better place to check if the clock is working.

#10 8 months ago
Quoted from barakandl:

I am not sure if it is exists with this RTC but usually look for an external clock on the CPU. It is a better place to check if the clock is working.

There is no external clock for this; this is nothing more than a clock frequency for the real time clock (RTC), the processor itself doesn't care if it there at all, fast, or slow...it only controls the rate at which the clock keeps time...if you make this a 64KHz clock your game will play fine but the RTC will run twice as fast.

I actually tested this for someone who has a wrong resister installed in the RTC circuit; those clocks looked like the yellow waveform shown below in Channel 1 compared to a the correct 32KHz clocks stored in memory (Green Channel).

Bad Clocks (resized).png

This frequency was very unstable as the RTC circuit was not designed to operate at this frequency.

pasted_image (resized).png

#11 8 months ago

In this case it is all external. With the CPU chips like a 6802 U21F gate is built into the CPU chip. Probe at U21 P12 for clock pulse would be a safe place. If you stick the probe around C29 and C30 is where you may crash out the crystal and it stops oscillating.

3 weeks later
#12 7 months ago

hi, ended up putting some replacement parts in that area, ended up with a different xtal that rated at 32.768 Khz but scope is now givinig a strage sine wave are 1.5Mhz... The over message said it is not critical so i will leave it for now.

My Boot doesn't happen, if I remove all chips the Top and Bottom lights remain the same, regardless of Watchdog.

My next goal is to tackle the ASIC, if I remove that I get 3 lights on start-up.

The Asic has had small amount of corrosion, I haven't considered it a 'right off yet'. I ordered a different socket as I seen pins not gripping very well so thats my next move.

This ASIC, I seen it for sale by some pinball repair sites, I presume its programmed or custom made in some way?

I been studying around the processor, seeing what it needs, I have now got some activity on the data/address lines, so I made some progress

1 week later
#13 7 months ago
Quoted from darowla:

hi, ended up putting some replacement parts in that area, ended up with a different xtal that rated at 32.768 Khz but scope is now givinig a strage sine wave are 1.5Mhz... The over message said it is not critical so i will leave it for now.
My Boot doesn't happen, if I remove all chips the Top and Bottom lights remain the same, regardless of Watchdog.
My next goal is to tackle the ASIC, if I remove that I get 3 lights on start-up.
The Asic has had small amount of corrosion, I haven't considered it a 'right off yet'. I ordered a different socket as I seen pins not gripping very well so thats my next move.
This ASIC, I seen it for sale by some pinball repair sites, I presume its programmed or custom made in some way?
I been studying around the processor, seeing what it needs, I have now got some activity on the data/address lines, so I made some progress

The ASIC is a special, custom made chip but it does not need to be programmed. Hopefully it is just ASIC socket.

I would expect to see the 32 khz at U21 P12 like Pin_Guy posted above. Maybe check it again while you have the ASIC out of the board.

#14 6 months ago

hi the new socket arrived for the ASIC, which will happen. I am now just tracing around seeing what other faults I can find, also just wanted to know more about what the ASIC is actually doing? Does it control Blanking?

I have found a broken trace affecting A2 which I will be dealing with, although it under another socket so it could have been me. I taken most of the important chips out and just measuring around to see what's left to do.

#15 6 months ago

I have seen this become an issue on PLCCs many times:
https://www.greatplainselectronics.com/Information.asp?region=139

Often manifests itself as a bad ASIC or bad socket.

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