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Sys11 U10 PIA error on boot, sometimes...

David_Vi

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We grabbed a new (refurbed) sys11 MPU board last minute to get DINER working for Pinfest.
Major thanks to the Pinfest NLP guys and @pinballmania to swapping the board in and assisting with the errors.

The issue is, most of the time it doesn't boot up, you get the WPC test bong noise and U10 PIA failure. If you turn off and on a few times the game boots but instead of the test bong you get a sound effect from the game, which is not expected behaviour. The old board and my other sys11 does the test bong on every boot.

Andy and NLP guys seem to think it's the u10 socket, it could be dirty ? If U10 itself has failed or has issues would it still boot intermittently?

We got the board from @BrianSoton and he's been great. It tested and worked fine on his test rig and his own game and is happy to have it back to look at and attempt to resolve. But if it's something simple or cheaper than the postage to send back I may as well have a go. Plus I'm less likely to lose all the great high score from the players at Pinfest if I take a look at home as it still has batteries.

diner is a SYS11C Game but the board isn't a 11C, not sure which it is but it has the sound area populated. I'm not sure if that's an issue.

We are taking Diner to the UK Open in 3 weeks so would be good to solve this before then.

Is it worth trying a replacement 6812 IC? Where can I get them, Andy is out of stock and I need a couple anyway. eBay only seems to have ones that ship internationally. Unless there's an equivalent more easy to find IC I could use instead?
 
Worth looking here for PIAs: https://www.pinball.center/en/shop/electronics-parts/ic/1160/68b21-pia/6821-mc68b21p

These guys are good and I just got a load of plastics for my Banzai from them. Cheap enough to get a couple for test purposes.

Have you checked the socket for cleanliness? Is the board itself OK - test from socket to somewhere else at the other end of the trace for good continuity? eg hidden battery damage?
 
Worth looking here for PIAs: https://www.pinball.center/en/shop/electronics-parts/ic/1160/68b21-pia/6821-mc68b21p

These guys are good and I just got a load of plastics for my Banzai from them. Cheap enough to get a couple for test purposes.

Have you checked the socket for cleanliness? Is the board itself OK - test from socket to somewhere else at the other end of the trace for good continuity? eg hidden battery damage?

I've tried new ICs and same result. The board was fully tested by the guy we bought it from and was working fine before getting to Pinfest.

We've got the orginal board fixed so we'll be taking the new one out and can look at the socket properly.

The seller has been great and is happy to take it back and take a look.
 
Ah OK wasn't sure if you were still looking for a source for new ICs. Sounds like a board problem then. Fingers crossed it all gets fixed, sounds like the seller is standing behind it at least. Good news.
 
Ah OK wasn't sure if you were still looking for a source for new ICs. Sounds like a board problem then. Fingers crossed it all gets fixed, sounds like the seller is standing behind it at least. Good news.

Yeah he's been great. Offered to send a replacement too.
We don't need two boards now we've got the old one fixed but I suppose it's always good to have spares as these sys11 boards are incredibly hard to find now.
 
Yeah he's been great. Offered to send a replacement too.
We don't need two boards now we've got the old one fixed but I suppose it's always good to have spares as these sys11 boards are incredibly hard to find now.
Yes definitely. It’s repair or Rottendog really.
 
Dear all,

I want to add latest information to that U10 PIA FAILURE, which occurs by chance when switching on a Williams SYSTEM 11 after a longer period (hours or days).

All details are mentioned in the thread above, but lets have a summary:
The Pinball starts with U10 PIA FAILURE randomly. Instant switching on and off does not bring the failure back. It does show that at the very first power on only.
If you look for exactly that behaviour, continue to read. If not, you may have to fix other issues.

I claim to finally have a solution, tested on my 1987 BIG GUNS.

Technical background:
If you have searched carefully the internet for that kind of failure, I may assume all other proposals have been tested by you already?
  • you are sure to have +4.95...5.05V tested, being on PCB CPU
  • you have replaced C7 & C8 (Greinacher voltage doubler) on PCB POWER
  • you have checked the complete PCB CPU RESET section (also see commented cutout) and also have replaced C30 by a new 47u?
... but nothig has helped yet?

I have noticed a short buzz tone, sometimes a sizzle noise instead, brought by the PCB SOUND, whenever I power on the pinball. I´m pretty sure some of your W11-Machines do the same.
It was that buzz/sizzle which let me look closer to the schematics.
U10 is the PIA which is controlling the sound board via the ribbon cable. Why should U10 send any signal before getting a RESET? And why occurs U10 PIA FAILURE only after a longer period of being powered down?

The linear controller uA 723 regulates a precise 5.0V down from an unregulated +12V.
The Greinacher voltage doubler (D1, D5, C7, C8) works fine as long as fuse F5 is okay. If F5 fails, the Greinacher will be cutted off from the 12V AC, which leads to a loss of supply at pin 11/12 on uA723. Instantly the 5V go down and the CPU stops by being resetted. This for safety reasons - otherwise the transformer would run on the half winding... not good.

Referring to the original datasheet of TexasInstruments ua723 (here: ) at page 5, a capacitor is recommended, connected in parallel to "R2".
Looking in Williams' schematics, there is no such capacitor.

This is a filter capacitor, helping to have a smooth output voltage. If you use a larger capacitor, the ua723 ramps up the +5.0V slowly.
Remember: The Greinacher needs some full AC swings to bring C8 up to 25 volts - some hundreds of milliseconds. The RESET section itself holds around 100ms to release /RESET.
I guessed it may jam occassionally when /RESET keeps low not long enough and/or +5.0V is not precisely regulated during the first few 100 milliseconds!

I have added a 10uF/50V electrolyt capacitor in parallel to Resistor "R8" on PCB POWER. That was easy, because a space is kept free for it. See picture. Ensure polarity! (+) to the left, (-) shows in the direction of the heatsink.
Result: No beep or sizzle when powering on anymore - the reset works well and U10 has plenty of time to raise all its guts, before /RESET may release and start the test program.
Together with the disappearing of buzz or sizzle, also the U10 PIA FAILURE is history, at least in my BIG GUNS.

I appreciate any comments.

Regards, Molzen
 

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Brilliant info thank you!! Had a P10 just the other day but it cleared on reboot. Thank you for this forensic analysis on why!!
 
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