Finally got around to rebuilding a board I picked up off Ebay a few years ago. Got it all working on my bench, so decided to give it a real test in my Flash and it runs at almost double speed. Attract mode lights run fast, end of ball bonus count off is fast, everything is fast.
Swapped clock crystal, CPU IC, PIA from good board. No change. Has anyone ever seen this condition?
I'm too lazy to fish out schematics, but is there a clock divider circuit on that board?
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Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info
Is it definitely a system 6, or perhaps a system 4?
No clock divider that I can think of, crystal goes straight to the CPU with just smoothing caps on it. Have you changed the capacitors?
When you changed the CPU, any chance you put in a 68000 series chip instead of a 6800?
-Hans
Quoted from HHaase:Is it definitely a system 6, or perhaps a system 4?
No clock divider that I can think of, crystal goes straight to the CPU with just smoothing caps on it. Have you changed the capacitors?
When you changed the CPU, any chance you put in a 68000 series chip instead of a 6800?
It is a 6. I have not changed the caps yet. CPU is the right one from a properly working board.
Could those caps really effect the speed? I'll have to pull them from the good board.
Oh, bye the way, I'm using a set of your tools to work on these and I love them 
CPU.jpgThose caps won't affect the speed. Those are noise filtering caps.
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Chris Hibler - CARGPB #31
http://www.Team-EM.com
http://webpages.charter.net/chibler/Pinball/index.htm
http://www.PinWiki.com - The Place to go for Pinball Repair Info
WMS started using the 6808/6802 CPU at sys 6. It has built in clock circuitry compared to sys 3 and 4 that use a 6800 cpu and a clock generator ic.
Measure the speed of the clock. P37 of the CPU. Sys 6 runs around 900 KHz. DMM with frequency counter or scope would be needed.
Try a new 6808 cpu but it is probably the crystal if the clock is off. I have seen them run slow and fast.
If the clock is good check the IRQ? Maybe the CPU is getting slammed with request out of frequency. I am guessing it will look similar to the "E" clock
How about the IRQ at the PIA, P37&P38? That goes through a different logic gate than the IRQ test point.
All timing of things is from the clock counting and triggering an interrupt in a WMS game from what i can gather. Not like a bally where there is the zero crossing timer or display timer circuit.
Finally got back on this mess. Re-checked the readings. I think the easy hook attachment on my probe was picking up noise from the board as the IRQ readings are now a bit different.
TP6 BUS is still the same for both boards at 894KHz
IRQ on good board is around 980KHz, fast board around 600KHz
IRQ at the PIA on good board is around 1.3MHz, fast board around 1.5MHz
When the theory starts getting this deep i narrow down the most likely issues and check pin by pin vs known good.
My best guess is somewhere in IC5, IC25, IC11
Quoted from barakandl:When the theory starts getting this deep i narrow down the most likely issues and check pin by pin vs known good.
Kind of figured it would lead to this. I'm surprised that this board is running at all as someone had already been working on it and their soldering was terrible. Had to replace sockets that had already been replaced, etc... Triple checked continuity everywhere. This will be a good winter project.
Finally got back on this tonight. With both boards running Andre's test ROM side by side on the bench, started checking voltages on IC25 and discovered 2.3v missing on pin 14 which is directly connected to IC11 pin 11. Unsoldered pin 11, still no 2.3v at IC25-14. Decided since one pin is already unsoldered might as well socket & change IC11. Fired board up and now have 2.3v at IC25-14. Installed board in machine and is now running at normal speed.
Thank you barakandl, good call! 
That was an odd one. Good find!
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Chris Hibler - CARGPB #31
http://www.Team-EM.com
http:/webpages.charter.net/Hibler/Pinball/index.htm
htp://www.PinWiki.com - The Place to go for Pinball Repair Info
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