The CPU at U9 may get a bit warm, but the 6810 ram at u7 does not typically heat up much in operation. That might be a clue to try a new one.
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Just to keep in mind my replacement MPU does not use 12v for anything. The stock MPU uses 12v to make the reset, diag led, and powers u8 ram.
Quoted from JT-Pinball:At this point I think your transformer and rectifier are probably good. The lm323 5V regulator in the SDB has a tollarance of 1%. This means the voltage on TP1 and 3 if tied together should be no greater that 5.05V. Has any other work been done to the driver board?
not when Bally wires up the LM323K like they did. They are usually putting out around 5.25vdc in that setup.
Quoted from spiroagnew:Thanks for the discussion to help me follow through on this. So...
Repro MPU: Doesn't use 12v. Works in the game.
Original MPU: Uses 12v for RAM (among other things). Constant resets. U7 RAM is getting hot, while operating at 5.24VDC.
So my next plan of attack be to look at the 12v/5v line from SDB to MPU?
sounds good. you could have a flaky 12v connector causing the reset to drop out or the the ram to undervolt and mess lock up the system. my replacement MPU seemingly would use quite a bit a less current than the original too making a marginal connector less likely to cause a problem.
when it is hot and locked up I'd check some signals. See if the clock stops pulsing in time (P3 and P37). See if the vua-q2 stops pulsing. Since u7 heats up check the unique chip select, (i think it is /a9?). Check the 12v test point and the reset. If the zero cross input to the pia stop pulsing could indicate a problem with u14. I think you said u14 heats up too, really shoundt unless the 82 ohm 2w resistor is baking it from below.
Make sure you didnt tear out the ground pins at J4 when redoing the headers. The ground return comes in on the topside of the pcb only (bad original design). You see a lot of people run a jumper wire from J4 ground pins to the outside of pcb ground area.
using the u7 chip leg's vcc and ground connection check resistance to ground and 5v spots on the board looking for excessive resistance. milliohm dmm is nice here.
Quoted from srcdube:Looking at the schematic on this... ignore comment above about regarding harness wires, since this is in the middle of the board. As RAM there are no output signals that this chip alone drives... everything is shared busses. So what would make this chip drive more current than it should, but it still works OK for some time?
Address bits 17-23 are all inputs only, so not likely a problem.
R/W line pin 16... not likely the problem. If it was stuck, other chips wouldn't work.
Data bits pins 2-9... if any of the other devices on the databus are not tristating correctly, or there are some resistive paths to ground it could draw more current from the RAM. With power off check the resistances to ground on those pins. However I expect if there was a bus problem like that, then more chips on that bus would have problems, not just the RAM?
Chip Select Pins 10-15... if something is wrong with those signals, particularly stuff that decodes only to that RAM, then the RAM may be incorrectly trying to drive the data bus when other chips are driving the data bus at the same time. U18 pin 15?
would think /a9 problem would show up elsewhere, but maybe not since how the other CS for the 6810 are wired. compare the /a9 pulse (inversion of) A9 or if you have another working MPU if you have one handy compare to that. *note my replacement board does not use /a9 so it can support access larger ram/rom space, so can't compare exactly to it*
check compare vua+clock phase 2 as well to a working board too
Quoted from spiroagnew:I tried to look at this last night. I measured the resistance of the ground/5V from U7 to the other ground/5V points on all the other chips. The only non-Zero readings I got were to U9. But I tested the same points for resistance on another Bally MPU and got the same readings. So I'm not sure this is the issue. Are there other specific non-chip components in line with U7 I should be testing?
I had the game playing for quite some time last evening, about half hour, with no freezing. U7 still got warm, but it didn't lock up. However, when I turned it off and then on again, the LED stayed lit and needed to cool off before it could get its seven flashes again.
Swap u15, u17 and u19 for sanity sake and since your handy at desoldering. That should cover the rest of the gates that triggers u7. U15 goes out the most often as it is driven really hard. Can use 7437.
Quoted from Quench:Yes sounds like you have a problem in the reset circuit. You can add the capacitor as per Clays guide but that's only masking a problem.
What's the voltage across zener diode VR1 (in the reset section) on the MPU board?
Have you run this board on the bench to see if U7 still gets hot? When you say hot, can or can't you leave your finger on it?
Your picture shows a Fairchild brand 6810 at U7 - are the other 6810 you've used also Fairchilds? I've just put a Stern MPU-100 board on the bench with a Fairchild 6810. After 10 minutes the chip gets warm (in free air). It's certainly not too hot to touch, but it's not cool either.
.Not really. BTW, what happens if you put this board into one of your other Bally machines?
Can you also amuse me and remove the coin battery. Does the board still fail with a locked LED when warm?
if i recall I remember reading clay's guide says to use 470uF or something to extend the reset delay. That cap is about 10x too large of value. I played around with it once and I think I got a 1uF ceramic cap to greatly extend the reset delay. I don't think this is your fix and I would bodge in a MCP-130-460 reset device before doing the cap trick. You can put the MCP-130-460 across the legs at u9 on the back of the board and then can cut out most of the reset crap in the bottom left corner. The reset chip connects just the +5v, gnd and reset.
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