6502.org

Hello,

I have been roped into fixing my friends Pinball machine.

It is 6502-based, has 2 RAM chips (not sure what they are but they're about the physical size of a 6116), 2 PROMs, 3 6532s and a battery backed 5101 RAM for factory settings and hi scores.

The PROMs are socketed but everything else is soldered.

I'm going to CRC check the PROMs first, and assuming they are OK, the next step is to pull the 6502, solder in a socket and get my Fluke 9010A on it. (As shown here http://artsarcadegames.com/fluke_9010.htm)

I can test ROMs and RAMs easily, and my hunch says that it's a RAM problem (often is with old arcade games) but I've never tested a board with 6532s before. Do these often fail? Can anyone tell me how they occupy the address space or point me at a datasheet?

If one of these is blown, is there much chance of it stiffing the rest of the CPU system by holding a line high or something?

What I'm really trying to do is get this fixed with as few visits to my friends place as possible as it's right in the centre of London, and thus be armed with knowledge. Fixing pinball PCBs is awkward as they are at the top of the machine and have lots of connectors on them!

Thanks,

Actually, those two are NOT RAM chips, but are 741542, whicih are 4 to 16 line covertors.

The RAM is located within the 3 6532s. They also serve as port chips.

First thing to check, if you have the battery, remove the bugger. If it leaks, it can kill the board for good. Check for corrosion. If you have thta, you will have to rewire traces, plain and simple.

Check your reset and clock lines. Also, check your /IRQ. If its low, one of the 6532s went bad. This is common.

Are you getting any form of activity on the clock or data registers?

Also, you have about 10K of program, the two 24 pin chips next to the 6532 are actually the BIOS mask roms. Those alos fail.


If you cannot get it, you can send it to my job, and I will end up fixing it. We do fix reasonably and have warranty. If its unfixable, the price is greater due to full board replacement.

Right, so those chips are not RAMs then. I wondered why I didn't recognise the numbers on them. I was surprised also that it would need so much RAM, as there can't be much to store for a pinball machine!

The machine does have a little corrosion, but from what I could see on my brief look, the only components that are close are a few resistors that feed some output transistors, so they shouldn't stop it running. I'll buzz them anyway. I've already removed the battery and 5101 but that didn't allow it to boot. (Apparently you can boot the board with it removed.)

I didn't have a logic probe with me at the time so couldn't check for simple stuff like dead clock.

Looks like 6532s might be the next major thing to check. Anyone have any thoughts on how they appear in the memory space?

You've probably checked this already, but I'll mention it anyway. Check the power supplies first of all! I've seen several cases of tantalum decoupling capacitors that fail by going short-circuit across the power rails.

After that, as you mention, check clock signals and the like, then start looking at the 6502's bus with the logic analyser. Having said that, I found a faulty PROM chip in a PDP-11 by spraying it with freezer spray (it failed only when hot).

Do let us know how you get on!

> Anyone have any thoughts on how they appear in the memory space?

The data sheet can be found by going to http://www.6502.org/documents/datasheets/mos/ , and clicking on the 6532 line about 7th from the bottom.

The 6532 has 7 address lines and a RS (register select). RAM is accessed with RS low, and the I/O and timer and control and status register with the RS high. Since you pretty much have to have RAM in pages 0 and 1, I expect they put one 6532 in each of those pages.

If oyu have corrosion, the traqnsistors are the reset circuitry. That means your reset and possibly clock went bye bye.

gopt the memory map around of that board, forgot where it is though, will post it sometime.

OK, I've tracked down a load more information regarding this PCB and will be having a go at it tomorrow.

I'm hopeful it will be just corrosion where the battery was (removed it on my last visit).

I don't hope it's a 6532 problem, as I don't have any spares and they're all soldered in!

Will post again when there's an update.

Fixed. I humped my fluke, scope, EPROM programmer, spares, Logic Comparitor and some spares all the way into London only to find no clock to the processor.

After tracing the problem to an acid damaged track under the battery, and fixing that, the board ran OK. I also needed to replace a load of the 7-segment display driver logic.

Thanks your words of encouragement!

Phil