Hello everyone,

to be honest I am not very familiar with the mpus in question, but please allow the maybe stupid question...

I have a pcb using a 6503 which seems not to be working. As I do not find a source with acceptable pricing it came to my mind to double check the properties/ datasheet of an 6502 in comparison to a 6503. If I would create a piggy-back to adapt the necessary pins and keep the remaining unconnected, would this work?

Thank you in advance for a short feedback Mark

You could probably design a 28-pin to 40-pin adapter and since the 6503 can be considered a subset of the 65C02 it should work just fine. Unless of course the software for the 6503 took advantage fo some of the undocumented "features".

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Bill

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x86?  We ain't got no x86.  We don't NEED no stinking x86!

Visual inspection is the quickest and most effective way to find faults. It is the first step in troubleshooting especially with boards that were known to be working previously. When visual inspection didn't find the fault, my own experiences, after spent many many hours troubleshooting with scope and logic analyzer, invariably showed mechanical faults that were either hidden or something I didn't look for initially.
Bill

Indeed.

Can you supply more info about this "pcb using a 6503," Mark? Photos would be helpful, as well as a more detailed description of why it seems not to be working. (Photos can be attached with your post.)

-- Jeff

ps - welcome!

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

Thank you all for the warm welcome

Yes, I have a Digital-Volt-Meter and Logic-Tester available.

Just some background to my pcb in question.... The board is a sound card (C-19389) from a Gottlieb pinball System 1 manufactured 1980. I bought the pinball half a year ago without a working sound besides other issues.

The general optical condition of the pcb was quite good for my understanding. Due to my experience with other machine board of this age, I started to clean the board and replaced all electrolytic capacitors and potentiometer.

The circuit consist of a 6503 with a prom and a 6530. I read all over the web, that often times the 6530, which has an internal prom, looses the function. So I found a piggy back solution to replace the 6530 by a 6532 and an e2prom. Once done nothing happened. As I had a bit time pressure to make the game working for a bigger party I found the last 6503 on the market in our region. Again without success. Unfortunately I realised later, that the IC was installed in the wrong direction. No idea whether the 6503 IC survived the stupid action :-/ As I got angry in the meanwhile I put the pcb on side and board a repro with same form-fit-function. So far so good.



But to be honest I would make this original board working even if in the meanwhile lot of the electrical parts have been replaced. If somebody is interested in this, I have attached some pictures and the datasheet of the board.

When I read here thru the posts that I feel confirmed not to make the same approach again as I did... just replacement... better I have to go thru the scheme and try to varify what should be.

I will post my observation and ideas the next days/ weeks and if somebody has some helpfull comments in his mind....

Thank you so far!

Hello, and welcome to the forum!
Because your board has a power supply on it, I'd start your trouble shooting there. Do you know how to diode-check the 4 diodes next to the edge connector (CR1-CR4 on your schematic) using your multimeter? If not, just let us know which model multimeter you have.

If those are OK, I'd check your voltages next with the board plugged in. I personally like to do this with all of the socketed ICs removed, but you've already applied power with them installed so it may not matter. Using one of the bolts on the 7805 regulator (with the heatsink) as ground (black multimeter lead), you can measure the two pins that stick through the board with the red multimeter lead. One should be around +14V and the other should be around 5V. The last voltage you need you can measure across C9. That should measure 12V (it says -12V on the schematic, but that just depends on which way around you connect your multimeter... if you hook your black lead to the - stripe side lead of the capacitor, it will read as a positive value on your multimeter, and that's fine).

Then, touching the metal can of the regulator with the black lead of the multimeter (you may need to scratch it a bit with the probe to get a good connection), I'd probe the following places with your red multimeter lead:
Pin 5 of the 6503 is VCC and you should have close to 5V there.
Pin 2 of the 6503 id VSS and you should have close to 0V there.
Pin 1 of 6503 is /RESET (as generated by U5, the NE555P chip and inverted by U6, the 74HCT04N) and it should be HIGH (around 5V) very shortly after powerup and it should stay high.
Pin 28 of the 6503 is the phase-2 clock - if your multimeter has a frequency counter function, you could try that on this pin. You want this pin to be oscillating. You can also use the logic tester here, and it should show the oscillation (may indicate high and low at the same time, as this is a fast oscillation).

That's probably a good start. I see your add-on board replaces the impossible-to-get parts and it replaces both the program ROM and the separate sound data PROM. It should be fine to use that board as long as the EPROM has the program for your machine properly selected using the DIP switches on that board.

If all of the above are good, I'd check U3 (the MC1408L8 digital to analog converter) to see if it's getting digital signals and generating analog ones and then U8 (LM390N) is the amplifier that makes it strong enough to drive a speaker. I was initially concerned about the soldering on the amplifier IC, as many of the pins look shorted together; your schematic shows that all of those pins are indeed connected to GND, so it actually looks good for that.

(edited lightly for clarity when describing multimeter connections)