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Bootleg Pac/MsPac help


zwooky

Question

Recently unpacked my bootleg PCB from storage that used to be in working order but now it doesn't. I've attached some screenshots of what the screen looks like when I boot up and of the PCB itself.

It appears to be a variation of the PAC3 bootleg (http://lawnmowerman.rotheblog.com/#bootlegs) on a Falcon II (KPM-II) board.

Not sure if it's a ROM, adapter, or trace issue.

Any ideas where to start, Z80, video RAMS? Anyone know of any schematics for a board such as this, or where I can send it to get it looked at?

Thanks!

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Screen.jpg

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I have a logic probe (no scope). I've never tested a Z80 before, could you give me a quick primer?

I'd definitely just replace it but it'll take long to get a new one. In the meantime I'd like to test this one if I can.

 

Firstly grab yourself a copy of the Pacman-MsPacman-Troubleshooting-Guide-Part1.pdf

The schematics are useful even though you have the bootleg. There are some differences like the sync buss controller used on the original but much of the IC's etc remain the same.

 

Check pin 26 on the Z80 which is your reset line which should be high and check pin 6 which is the clock which should be pulsing.

Common issue on these boards are the 2114 and the ones on your board are notoriously prone to failure going 35+ years on ( I just did a bunch of this vintage boards).

Unfortunately yours are not in sockets.

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Thanks tips and the link to the Troubleshooting guide, hadn't seen that in my searches.

Check pin 26 on the Z80 which is your reset line which should be high and check pin 6 which is the clock which should be pulsing.

Got a high on pin26, & a pulse on pin6. The guide says pin26 should go low with a reset, how do I trigger a reset to test this?

Common issue on these boards are the 2114 and the ones on your board are notoriously prone to failure going 35+ years on ( I just did a bunch of this vintage boards).

Unfortunately yours are not in sockets.

I've got 6 of these on the board, just like the guide shows (guide also describes the problem of all 0's showing as a failure of one of these) how do I test these? Do I need to pull them out & put them in a chip tester, or can I do it with my logic probe? Looking at the datasheet for the chip ,but it doesn't make sense to me yet. Can anyone decipher it for me?

 

https://console5.com/techwiki/images/7/7c/TMM314APL.pdf

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If the reset line is sitting high and not toggling high/low (watchdog barking) then its safe to say its ok.

With the rams you can piggy back known good ones on top in a pinch, you really need to have spares of these.

 

IMG_20190913_062932.jpg

I had one of those Falcon bootlegs years ago and was recently given it back.

Look familiar? :lol

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So the chips finally arrived and I've piggybacked them onto the current ones & now I get this:

 

https://imgur.com/a/olUZYqG

 

The red is probably just me needing to adjust the RGB-HDMI adapter.

 

Any thoughts?

 

That's good, it means its trying to boot up.

I'd socket all those rams.

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When I was piggybacking the chips, only 4L made any change from the all 0's screen. Took way too long to de-solder and put that chip and 4K in, now here's what i got.

 

https://imgur.com/a/ZYZvA3v

 

Color changed and there's letters and #'s flashing instead of unintelligible symbols. You can start to make out RAM 0 of the self test for a split second.

Think I'm on the right track, hopefully. Next 4 chips are gonna take me forever!!

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When I was piggybacking the chips, only 4L made any change from the all 0's screen. Took way too long to de-solder and put that chip and K4 in, now here's what i got.

 

https://imgur.com/a/ZYZvA3v

 

Color changed and there's letter and #'s flashing instead of unintelligible symbols. You can start to make out RAM 0 out a little bit.

Think I'm on the right track, hopefully. Next 4 chips are gonna take me forever!!

 

Good work.

Looking at the manual Ram 0 is either 4k or 4n. If the order of the rams are the same on the Falcon 4h or 4j could be faulty.

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Did you use sockets? If so you can remove the ram chips and check that each pin is connected to a track on the board. Otherwise if you have a probe check the data & address lines of each chip to make sure they're pulsing.
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This is definitely getting frustrating now.

  1. Pulled out the chips and put in sockets
  2. Checked for continuity across the sockets (good where it's supposed to be based on the traces)
  3. Still getting a white screen with scrolling flashing cherries
  4. Used probe to check address (pins 1-7,15-17) & data lines (pins 11-14) and got a pulse on all except 1-3 address. https://console5.com/techwiki/images/7/7c/TMM314APL.pdf

Does this mean the chips are damaged?

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You mean no pulse on pins 1,2 & 3 ?? They are address lines A4,A5 & A6 so they should definitely have signals on them.

 

1. Check that you haven't damaged any through hole connections.

2. Remove the ram chips from the sockets and check the address lines again, they should be pulsing even without the RAM chips installed.

3. If still no pulsing, you'll need to trace back to find where the address lines stop working. Also check them at the CPU and work outwards.

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I haven't had much time to work on this board but it appears I have damaged 2 of the eyelets on the pcb of 1 of the RAM chips. At some point I'll work on that & report back.

I also have one of those IC chip testers on the way, just to make sure I haven't shorted or damaged any of the chips.

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