Got a 'new' 6128 - fully working!

[Munchausen]

As you might be aware I've had a lot of trials and tribulations getting my CPCs to work with various bits of hardware. Well I got another 6128 last week, and spent most of today playing on it - and everything works perfectly! So I just thought I'd share my joy with you - woohoo!


One day I hope I'll repair the other two 6128s. One of them at least works fine as long as you don't want to use the expansion port. At least I have a bunch of spares as well.

[Bryce]

Congratulations.

What exactly happens when you connect something to the expansion port? Does it not turn on? Crash? Or does the expansion just not work? Weird failure either way, but probably something very simple.

Send over the PCB if you like and I'll check it out.

Bryce.

[Munchausen]

It acts strangely! IIRC, it gets strange screen artifacts or sometimes wont turn on. With the symbiface plugged in and the symbos ROMs present, it often powers up ok (with the symbos ROM boot message) but then if you try to launch symbos it gets stuck halfway to booting or you get odd screen corruption. I had a lot of issues with the lowerrom on that machine too, it would sometimes boot but be slightly garbled or freeze just after boot. Also get weird colour patterns on startup sometimes. Without anything in the expansion port it works fine - and the floppy connector also works great.


I used a multimeter to buzz out all the pins from the end of an expansion cable to the connector, then from the connector pins to the places they route to on the motherboard, and they all came out fine. So I think there is some sort of intermittent fault or something else weird with one of the lines. I think you advised that I could do some sort of test with an oscilloscope, but I didn't fully follow and my scope is really bad anyway and I've never really got it to work properly (it's this one: [size=78%]http://www.conrad-electronic.co.uk/ce/en/product/120980/---Velleman---HPS-10---1-Channel-hand-held-oscilloscope-Scope-Meter-hand-held[/size]). I need to get a decent analog/CRT scope but can't really justify the cost ATM.


If you could take a look at it for me that would be awesome! I'd really like to have a backup machine.


The other 6128 is one I put 12V into. I replaced the RAM and CRTC and got it sort of working, but it is unreliable at best and does really odd things.

[TheCorfiot]

I would try changing the Z80 on the one with expansion port issues.


TC 

[Bryce]

It acts strangely! IIRC, it gets strange screen artifacts or sometimes wont turn on. With the symbiface plugged in and the symbos ROMs present, it often powers up ok (with the symbos ROM boot message) but then if you try to launch symbos it gets stuck halfway to booting or you get odd screen corruption. I had a lot of issues with the lowerrom on that machine too, it would sometimes boot but be slightly garbled or freeze just after boot. Also get weird colour patterns on startup sometimes. Without anything in the expansion port it works fine - and the floppy connector also works great.


I used a multimeter to buzz out all the pins from the end of an expansion cable to the connector, then from the connector pins to the places they route to on the motherboard, and they all came out fine. So I think there is some sort of intermittent fault or something else weird with one of the lines. I think you advised that I could do some sort of test with an oscilloscope, but I didn't fully follow and my scope is really bad anyway and I've never really got it to work properly (it's this one: [size=78%]http://www.conrad-electronic.co.uk/ce/en/product/120980/---Velleman---HPS-10---1-Channel-hand-held-oscilloscope-Scope-Meter-hand-held[/size]). I need to get a decent analog/CRT scope but can't really justify the cost ATM.


If you could take a look at it for me that would be awesome! I'd really like to have a backup machine.


The other 6128 is one I put 12V into. I replaced the RAM and CRTC and got it sort of working, but it is unreliable at best and does really odd things.

The first thing I'd do is properly clean the contacts on the expansion port. Even just a tiny layer of oxidation will cause this kind of thing.

Bryce.

[TotO]

Yes, it look like a dirty/oxidized expansion port.
About the CPU, never replace it with a CMOS version, as it will cause random bugs too.

[Munchausen]

Well IDK, I did clean the contacts already (with white spirit I think, might have been something else similar I can't remember - whatever it was it's what my GF uses it to clean her paint brushes).


Then after that didn't work I soldered IDC pin headers on, and that didn't work either.


I'll try swapping the Z80 out with one from my 464. If that doesn't work then I think I am going to send the PCB to you Bryce, if that's ok?

[Bryce]

Yeah sure, send it over. Sounds like an interesting one to look at.

Bryce.

[Munchausen]

Going to the post office tomorrow, will let you know when it's on its way

[ralferoo]

Well IDK, I did clean the contacts already (with white spirit I think, might have been something else similar I can't remember - whatever it was it's what my GF uses it to clean her paint brushes).

Just FYI, the acetone in nail varnish remover will tend to eat through the solder resist layer too. You really want isopropylalcohol (IPA) for cleaning PCBs.

[Gryzor]

Plain alcohol with no additives should be more than fine


As a note, the other day I was setting up a MegaDrive for the retro cafe nearby; although the machine's AND cartridge contacts looked in perfect condition, it proved they did need cleaning... so never be sure!