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General Category => Technical Support => Topic started by: backtogeek on 13:07, 11 December 20

Title: Odd display problem - anyone seen this before? (cpc 464)
Post by: backtogeek on 13:07, 11 December 20
I had a quick search on the forum, could not find anything specifically like this, i wondered if anyone has seen this before or has any suggestions on what it may be caused by?


https://i.imgur.com/fR6xcsI.jpg (https://i.imgur.com/fR6xcsI.jpg)
https://i.imgur.com/30Hwdi4.jpg (https://i.imgur.com/30Hwdi4.jpg)
https://i.imgur.com/MIkumg8.jpg (https://i.imgur.com/MIkumg8.jpg)
https://i.imgur.com/lRyMqiT.jpg (https://i.imgur.com/lRyMqiT.jpg)


It does not seem to impact the function at all, I left it running like that for an hour or so, no change.

edit: sorry the images did not resize so just posted links to the images instead.
Title: Re: Odd display problem - anyone seen this before?
Post by: backtogeek on 13:07, 11 December 20
Sorry about the images I expected them to auto resize
Title: Re: Odd display problem - anyone seen this before?
Post by: Bryce on 14:25, 11 December 20
Yes, I had a CPC in for repair that did that. From what I can remember (it's a long time ago) it was a dodgy RAM that was on the verge of failing. However, the CPC in question had other issues, so I can't say for sure that that was the real cause. Leave it running for as long as you can, that might cause the RAM to fail completely.

You could also, try re-seating the CPU or try a different CPU to see if it goes away.


Bryce.
 
Title: Re: Odd display problem - anyone seen this before?
Post by: backtogeek on 15:02, 11 December 20
I have a z80 from that short board you gave me some advice on that I could not fix yet, so I will try swapping the z80's over, thanks Bryce.


Will they boot without a full ram compliment? I could always try taking out a bank at a time.
Title: Re: Odd display problem - anyone seen this before?
Post by: Bryce on 15:18, 11 December 20
If it's a 6128 it will boot with just the lower 64K in place, but it won't boot if any RAM is missing from the lower 64K.

If you don't have any luck with either of the boards, you can send them over to me for repair.

Bryce.
Title: Re: Odd display problem - anyone seen this before? (CPC 464)
Post by: backtogeek on 16:26, 11 December 20
If it's a 6128 it will boot with just the lower 64K in place, but it won't boot if any RAM is missing from the lower 64K.

If you don't have any luck with either of the boards, you can send them over to me for repair.

Bryce.


Thanks, its a 464 (added to the forum subject for clarity), I am going in now, wish me luck!
Title: Re: Odd display problem - anyone seen this before?
Post by: backtogeek on 16:39, 11 December 20
You could also, try re-seating the CPU or try a different CPU to see if it goes away.

CPU swapped same issue, I will try switching some of the ram, I assume the short board ram is compatible... desolder time, always fun.
Title: Re: Odd display problem - anyone seen this before?
Post by: Bryce on 16:44, 11 December 20
They should all be 4164 RAMs.

Bryce.
Title: Re: Odd display problem - anyone seen this before?
Post by: backtogeek on 17:20, 11 December 20
sadly my solder pump is no match for the volume of solder that is half way up the legs on the other side of the board too and I dont want to wick it and risk damaging the ram.

the one with this fault has socketed ram anyway so I will just buy a few 4164's and be patient.
Title: Re: Odd display problem - anyone seen this before?
Post by: Bryce on 17:30, 11 December 20
If the RAM is socketed, I'd definitely try re-seating all the RAM ICs first.

Bryce.
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: backtogeek on 17:38, 11 December 20
yep I did that, no difference, then I swapped them all over so each one was in a different slot to see if that changed anything, it did not, ordered a 4146 should be here in <7 days so will start testing with the replacement in each position.


Can you piggy back them for testing like you can with the amiga? I imagine its fine.
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: Bryce on 17:40, 11 December 20
Piggybacking only works in some limited circumstances, whether it's a CPC or Amiga doesn't matter. RAMs can fail in many ways and piggybacking won't work for many failures.

Bryce.
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: GUNHED on 23:07, 12 December 20
That's grid bugs! Try to use a different PSU, if you have one at hand.
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: backtogeek on 22:33, 14 December 20
That's grid bugs! Try to use a different PSU, if you have one at hand.


Would it cause that on any CPC464, asking as I have gone through 4 in the past few months all on the same PSU and none of them have that, maybe this one is just particularly sensitive?
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: GUNHED on 23:06, 14 December 20
Then no PSU... Open the CPC. let it run for 1 hour. Tap at the RAM chips (and others if you like). Fell of one IC gets particular hot. This may be the broken one.
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: backtogeek on 10:24, 16 December 20
Then no PSU... Open the CPC. let it run for 1 hour. Tap at the RAM chips (and others if you like). Fell of one IC gets particular hot. This may be the broken one.


I have 3 commodore 1530 datasettes to recap and service today and once I have made space again (I am a messy worker) I will power it back up for an hour or 2 and see what gets hot. thanks.
Title: Re: Odd display problem - anyone seen this before? (cpc 464)
Post by: lazapap on 00:32, 31 December 20
I had some similar problem with a cheap 5V power supply. Try to take power from a pc's or laptop's usb port, it's safer.