Faulty CX5M

By grobda

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18-05-2022, 15:42

Hellos
I have a faulty CX5M that displays a garbled boot screen and cursor but with a lot of graphics corruption. It's tough to see but seems keypresses work, then the machine resets after a couple of seconds. There might be an error message, looks like 'system error' possibly but with the graphics corruption it's hard to make out. I suspected graphics ram was at least part of the fault initially so I pulled it all but its tested ok and makes no difference. So I pulled the system ram too and that also tested ok. The 245 buffers and 157 multiplexers between the CPU and RAM also tested ok. Any ideas? I'm suspecting the YM5214 next Eek!

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By Grauw

Ascended (10577)

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18-05-2022, 20:08

Hi grobda,

Can you post a picture of the graphics corruption?

By Alexey

Guardian (3375)

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18-05-2022, 21:04

What tester did you use for 4116 DRAM testing? The problem you described indicates VRAM corruption.

By grobda

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18-05-2022, 21:41

im afraid the machine is in bits at the moment as i bought another one with a damaged power connector (which arrived today) and used the dead one for parts, so no pics of the fault. basically there are 'wrong' pixels in every character block, IE ones that are blue should be white and vice versa, some flicker between, and it tends to get worse over time.

i used this for ram testing; https://www.ebay.co.uk/itm/124726020732. its flagged bad chips correctly before. I guess they could be borderline or it could be testing at a slower speed than the msx needs.

as i've now got a good machine i guess its a lower priority but i hope to get it running so I can enjoy some massive ym2151 polyphony B-)

By Grauw

Ascended (10577)

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18-05-2022, 21:48

You could put in new RAM chips and see if it makes a difference. I’ve seen RAM testers give false positives.

By grobda

Supporter (8)

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19-05-2022, 20:24

it's working again. replaced some borderline ram. the other problem was one of the 4050 buffer/drivers on the keyboard daughtercard was faulty causing it to constantly register 'shift+f5' ie the run command. so now i have two Big smile