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Re: General Stuff(tm)
Posted: 03 Jan 2024 20:41
by PhilC
Is it possible it can be memory related? I’ve fixed a few QLs that either had bad memory or 74LS257 chips.
Re: General Stuff(tm)
Posted: 03 Jan 2024 20:49
by stephen_usher
PhilC wrote: 03 Jan 2024 20:41
Is it possible it can be memory related? I’ve fixed a few QLs that either had bad memory or 74LS257 chips.
It passes the memory test but fails the POST it seems, getting to stage 5.
Re: General Stuff(tm)
Posted: 03 Jan 2024 21:15
by stephen_usher
Found the diag list!
OPD-Errors.JPG
So, looks like an SRAM issue. I'm guessing that it's actually caused by the back-up battery being bad.
Re: General Stuff(tm)
Posted: 03 Jan 2024 21:57
by rubber_jonnie
Oooh, interesting, be good to see what fixes it.
Re: General Stuff(tm)
Posted: 04 Jan 2024 19:20
by stephen_usher
I was going to go out and do some more work on the OPD tonight but I'm not going out in this rain. I'd get soaked just getting to my outbuilding and opening the door.
Re: General Stuff(tm)
Posted: 06 Jan 2024 13:12
by stephen_usher
Well, found the problem causing the "SRAM" error.
I took the machine apart and found that /CE1 on the SRAM chip was not going low. Traced this over to an inverting transistor on the far left of the board... and then traced the control of this transistor over to the mid-right and then rear of the board... And onto the monitor/power input socket.
It turns out that this is the power-good signal from the power supply.
So the problems were caused by a bad connection on the connector to the PSU board, but only the power-good line. *sigh*
Of course, by opening the machine up I've caused another problem, this time the keyboard.
Re: General Stuff(tm)
Posted: 06 Jan 2024 14:13
by rubber_jonnie
stephen_usher wrote: 06 Jan 2024 13:12
Well, found the problem causing the "SRAM" error.
I took the machine apart and found that /CE1 on the SRAM chip was not going low. Traced this over to an inverting transistor on the far left of the board... and then traced the control of this transistor over to the mid-right and then rear of the board... And onto the monitor/power input socket.
It turns out that this is the power-good signal from the power supply.
So the problems were caused by a bad connection on the connector to the PSU board, but only the power-good line. *sigh*
Of course, by opening the machine up I've caused another problem, this time the keyboard.
What's up with the keyboard?
Re: General Stuff(tm)
Posted: 06 Jan 2024 14:35
by stephen_usher
Some of the keyas wouldn't work. I've reseated the ribbon cable and it's fine now. *phew*
Re: General Stuff(tm)
Posted: 06 Jan 2024 16:25
by rubber_jonnie
stephen_usher wrote: 06 Jan 2024 14:35
Some of the keyas wouldn't work. I've reseated the ribbon cable and it's fine now. *phew*
Phew indeed!
Mine had a couple of bad rubber domes, but luckily I had some spare domes from an ST, and though it was a faff, they do work.
Re: General Stuff(tm)
Posted: 06 Jan 2024 17:15
by stephen_usher
One shift key has an issue with its dome. Good to know that ST ones work, not that I have any spare.
P.S. Just bought one from eBay.