QL Not Starting Up

[RWAP]

Damn - one of the QLs I sold as part of my stock clearance has arrived but won't start up - see image below - is this a memory failure?

[tofro]

Rich,

I'm tempted to say that's an allergic reaction to a white monitor and keyboard No wonder it doesn't work.

Doesn't necessarily look like a RAM fault, could also be 8301. It would be interesting to know whether the QL went through the RAM test properly (i.e. the "random pattern" screen) before that screen or not.

Tobias

[RWAP]

No - that is the first thing he sees - he has swapped the 8301 already (that was my first thought!)

[tofro]

Apparently, the QL is trying to show a white screen (which means "first part of RAM test failure") and doesn't quite succeed. The repeating black dot pattern also means there seems to be a RAM fault in exactly one bit. Section 2.2.12. in the service manual describes exactly this case, I think, and also how to find the faulty chip.

Tobias

[Derek_Stewart]

Hi,

If you had Minerva in rom, it would of given code
. The code can identify the ram chip which is faulty, via the programme:ramfail_bas on the Minverva support disk or download from Dilwyn's web site. Pre-Minerva the ram has to individually tested.

[bverstee]

Hey guys, this my first post here.
I bought the QL from Rich (had some QL's in the past, but never did something with them) to test some add-on cards I had recently obtained, and because I may produce QL hardware in the future.

But unfortunately it had a small defect.
I think it was caused by a bad 7805, which didn't had a proper 5V output (about 4.7V).
After replacing it, the picture was a lot more stable, but white with some dots

Rich sent me a Minerva ROM to check the RAM error.
Thanks Rich!!!

I managed to solve the problem quite easily (I do dozens of ZX Spectrums per year, and it looks like the problem solving algoritm is quite the same).

Here's what Minerva told me:







This might look as a DB5 defect, so I replaced IC14 (took me some time to figure out the chip, as the architecture is a bit different).
It seems 4864 and 4164 are exchangeable, but I had some 4864's laying around, so I used that one.



Unfortunately this did not solve the problem, and the RAM errors seem to be inconsistent.
I read about a defective 74LS245 that drives the datalines in a QL on some website, so I replaced that one.



Problem solved!




Finally I could test some cards.
First the memory expansion:



Then one of the Trump cards:

[RWAP]

Excellent - glad you could resolve the issue - it looks as though the 74LS245 could be a good thing to check especially if the memory issue is inconsistent.

I wonder if it could be something similar on my Trump Card here (see another thread) where the QL just locks up or files get corrupt during transfer at various times - yet Minerva does not report anything (and the issue still happens on other QLs)

[1024MAK]

Welcome to the world of the QL, Ben

Good news on you locating and fixing the fault on your QL.

Do feel free to keep us informed of any QL products you are developing

Mark

[vanpeebles]

Welcome! New QL bits sounds exciting