Derek_Stewart wrote: Tue Oct 15, 2024 10:36 pm
thecaver99 wrote: Mon Oct 14, 2024 10:25 pm
It turned out to be 5 dead ram chips, 1 in lower ram and 4 in upper ram.
All replaced and now the ql lives once more.
Hi,
I am updating the QL Service Manual, and introducing a fault finding section.
Since you have just successfully repaired a QL, could detail the process that that you went through to repair your QL.
This would maybe help other QL owners in the future.
yeh no problem, i will give you what i have.
i had a bit of the green/red/white pixels then white screen, from reading this pointed to upper ram issue.
tested as the service manual asks to use a ground lead and short out pin 2 on the 4164 and each chip showed a black line on the scree.
fitted an ice over the top of each of the upper ram ics no change, porobed all the address lines with m y scope and nothing was changing, activity one the data pins, ras, cas, w etc.
this lead me to belive that i had more than 1 ic bad.
removed all 8 upper 4164 ics, fitted dual wipe sockets and fitted 8 tested new 4164 and got a black screen, so some progress,
left system on for a couple of mins and found 1 lower ram chip was getting extreamly hot, removed and fitted socket and new 4164 chip.
powewred on and fgot the normal screen F1/F2.
tested each of the upper ram chips by replcing one of the new ones and found 3 dead, replced the woking ones for the new ones,
if the minerva rom had arrived before hand that might have saved me a lot of hunting.
for video i am using the RGB port hooked upto an rgbtohdmi adapter and have lovely crisp video output.
now awaiting a replacement membrain and bubble mat and new minerva rom for the QL.
also waiting on a mirical systems 512k ram card and a floppy controller so i can finly get some software on to the lovely looking QL.
