Sinclair ql black screen

[Traindriver69]

Hi
I have took all the seated chips out and gave them a quick clean a few days ago so today I was going to have another look at the sockets but as I tried to pull the cpu out I have broken the top of the socket so will need to replace that in the next couple of days before I can try anything else.

[Popopo]

Hi
I have took all the seated chips out and gave them a quick clean a few days ago so today I was going to have another look at the sockets but as I tried to pull the cpu out I have broken the top of the socket so will need to replace that in the next couple of days before I can try anything else.

I am sorry to read that
The CPU is one of the most complicated ICs to take out. Must be done very very carefully and with good tools.
How are you going to replace the socket?
if you have a hot air gun, that would be the best option, or another tool you could have around.

I guess you have soldering skills, if so, you also would place sockets on the RAM ICs. what will make much easier future replacement.
Also would be interesting to get some RAM ICs replacement. Usually 3 extra are enough.

Please, if you hesitate how to proceed, ASK. But I guess you have more than enough acknowledged.

[Traindriver69]

I do have a vacuum desolder and a hot air station I am not the best at soldering so fingers crossed it s there anything to watch out for when doing it,

[Traindriver69]

Bit the bullet and replaced the cpu socket

It's booting up as before so I think everything went OK.

[Popopo]

I will upate this message as soon as I get some time free. But I forward some advises and tips in order to avoid something bad.

Some soldering tips & considerations:

For Vacumm desolder

• Usually the old soldering joints are not easy to pump. vacuum desolder and a hot air station never mind, so adding some solder wire "renew" the joints and make it easier to extract later.
• Long ICs are the most difficult one to remove. You need to be very very patient and take your time, repeating the process as many times as necessary.
• vacuum desolder requires to use the right nozzle for the rivets of the PCB, use the right angle of application and do not to press in excess with high temperature, DO NOT move it around as so many youtubers said, that is a shit that may destroy tracks & rivets.
• For small ICs, the best (IMO) is hot gun air.
• In some cases, cutting the long IC into 2 pieces are not too bad if the socket doesn't get out easily (for any reason, skills, good tools, bad PCB, whatever). In that case, be very very careful to do no damage the PCB scratching it. Also some rivets or tracks could result damaged.

For Hot Air Gun

• Usually the old soldering joints are not easy to pump. vacuum desolder and a hot air station never mind, so adding some solder wire "renew" the joints and make it easier to extract later.
• Use kaptom belt to cover the adjacent area to the desolder zone, when using hot air gun.
• For small ICs, the best (IMO) is hot air gun.
• In some cases, cutting the long IC into 2 pieces are not too bad if the socket doesn't get out easily (for any reason, skills, good tools, bad PCB, whatever). In that case, be very very careful to do no damage the PCB scratching it. Also some rivets or tracks could result damaged. There are many ways, one of my favourites are using the iron solder enough hot to cut it as butter with hot knife, but do not abuse of it. Usually to divide it by 2. Avoid to get the hot iron to the board, do it laterally.
• Using hot air (practice a little with another board firstly), be careful with the temperature or long times of exposition. Practice firstly with another PCB. 380-390º with a medium flow, at distance of a hand, give not bad results. Do not let the hot air in a fix position, it need to be moving as you were preparing your best sauce in a great pane.
• Since it is not SMD board, I would use a regular nozzle.
• For RAM ICs that are not socked, you do a way that I will shot you later with some photos. Mainly is to use a weight to pull it down while you apply hot air over it.

Later I will continue, please to wait till you read all info and see some photos to follow. You have time, no need to be in a rush.

[Popopo]

Bit the bullet and replaced the cpu socket
It's booting up as before so I think everything went OK.

Very nice work!!!
Congratulations

Did you take photos before and after soldering the new socket?
That usually helps a lot to track possible unseen problems.

Now you could proceed with removing to socket the RAM ICs.
Do you dare?
(who dares wins!)

[Traindriver69]

Would it be worth getting some more ram chips first and try piggy back a few chips to maybe save some unsoldering and if that fails which chips would it be worth changing first to try and get the minerva memory check to work.

[Popopo]

Would it be worth getting some more ram chips first and try piggy back a few chips to maybe save some unsoldering and if that fails which chips would it be worth changing first to try and get the minerva memory check to work.

You are completely right.
It is better to wait.

It was me who was in a rush at the end

[tofro]

I'm actually not getting why you haven't replaced IC21 that you have (IMHO) identified as faulty in post 67. It is possible, but very unlikely, that the B side is completely grounded by defective RAM chips.

[Popopo]

Hi
Forget what I said about the VCC voltage as the pinout I was following although it said it was the right chip was wrong so now have rechecked and voltage is fine and DOut and address lines showing activity. IMG_20250710_123608_edit_44377249836977.jpg

I don't see clear 2 things here:

Firstly the pin#1 from the main ROM. It looks weird connection (what could produce what you suffered in the very begging with different ROMs).
The second is the transistor, this leads aren't clear for me.

Please, could you post better images from them? also check they are well connected. Mainly the ROM pin.