Sinclair ZX80 / ZX81 / Z88 Forums

TR5 was perfectly fine, it did not need changing....

Mark

You absolutely spot on.
Should i put the original back?

Don't know what to do, never had issues like this where replacing a "simple" components would end up in strange results.
Gonna re-review all solder, all pcb connections for shorts or drops of solder or whatever....
what i can not really understand is why the 1st boot was normal and booted from dandanator card, ran the tests and after that never again.

So this morning spent +3h checking all i can in detail, retouching the solder on mostly everything i touched before or may have.
Now it's kind of back to the normal not working as expected after recap i guess.

So i have left the wire to disable upper ram (pin 5 of IC23 and + of C34), put lower ram board, boot it and goes to sinclair nice home screen, after a few seconds starts either beeping and goes to the white border black center or white border/black center and then some red stripes, sometimes sinclair home screen and then types K and other chars in screen and goes typing some lines and chars.

It seems is related to the time is powered off the random stuff i get after when power on, if left for longer time boots into sinclair text and beeps and then white border/black center, if i boot it few seconds after latest then does random stuff.

If i boot with dandanator card inserted and do no push for load test shows the normal screen menu of dandanator rom but blue text lines have like an underline line but on top of text.
If i boot the dandanator into load test program it loads and after doing those wizard stuff goes to RAM FAIL 01234567 white text and black with red thick lines.

All these with keyboard unplugged if that matters i do not know.


Also i do not remember if i mentioned there was always been as wire connecting 3 pins i think was a old repair someone did but has always been there and it was working fine like this before the recap.

It connects pin8 from eprom to 32 of cpu and to some other point under the cpu (image below). i was not sure if i somehow touched the insulation of this and re-soldered it when recapped it. No idea if matters but the pin32 of cpu where it is soldered feels like loose, i mean i touch it with probe and it moves.

So now i will not touch anything else and cross fingers you have opportunity to help me progress

Sorry, been busy with my real world job. I'll reply later once I've caught up.

Mark

1024MAK wrote: ↑Thu Jan 25, 2024 6:22 pm Sorry, been busy with my real world job. I'll reply later once I've caught up.

Mark

Always first!
I am already very thankful someone - you - is helping me!

Have a great time

Ok got my new ULA today but will not touch anything until Mark has a chance to give me a help to check what is needed and if i can plug it in.

Hi there Sinclair people!

So not all posts can be just about problems and ignorance in display
I am happy to report hat so far i have been able to play with my zx without issues (apart my all time favorite R-Type included in dandanator rom making strange artifacts)! All tests run fine and OK, been playing for 40m so far and seems all is working as expected.
So... what a long journey it was, having no idea on 99% of what i was doing and how these magic circuits work, went from joy to rage to self incrimination and then to it's alive again!

As mentioned before i had been delivered the last component i had ordered that was the ULA82.
I know... i know... i said i would not put it until Mark would come back to me....
But well... this morning spent like 2h under microscope checking all solders and traces, tested a lot to make sure they were working and not shorting somewhere, did a long clean with toothbrush and 98% alcohol on both sides of the board and just put the new ULA in.

And voilá! So far so good, can't see any issues with it and i am again (so far) happy that my very first computer is working!

So what i have done to it? Prob a result of a crappy soldering experience when i replaced the caps. The power regulator was ok but after caps... something very wrong was done. So at least 3 low ram chips were damaged along with TR4.

What does it have new:
- TRACO TSR-1-2450
- New TR4 and TR5 transistors
- New CAPS all around
- Phil Lower RAM Board
- ULA82
- New EAR connector
- Dandanator Mini 2.1
- Composite mod with cap

NOW most important and above all, i have to shout and give a BIG thanks to Mark!!!!!!!
Without you, even if i spent hours and hours reading online stuff about repairs and tried to make sense of the schematics and what else more, i could not have done it!
So from all my heart THANK YOU!

PS - now just to think how to solve the issue about he new ULA is too high to properly close the case

Plus cases come up quite often on ebay, pots more room inside if you don’t particularly want the original style. Otherwise you might need to pick up an original ULA.

redgatemodels wrote: ↑Sun Feb 04, 2024 5:09 pm Plus cases come up quite often on ebay, pots more room inside if you don’t particularly want the original style. Otherwise you might need to pick up an original ULA.

Thanks for the reply!
That is a good idea, and also i am considering if i will attempt to do a 3d model of the case then i could print and keep as stock like as possible.
Is something i have not much experience on but maybe will go for a try

You will only need a deeper case top building, all those curves though!