Atari 520ST help (glue chips?)

[Spirantho]

22pF is too small for an electrolytic, and other types don't usually go bad.... I'm thinking trying replacing the 1N914, what do you think?

[Nyh]

22pF is too small for an electrolytic, and other types don't usually go bad.... I'm thinking trying replacing the 1N914, what do you think?

A broken 1N914 will pull the signal up to 5 V and will leak the VSYNC signals on the HSYNC line. I don't expect this to be the problem, unless the 1N914 is broken and the composite sync circuit is broken too making the anode of the rectifier 0V all the time. There is no harm in looking at what happens over there.

Hans Wessels

[Spirantho]

I just noticed something! Resistance from pin 38 (VSYNC) to ground is just 10 ohms!
Now what's causing that....

[Nyh]

I just noticed something! Resistance from pin 38 (VSYNC) to ground is just 10 ohms!
Now what's causing that....

Find that and I think you have solved the problem!

Hans Wessels

[Spirantho]

It's in the modulator, but I can't get the darn thing off. I'm melting the solder on the modulator clips but it refuses shift!

Edit: Got it! Resistance is now 800Ohm. Now then.... let's see...

Edit2:
You rock! Thank you very much for all your help!

[spiny]

top work !

[wongck]

Well done !! [smilie=greencolorz4_pdt_12.gif]
Great to see another Atari device come back to life.

[Spirantho]

Thanks people - though most of the credit goes to the people on the forum (especially Hans).

Eventually I want my business to do Atari ST repairs like I do Spectrum repairs already. I believe http://www.st-freakz.co.uk/ may do repairs but I'm not sure. Either way never a bad thing to have more than one company doing repairs.

First I need to get more STs to get my skills up though. This experience has been great for my understanding of the ST though, I was lucky I got such a tricky machine to repair.

[Shredder11]

If you can do Falcon 030 and TT 030 machines, people will beat a path to your door!

[Spirantho]

Well, I guess I am prepared for it..

Falcon.jpg

The problem with the later STs is the amount of surface mounted chips, and impossible-to-get-hold-of custom chips. However, I could still do something as long as the ICs are ok. I need to get one of those Aoyue desoldering stations!

My plan is certainly to repair anything I possibly can though. My tally so far: about 50 Spectrums (seriously), one Acorn Archimedes A3010 and one Atari STm. Oh, and an Atari 1050 disk drive. And some ZX81s. And a few C64s. And a VIC-20. And a EACA Colour Genie.

Am I strange for getting a kick out of taking in an unloved, dead machine and bringing it back to life?

[ralcool]

Well, I guess I am prepared for it..

Am I strange for getting a kick out of taking in an unloved, dead machine and bringing it back to life?

Is this forum here for any other reason?... Most guys here are 30-50+ yr/old.... And probably remember Douglas Adams when he was still alive.

There is no shame in the kind of respect and understanding of the crazy logic that makes an old computer work. Some of us find comfort in the 'simplicity'

As you have discovered- its not actually entirely simple, but it is achieveable and rewarding.

Good luck mate & Well done.



ST.

[Spirantho]

A little update for anyone interested.....

When I put it back together without the modulator in, I noticed that (not surprisingly) it became an Atari 520ST - i.e. it didn't have +5V on the monitor port, so my TV couldn't understand the signal (no switching signal).

I took it upon myself to fix the modulator, which I have now done, so the Atari is now a fully working 2.5MB Atari 520STm.

And the culprit was..... <cue drum roll>....

The 74LS86!
I replaced that chip in the modulator and all is well.

Maybe someday this thread will help someone else.