System 80 blues (Cont...) - Cassette Fixed!

Seek advice, give advice or tell others about your repair and restoration projects

System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Sat Sep 25, 2010 11:54 am

I've decided to contine the story I started in the General Forum here, now a forum dedicated to repair issues exists...

Well, the cassette player is now working 100%. The cause? Faulty labelling in the Dick Smith schematic in the Technical manual
(see http://www.classic-computers.org.nz/sys ... ematic.jpg)

In that schematic capacitor 7 is labelled in that schematic as 200uf. 200uf is also what I found IN the cassette player when I first opened it. Given that the schematic said so, and the previous capacitor in there was 200uf, I replaced it wth 200uf.

However, in the board layout in the link below this capacitor is labelled 10uf.
http://www.classic-computers.org.nz/sys ... corder.jpg
Also, in the troubleshooting guide, the manual also talks about replacing the 10uf C7 capactor with a 47uf one (not the 200uf one with a 47uf!).
http://www.classic-computers.org.nz/sys ... page54.jpg

After reading that I replaced C7 with a 47uf. Much better!...but not perfect. On occasions the signal was still dropped. I then replaced it with a 10uf one.

No sign of a problem since!

I noticed the C7 10uf on the layout diagram but dismissed it as maybe being an earlier revision. If I'd read the troubleshooting guide earlier I would have been suspicious enough to consider the schematic was mistaken rather than the board layout diagram. Obviously an earlier owner had been caught out by that one as well!

I also opened up my Blue Label model to see what kind of a C7 capacitor it had on the cassette deck. You guessed it. 10uf!
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby nama on Sat Sep 25, 2010 12:50 pm

Yeeeha! That's great news, and a great bit of detective work.

I was thinking about the freeze issue again, does it happen to coincide with moving the machine at all, or is it completely random?

Phil
Retro computing at: http://www.neoncluster.com
nama
 
Posts: 120
Joined: Mon Apr 19, 2010 12:13 am

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby ZL2AOX on Sat Sep 25, 2010 4:14 pm

That's odd. C7 looks like it's just a decoupler. As such, its value shouldn't be that critical and I wouldn't expect it to affect the gain. I suspect there may be a problem elsewhere, but if it appears to work ok... :D
ZL2AOX
 
Posts: 74
Joined: Sun Sep 12, 2010 12:30 pm
Location: Palmerston North

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Sat Sep 25, 2010 5:41 pm

Well Mark, you just may be right.

The cassette player seems to load ok now. I haven't had a failure since I changed that cap and I've loaded quite a few programs HOWEVER.....

A few weeks ago I restored another System 80's tape deck which had a similar problem. There a capacitor replacement of C7 and a few others seem to fixed the problem. BUT..I just opened up the machine and checked which cap I used as a replacement in that machine. It was 200uf. Yet it works?

So yes..the jury might still be out on this one.
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Freeze problems circumnavigated

Postby tezza on Sat Sep 25, 2010 5:51 pm

I did some more tests on the machine. The erratic behaviour does seem to increase when the computer warms up so it might be heat related. An old IC just not withstanding the heat like it used to maybe?

Anyway, I have solved the immediate problem but it's not really a fix. I found the only thing wrong with the CPU board on the SECOND System 80 in Kenneth's lot was a faulty CPU. I've replaced that and swapped that board for the one with the erratic behaviour. I then ran it with a burn-in RAM exerciser program for about 4 hours today. It worked just fine. Games seem to load and everything appears AOK.

I'll keep the erratic board as a source of spare parts and might look at it again in the future. In the meantime I
ll move onto the final stage...deyellowing the keys (and just hope the cassette player doesn't decide to go on strike again).
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby nama on Sat Sep 25, 2010 7:34 pm

That's great news. The issue with the original board could indeed be heat related, and these things are always difficult to track down. Seems that after all that effort you managed to resurect everything, turning two dead systems into one fully functional one. I wouldn't be surprised if you even got the other dead machine working at some point in the future.
Did you test the recording to tape?

Well done!
Retro computing at: http://www.neoncluster.com
nama
 
Posts: 120
Joined: Mon Apr 19, 2010 12:13 am

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Sun Sep 26, 2010 4:11 am

The recording doesn't work. Some missing componentry to do with the network modification I think. It should be easy to restore the second cassette port at some stage, although getting a relay might be a problem. Some kind of manual switch modification might be needed for this.

The unit's cleaned up quite nicely despite the carvings in the case. Once the key are white rather then nicotine yellow, it won't be too hard to look at.
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - 2nd machine fixed!

Postby tezza on Sun Sep 26, 2010 10:14 pm

nama wrote:I wouldn't be surprised if you even got the other dead machine working at some point in the future.

By good fortune I have! Suspecting an old RAM IC was failing when it got warm I removed the 32k mod, and filled the sockets with known good 4116 chips. I then turned my attention to the dead cassette player. I had to get this going before I could load software that would allow me to test my theoy that it was one of the ICs in the 32k RAM bank causing the problem. On inspection I quickly found the reason for the dead cassette. A broken power lead, This was repaired and whaddayaknow...wheels turned, flywheels whirred...the cassette was working. At least mechanically it was.

This cassette deck was an original Mk1 type with no meter or volume control. I used a process that nama suggested in an email i.e. to use one of those MP3 player cassettes. These are dummy cassettes which take an audio input. They are used in cars which have a cassette player, to enable MP3 players to be used with the car audio system. I hooked this up to my computers sound card and used my PC to send audio tape images directly into the System 80. Although I didn't have a meter, I did have a volume control on the PC. I manage to get the level right on the second attempt and the arrangment started to load in programs just fine.

I ran some tests, played some games for about an hour (including one that ALWAYS froze the board when the original RAM was present) with no issues at all. I'm confident it was a dodgy RAM chip and that the machine is now fine!. Some cleaning up, key-deyellowing, removing the school network components, adding the missing ones for the second cassette togther with a switch to swap between two and you're looking at a reasonable and usable 16k machine for this second unit!

I'm off to bed happy!
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby nama on Mon Sep 27, 2010 2:51 pm

Well, I'm certainly not that surprised. I think your dedication and love for these machines made it inevitable that it would get fixed someday. What does surprise me is how quickly you did it!

Anyway, huge congrats, there is nothing more satisfying than bringing the dead back to life.

Phil
Retro computing at: http://www.neoncluster.com
nama
 
Posts: 120
Joined: Mon Apr 19, 2010 12:13 am

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby nama on Mon Sep 27, 2010 2:52 pm

P.S. I'm excited to see some pictures of the final machines.
Retro computing at: http://www.neoncluster.com
nama
 
Posts: 120
Joined: Mon Apr 19, 2010 12:13 am

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Mon Sep 27, 2010 7:43 pm

nama wrote:P.S. I'm excited to see some pictures of the final machines.


I'll de-yellow the keys first. Then I'll take some pics of the final result. They will still be a little rough around the edges but they'll look a whole lot better than they did :)
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Wed Sep 29, 2010 9:04 am

Now that I've repaired both System 80s from the System 80 haul, I've started to document the repairs in my blog. For those that might be interested in reading the details (and seeing some pics) the url to the first installment is:
http://www.classic-computers.org.nz/blo ... am-fix.htm

There will be four articles for the first machine and one or two for the second.
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Fri Oct 01, 2010 11:41 am

For those interested, here is the second installement on the repair. This one focuses on the cassette issue. Some of this was covered in this thread but the blog article has pics!

http://www.classic-computers.org.nz/blo ... te-fix.htm
Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Sat Oct 02, 2010 8:55 pm

Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Re: System 80 blues (Cont...) - Cassette Fixed!

Postby tezza on Sun Oct 03, 2010 9:36 pm

Tez (Terry Stewart) (Administrator)
Collection: http://www.classic-computers.org.nz/col ... /index.htm
Projects and Articles: http://www.classic-computers.org.nz/blog/index.htm
Twitter: @classiccomputNZ | YouTube: Terry Stewart
Trade Me: tezza5
tezza
Site Admin
 
Posts: 2291
Joined: Thu Jan 01, 1970 12:00 pm
Location: Palmerston North, New Zealand

Next

Return to Repair and Restoration

Who is online

Users browsing this forum: No registered users and 2 guests