Update 14/9/10: Cleaned the case today.  It's certainly an improvement!  I'm giving you the one which has the meter in it.  Given that you can't use cassette #2, I think this is quite important.  This has also determined what keyboard you'll get as the case with the meter ALSO has an extra ESC key (actually Reset) hole for the keyboard with the extra key.

These keys are quite yellow.  If I get time I'll de-yellow them for you.

One the weekend I'll see if I can fix the RAM and get the cassette going.

Update 19/9/10: Machine is now back to 32K.  Faulty RAM chip.  Some repacking/re-soldering required and RAM is piggybacked.

Cassette goes but is very dodgy.  Sometimes loads tapes and sometimes doesn't.  Needle swings around like a barn door.  Will replace some capacitors and hope for an improvement.

There is another issue though.  RAM test checks out ok but machine seems to seize up during games sometimes when keys are pressed.  Right arrow works in BASIC (gives a tab) but does not work in some games????  The The machine has a joystick modification and I suspect it might be this causing the problem. There seems to be a short over some of the pins.  Anyway. I'll remove it and see if that improves matters.

Update 20/9/10: I removed (de-soldered) the joystick mod.  It seems to have fixed the freeze-up problem when you press a key on games.  So that's good news.

What is not good news is the tape recorder.  I replaced nearly all the capacitors on the cassette board (except for one unimportant one dealing with the level meter).  The meter is a lot more steady now BUT there are two issues still.

1. Sometimes there is simply no signal 50% of the time.  Nothing.  It's very similar to the symptom on that unit I restored.  (Replacing caps on the restored unit seem to fix that, but I'm now beginning to wonder if it is actually DID fix it...or whether the problem is there waiting.!   That's the problem with intermittent issues)

2. The cassette recorder does not record at all.

I'm going to try replacing the IC on the cassette board.  If that doesn't work I'm going to swap the cassette board with the board on the second cassette.  There is a bit of soldering involved.  If that doesn't work I'm going to have to leave it at that.

The record issue could even be associated with the school modification. Could record have been disabled?  There are quite a few components missing on the video board to do with cassette functions and instead used by the networking modification.

Update 22/9/10: It's not looking good.  The freeze up problem has re-appeared so it hasn't been fixed after all.  Actually it's more than just a freeze up.  It's instability generally and doesn't always happen on a key press but often does.  It manifests itself as a drop into to BASIC, lines in the wrong places or even a return to READY?  It is intermittent, but run a program for long enough and it will show up.

It doesn't seem to be RAM.  When the unit is going it passes a RAM test ok. I'm wondering if it's caused by an intermittent drop in voltage, exacerbated when a key is pressed?  Power issues maybe?  There is no instability on the screen at all though?

I can't get to the bottom of the cassette problem.  I've now replaced EVERY electrolytic capacitor on the board, I've replaced the amp IC and also re-soldered every joint on the base.  No change. The cassette deck loads when it wants to and at other times there is no signal at all.  The heads are certainly working as I can see a small signal with a scope.  Voltages seem normal going into the cassette player.

I was going to swap over the board with that other tape recorder but the board is actually different.  It's an earlier deck with no meter so I couldn't do it.

Update 25/9/10: Well, the cassette player is now working 100%. The cause? Faulty labeling in the Dick Smith schematic in the Technical manual. 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 with 200uf.

However, in the board layout this capacitor is labelled 10uf. Also, in the troubleshooting guide, the manual also talks about replacing the 10uf C7 capacitor with a 47uf one (not the 200uf one with a 47uf!). 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!

Update 29/9/10: I did some more tests on the machine. The erratic behavior 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 the auction lot was a faulty CPU. I've replaced that and swapped that board for the one with the erratic behavior. 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...de-yellowing the keys (and just hope the cassette player doesn't decide to go on strike again).

neoncluster.com

After following Terry’s marvelous repair process I finally received the computer. Thanks Terry. I was still getting sporadic garbage on the screen. Typing out all the characters, I was able to see that some were shifted. Something was being held high:

A -> I    01000001 -> 01001001

B -> J    01000010 -> 01001010

C -> K    01000011 -> 01001011

D -> L    01000100 -> 01001100

E -> M    01000101 -> 01001101

F -> N    etc...

With the help of Terry and some EACA forum members (Leslie Ayling) I was able to narrow the area of issue to Z26 (74LS174) Pin 4 which is the input for Bit3. However I was not able to actually find any problems. After some playing around I noticed that flexing the video board causes the problem to come and go. That means there is a cold solder joint some where. Looking at the solder side of the board I saw that the manufacturer has used very little solder in general, and at a glance there could be multiple cold solder joints. I decided to reflow ALL the solder joints just to be on the safe side...this took me about 2 hours!!!!. Unfortunately in the process I snapped some wires on the brittle interconnect cable. Instead of trying to fix the broken cable, I decided to find a better solution. After much pondering (and conversations with Peter Nield) I struck upon a solution. I removed the old connectors, and installed strips of 32 pin SIP sockets. I then used 32 x 70mm jumper wires to connect them together. The jumper wires snapped firmly into place, and the machine fired up perfectly. So far the character issue has not returned.

FInally the machine seemed to be woking great.

This computer was recently won in an online auction by Terry Stewart. As Terry knew I had been looking for a System 80 for a while he was kind enough to offer to use the two ratty machines he got to create one bare bones system for me by swapping around parts. These machines in particular hold a special place in my heart as I used to attend Waiopehu in 1986 and 87, and used to use these exact machines when I was 16 years old. What are the odds!!!

What follows is Terry’s progress on fixing this machine and comments to me via email. You can see more detail on his blog here.