Subject: TRS-80 / System 80

From: Alan Greenstreet <[email-masked]>
Date: Sat May 3 05:50:00 2003

Hi All

I have just acquired a System 80 MkII (distributed in Australasia by 
Dick Smith Electronics).

On power up I get the LED power light ok but a screen full of random 
characters, the reset switch does nothing. I've had it apart and there 
are no loose connections or chips on the two main boards and no sign of 
any burnt or expired components.

Has anyone had similar problems and / or knows what the problem is?

Thanks

Alan

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From: "stephen johnston" <[email-masked]>
Date: Mon May 5 22:15:24 2003

-----Original Message-----
From: Alan Greenstreet <[email-masked]>
To: [email-masked]
Date: Sat, 3 May 2003 22:52:02 +1200
Subject: TRS-80 / System 80

> Has anyone had similar problems and / or knows what the problem is?
check the power rails for good +5,-5 and +12
then check the 4116 ram chips.
when they fail they get very hot.

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From: "Mike van Bokhoven" <[email-masked]>
Date: Mon May 5 22:16:12 2003

Hi Alan (and the rest of the list),

I have the technical manual for the Dick Smith System 80 Mk I and II. It
includes technical data, troubleshooting procedures and circuit diagrams.
I'm in Auckland, New Zealand. Think this might be of any help?

Interestingly enough, it mentions checking the temperatures of the RAM (ICs
Z27 through Z34) as part of the official RAM troubleshooting procedure - hot
RAM -> "REPLACE RAM", apparently. Replacements are to be "4116 type Dynamic
RAM of 250 nS or faster, Dick Smith part number Z9310". And no, that part
number no longer appears in their catalogue... surprise!

Other possible causes are listed as
- bad power supply, especially the +12V rail.
- bad 0.1 uF bypass capacitors
- connection between CPU board and interface board damaged or unplugged
- faulty ROM or CPU

To reset the machine, apparently it's necessary to hold down 'Break' and
'Reset' at the same time.

Good luck! If you can't resurrect it and/or get bored of it, let me know,
I'd be interested in this machine, it'd be an interesting challenge to
repair it.

Mike.

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From: [email-masked] (Tony Duell)
Date: Tue May 6 17:33:09 2003

> RAM -> "REPLACE RAM", apparently. Replacements are to be "4116 type Dynamic

The Radio Shack technical manual warns you that a RAM with supply line 
shorts can get up to soldering-type temperatures, and that you should be 
careful touching the RAMs to detect a bad one...

> 'Reset' at the same time.

On a TRS-80 with a disk controller, this will cause it to ignore the disk 
system and run the ROM BASIC. It's the way to start up a disk-based 
machine (or any M1 with an expansion interface, which contains the disk 
controller) without a system disk.

-tony