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TRS80 Model 4 Power Up problem

PostPosted: Sat Feb 23, 2013 8:15 pm
by TRS80
I decided my TRS80 Model 4's needed some attention and on powering up the first one I was greeted with a screen of random characters.

Not a great sign. Turned out the Z80 needed replacement. The fault finding steps are outlined on my blog at Likely a process many retro computing enthusiasts are familiar with but it shows how a few simple test tools really help.

Re: TRS80 Model 4 Power Up problem

PostPosted: Sat Feb 23, 2013 9:08 pm
by tezza
Good diagnostics. Thanks for writing that down.

Yes, I've had a couple of CPUs fail on me too.

Re: TRS80 Model 4 Power Up problem

PostPosted: Sun Feb 24, 2013 7:52 pm
by TRS80
Like so many things with retro-computing it only takes money :-) Ian Mavrik ( would be pleased to sell you one. I have been lucky to collect 2 Model 4's, a Model 3 and a Model 100 over the last 15 years.... most before collecting became popular.

Seriously though.... yes they are nice machines, particularly the Model 4 but not very common in New Zealand.

While my Model 3 and one Model 4 are stock configuration machines, the one with the failed CPU is definitely not.

I got it through Trade and Exchange in the late 90's and was staggered when I went over to pick it up because it was the machine that Bill Porter (the owner of Porterfield Computers... the Radio Shack agents) used for all his software development and I think subsequently sold to Basic Payrolls in Newmarket who did a lot of bureau payroll processing using TRS-80's in the late 80's. I worked for Porterfield as a holiday job in 1985/86 so had used the machine regularly.

It was very distinctive because the internal drives had been replaced with 2 x 80 track (Mitsubishi) and 2 x 40 track (Tandon TM-50). I think the machine was a US domestic model, imported before the 240v model was available and modified for NZ so the power supplies are after market Astec units and there are a number of mods to the main board and floppy controller.

I am refurbishing it at the moment and have replaced the floppy drives with two internal 3.5" 720kb units in the bottom bay which makes software transfer from a PC a bit easier. I will probably connect one of the TM-50's externally so I can easily write disks for the other machines. A full height hard drive frame in the top bay with an internal "SD Card" and interface board the emulates a Radio Shack hard drive.