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Advice for repairing a TRS-80 Model III


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Bought a TRS-80 Model III for $15 at a yard sale today (the monochrome all-in-one, not the COCO). I can see a brief faint flicker when I turn it on but nothing displays. I did manage to get it to the cass? command prompt once but lost it after a few minutes. When I turn it off I see the display powering down (a vertical line and then a point of light that fades out - I think this is normal for this model of computer.) I've tried playing with the brightness dials and booting it up with the break button held down but that did not help. I'm thinking it probably needs capacitors to be replaced - likely on the power supply. Does anyone have suggestions about what the problem may be, and where I might be able to get replacement parts?

 

To be honest, I'd like to get the thing working if doing so is economical and to give myself some practice replacing capacitors on a machine that isn't worth much, but if that isn't possible I wouldn't mind using it as a display piece or passing it along as a fixer upper to someone who is more into this type of computer. I've played games on this model of computer back in the day, but it isn't exactly a Vic-20, Apple II, or Amiga. Just an interesting curiosity.

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I learned to program on one of those. You are correct that the monitor does normally wink then fade on the dot when turned off. Most mono monitors of the day did that. I would expect capacitors are the first thing to check. They provide the necessary boost to fire up the CRT. I expect the parts in that model are pretty cheap. It looked almost like a project kit when I worked on it in the 80s.

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I took a computer class in 8th grade and we used these machines. I'm dating myself but not as badly as it sounds - it was around 1989 or 1990 and even then they were ancient. We did some learning but mostly played video games of course. There was a very good lunar lander clone. Sadly, even if I get the one I got today working it doesn't have disk drives and cassette would be my only option. Realistically though, this was a business computer back in the day and today probably best at being a display piece...But I'd still try to hunt down the lunar lander game on cassette. :)

 

I learned to program on one of those. You are correct that the monitor does normally wink then fade on the dot when turned off. Most mono monitors of the day did that. I would expect capacitors are the first thing to check. They provide the necessary boost to fire up the CRT. I expect the parts in that model are pretty cheap. It looked almost like a project kit when I worked on it in the 80s.

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Hi, is this a cassette only model? I agree, starting with a power supply replacement or fix is probably the best bet.

 

As far as parts, eBay and there is a guy in Australia who restores TRS-80s and sells parts on eBay as well.. http://ianmav.customer.netspace.net.au/trs80/

 

Here is an example of a recent eBay sale of his: https://www.ebay.com/itm/152774684256

 

I've personally purchased several things from him, a fixed power supply, FreHD etc.. email him if you have questions.

 

There are several options available to you as a disk drive replacement etc... Some not so cheap of course http://bartlettlabs.com/and some a little cheaper https://www.ebay.com/itm/152574011423 http://hxc2001.com/

 

Here is a video of a Model III (diskless) working with a FreHD:

 

He has a number of helpful videos along with one on removing the cover of your TRS-80 so you don't break the CRT neck as mentioned below by Turbo-Torch.

 

Welcome to the club! I have a TRS-80 Model 1 and 4 myself.

 

Updated: to add a few more links

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You need to open it up (without breaking the CRT neck) and re-seat every IC and cable connection. Also spray some deoxit in the brightness and contrast pots. Keep in mind, it's an open monitor in there with stored voltage!

 

You also won't know if caps are blown until you open it up and LOOK. There will be at least one X capacitor on the power supply board and most likely it will be blown; although, it usually doesn't keep the unit from operating. Some board revisions have more than one X cap. If any are blown, it'll be obvious as they literally blow up.

 

There isn't much to go wrong in a basic 16K cassette based system. Unfortunately it's next to useless too as all the good software and games will require at least one disk drive and 48K. There's also the matter of getting programs to it. Unless someone added an RS232 board, the base model won't have one.

Personally, I download any of the thousands of programs I want off the internet to my modern PC and then attach my Model III to that PC with a null modem and save them to disk.

 

Someone has been selling NOS aftermarket disk controller boards on eBay for about $30 bucks. I've seen NOS RS232 board kits selling for around $50. You'd then need a good 180K or 360K 5¼ floppy drive and also a power supply from a disk based system...or simply add a separate power supply inside the machine.

The additional memory is just two sets of 8 pieces of RAM that plug in, super easy to bump it to 48K.

 

With some luck and a bit eBay searching, it's possible to turn it into a full blown disk based system for under $150.00.

If you don't have the skills or have little interest in the system, it's not worth it...pass it on to someone who can appreciate it.

BTW, the Vic-20 and Apple II are toys compared to a Model III.

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