View Full Version : TRS-80 Model 4 "Error in 255"

May 5th, 2007, 03:44 PM

I have a TRS-80 Model 4 that keeps giving me an "Error in 255" scolling down the screen when I turn it on.

I believe it is related to the keyboard - I think one or more keys are stuck?

Has anyone else run into this problem?

I posted in the marketplace to see if anyone has a replacement keyboard...


Terry Yager
May 6th, 2007, 08:38 PM
The 'Error in 255' message indicates an error in your BASIC program, in line 255. (BASIC programs require each line to be numbered). Apparently, your disk has a program set to autorun at boot time. Try hitting the 'Break' key when the error message appears. This should drop you out of the dysfunctional program and back to a BASIC 'OK' prompt. If you're boned-up on your BASIC, you can try and de-bug the program from there.


May 7th, 2007, 05:32 PM

This does not appear to be an error in a Basic program. The error occurs when I load the DOS 6.02.01 disk - basic is not in memory yet.

I think the ERROR in 255 is some sort of System error - like listed on this web page: http://home.iae.nl/users/pb0aia/cm/m2errors.html.

I think there is moisture in the keyboard that is drying out - today I don't get the Error in 255, but get some random letters displayed on the screen without me touching the keyboard.

I'm working on finding a replacement keyboard to see if it helps...

May 7th, 2007, 07:31 PM
I've had this type of problem with Model III/IV before and the simplest cure is to go to Radio Shack, get a can of cleaner/degreaser, take the key caps off, one at a time, give the contacts a quick shot, put the keycap on, punch it 5 or so times and move on to the next.

Do this with the computer off and leave it for a few hours. It's best to clean them all at once to avoid having to do it whenever a key gets flaky. Turn on the computer, and, if any keys are acting up, turn it off and give those keys another treatment.

May 7th, 2007, 09:25 PM
That is a really good idea - will give it a try this evening and see if it helps.

I have found that using an old dental pick that has a curved end on it works really well for removing the keys on the TRS-80.


May 8th, 2007, 10:03 AM
Yeah, that or the short end of a PC backplane cover.

May 8th, 2007, 02:53 PM
I removed all of the keys this morning and sprayed cleaner into each keyboard hole. I then put all of the keys back in.

When I got home from work this evening I powered it on and now I'm getting a "Disk Error". It looks like my DOS boot disk has stopped working. I'm not sure if the keyboard has improved or not...

Now I'm on a quest to find a replacement DOS disk for the TRS-80....

May 16th, 2007, 02:39 PM
The TRS-80 boot disks I requested from www.trs-80.com arrived on Tuesday. The TRS-80 boots up with these new disks, but the keyboard still has issues.

The enter keys are non-responsive and the keyboard always has the caps lock key on.

I removed all of keys and cleaned the interior of the keyboard with tuner cleaner from radio shack.

It looks like the keyboard has a mechanical problem and it appears that you can't really take the keyboard all the way apart to determine the problem.

So now my search continues for a replacement keyboard.

Please let me know if anyone has a replacement keyboard for a TRS-80 Model 4 that you would be willing to sell.

May 16th, 2007, 07:45 PM
You might want to try just resoldering the connections for those keys.

People used to pound them pretty hard and it could just be cracked solder joints.

Flip it over, find the keys you want (I think they were even silkscreened on the back of the circuit board) and add a bit of solder and let it reflow. There may be either two or four pins for each key, so, just reflow everything in the general vicinity of the key :)

July 6th, 2007, 02:57 PM
I finally have a complete TRS-80 Model 4 with a working keyboard. I discovered that the Model 4 has two types of keyboards. One keyboard has mechanical keys and the other type has plastic membrane.

I ended up purchasing three non-working TRS-80's off of Craigs list until I got a working keyboard.