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Need help: TRS-80 Model 4 CRT display issues

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Just wondering if any body had an idea what wrong with the display on this TRS-80 Model 4 I just got yesterday.

While I've played with electronics all my life, CRT's are a little out of my league. I'm wondering if it's a bad capacitor or something. some times it fast rolls, the weird diagonal lines are always there as you can see in the video.

I haven't test the floppies yet, got to get some Model 4 boot disk.. which could be a challenge.

 

https://www.youtube.com/watch?v=hA82fPno-6o

 

 

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It looks like you have the brightness setting turned all the way-up; that may be why you are getting the lines in the background. It's been about 30 years since I touched a Model III (in elementary school :)), but I seem to recall a similar "problem". There should be a small roller under one side of the console to make this adjustment.

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Yeah, I seem two remember TWO roller knobs on the left-hand side under the keyboard. One was for brightness and the other contrast *IF* I remember right.

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yes, the brightness ad contrast are tucked away under the left side. Which i think was a good idea, easy to get to, but out of the way. I can turn the brightness does to the point the lines can't be seen, but want to know if this is a problems or a normal quirk. the scroll I'm thinking is either potentiometer not making perfect cont or maybe a weak capacitor somewhere. I can certainly handle replacing a cap or two if that's the issue.

 

I contacted a local TV repair shop that things it's be $150-200 to repair the "horizontal unit" or $50 estimate fee if they can't find a problem.. ack. only paid $90 for the whole computer.

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yes, the brightness ad contrast are tucked away under the left side. Which i think was a good idea, easy to get to, but out of the way. I can turn the brightness does to the point the lines can't be seen, but want to know if this is a problems or a normal quirk. the scroll I'm thinking is either potentiometer not making perfect cont or maybe a weak capacitor somewhere. I can certainly handle replacing a cap or two if that's the issue.

 

I contacted a local TV repair shop that things it's be $150-200 to repair the "horizontal unit" or $50 estimate fee if they can't find a problem.. ack. only paid $90 for the whole computer.

 

That indeed was normal. Actually that was a question I was asked more than once, having formerly been a Radio Shack computer marketing manager back in the mid 80's.... back when Radio Shack was still a company worth working for. Pity what they've become.

 

I'd try some of the proper cleaner, if it works, it's a temporary fix but you'll know what the problem is and can replace the old variable pots. DO NOT USE WD40!

 

dscn9865.jpg

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That indeed was normal. Actually that was a question I was asked more than once, having formerly been a Radio Shack computer marketing manager back in the mid 80's.... back when Radio Shack was still a company worth working for. Pity what they've become.

 

I'd try some of the proper cleaner, if it works, it's a temporary fix but you'll know what the problem is and can replace the old variable pots. DO NOT USE WD40!

 

OK, great, one worry down then, I kind of though the diagonal lines might be an video artifact, I've seen some many model 4 show them.

 

I'll go see if I can find some good contact cleaner to the horizontal hold tomorrow. The last contact cleaner I bought works.. but attacks plastic big time... I have never even used WD40 :) I haven't noticed the horizontal hold knows, are the on accessible from inside?

 

And I agree, Radio Shack isn't what it use to be, long gone from Canada, it's successor "The Source" is just a over priced consumer electronic store with clueless staff..

 

I once had a job offer from one of the Tandy Computer Center stores, but came down with a nasty flu and ended up having to pass on the job... It was sooo disappointing..

Edited by Atari-Collector

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Just an update.. after being a bit under the weather lately, I just got the urge to open up the Model 4 and check it out. Firsi I notice the warranty seal had long ago been breached.. but once in side all seems on.. I bought some good contact cleaner last time I was out and gave the brightness, contrast and horizontal hold pots a blast. Results are no jitter effect when adjusting the brightness and contracts now, and the horizontal rolling has stopped. :grin: :)

 

I also took a bunch of pics for future reference of the insides. and looked at all the capacitors, no signs of leaks or bulging. of course back then these machines were made they used the good parts from the start. I've finished cleaning up the case, and withe the exception of a couple minor marks on the bottom and back, I'd give it a 9 out of 10 for looks:) No to just get some DOS boot disks...

 

I've got some disk Images, and just have to figure out the writing with a old DOS PC part now..

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DOS BOOT DISKS?

Consider one of these instead... SD_HxC_Floppy_Emulator_RevF_TRS80_002s.j

 

I have one on my model 1 already, and it may be a better way to go since I still don't know if model 4's drives work or not.. how do you have it cabled inside? the drive below it doesn't quit look like a TRS-80 drive...?

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Another follow up. The contact cleaner on the horizontal hold fixed that problem. But a new problems has shown up while the arrival of DOS disk for my Model 4, Soon as it goes to boot from floppy the monitor goes nuts. I did a quick video to show what it's doing.

 

I suspect it's the power supply needing new capacitors to handle the extra hold of the drive starting up, but I'm open to suggestions.

 

https://www.youtube.com/watch?v=c3h5oAgDQbo

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time for a cap kit! for the monitor. that's horizontal sync problem. and a cap kit should fix it.

 

when your cap's get old the dieletric inside dries out and the caps will actually pull a power supply voltage low.

and cause all kinds of issues, possibly even buring up components because of the increase current caused from low voltages.

 

fix it now before something else goes wrong.

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Guess I forgot to follow up on this, the problem has been fixed now. It was just in the 80 column mode, and a simple adjusting to the variable cap (C210) that controls that fixed it, it's working normally now. (got the info on the TRS-80 group on yahoo..)

 

I have done an almost full recap on the power supply, wrote the quantity done wrong for a couple sizes, by it's 95% all new high end caps now on the power supply.

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