RFC: Testing/Burn-in proc for TRS-80/Tandy model 4/4GA/4D/4P (Suggestions please?)

[dracos]

Ok, so if I was going to declare a harvested, scavenged, or otherwise pieced together model 4x, "healthy", what procedures/testing would be best to do? Please include whether your suggestion is for all variances on the model 4, or specific to a sub-type.
I think this would make a good living/reference document.
I guess relevant categories would be:

Power Supply:

Video:

Diskette System:

Keyboard:

Expansion Connectors:

Hard Disk System:

Other External Devices:

 

[RetroHacker_]

Plug it in, turn it on, see if it works?

Obviously, check the power supply voltages - make sure that's working correctly. Format disks in both drives and swap them to make sure the drives read each others disks. Write some simple BASIC programs, make sure all the keys work, etc. For adjusting monitors, I usually fill the screen with lower case m's and adjust that to look good and legible.

We're not talking about a particularly complex computer here. Just use it - run programs, format, read and write to disks, etc. Leave it running a simple BASIC program that prints stuff around the screen for a few hours, make sure it doesn't lock up.

-Ian

 

[dracos]

Plug it in, turn it on, see if it works?

Obviously, check the power supply voltages - make sure that's working correctly. Format disks in both drives and swap them to make sure the drives read each others disks. Write some simple BASIC programs, make sure all the keys work, etc. For adjusting monitors, I usually fill the screen with lower case m's and adjust that to look good and legible.

We're not talking about a particularly complex computer here. Just use it - run programs, format, read and write to disks, etc. Leave it running a simple BASIC program that prints stuff around the screen for a few hours, make sure it doesn't lock up.

-Ian

Thanks, and that's all good common sense worth mentioning, was hoping for something more detailed and specific.
ie. Use voltmeter to check 12vdc at location X, Y and Z. etc.

 

[RetroHacker_]

Thanks, and that's all good common sense worth mentioning, was hoping for something more detailed and specific.
ie. Use voltmeter to check 12vdc at location X, Y and Z. etc.

I mean, I don't have a Model 4 right in front of me, so I don't know exactly where to tell you to test the power supply voltage, beyond the blatently obvious things like the disk drive power connector, or at the ROMs or DRAM chips on the motherboard. But that should be good enough - again, there's not that many parts in this machine. If you're getting proper voltage to the motherboard and the disk drives, there's not much else to check. I don't know the exact test points on the power supply itself, but you could always follow the wiring back and find them.

I suppose if you wanted to go all out, you could find the service manual and check the B+ in the monitor, and get a HV probe and check the output of the flyback... but if the monitor is working and you can get a good, stable, clear picture that fills the screen properly, then I wouldn't worry about it.

-Ian

 

[dracos]

Makes sense. I guess without a factory service manual it's a bit of an over reach.

 

[jltursan]

Yep, without real knowledge a service manual it's a bit overkill; so I agree that a good pair of eyes, simple tests and a lot of common sense are usually enough to give a good picture of how bad is a computer.

Usually if you have spare pieces, the fastest way to know if they're in working order is to swap them with the ones of a working machine. Of course it implies that you must have a fully working second computer. There's an exception, I think that PSUs are risky to swap; so I prefer to do some measurements with a voltmeter.