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New acquistion - Tandy Enhanced TRS-80 Model II w/software

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gepooljr

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Joined
Dec 8, 2012
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Location
Las Vegas NV
I am the new owner of a Enhanced TRS-80 Model II - includes the 68K card and I have a huge collection of software. I powered the system on once just to make sure it worked... it does but the screen is out of sync. GIve the age, I would like to do a complete tear down and rebuild starting with the power supply. Does anyone have the Model II Service Manual? I have not been able to find it anywhere. I do have the Technical Service Manual, but I'm looking for detailed steps to do a disassembly. Thanks!
 
Oh wow, that sounds like a nice machine. I admit to a twinge of jealousy. ;P

They are a little difficult to tear down. There is a booklet at the URL that Pete posted that explains how to take them down, but I found that I needed to stack a bunch of 1/4" socket extensions together to get to a couple of the fasteners.

Beware of the fragile plastics. Very fragile plastics.

Does your keyboard work?

Do please post photos as you work on it!
 
That tool seems expensive, but since it can double as a ski or tent pole, it's not so bad an investment I guess. :3

Lacking a magna-tip socket of the appropriate size, I held the fasteners in the socket with electrical tape while I got them started, and then got rid of the tape once they were going right. It's not as bad as we're making it sound though. IIRC there were two that I had to take out with the long boy and one that I had to take out with a wrench because there wasn't room for a driver. The hardest part for me was getting the CRT lined up just right during reassembly, but that was more just fiddliness and OCD than difficulty.

What all software do you have? Anything that's not already in the archive?

Sorry for being so aggressive, heh. They're just such cool machines that I can't help it.
 
Thanks Pete! I just ordered the nut driver and will receive it in a few days. I will setup a thread when I start and post pics. I'm going to start with the Power Supply First; I can already see ancient caps that need to be replaced.
 
Lee... now that it's Labor Day, I'm going to start cataloging the software and cross check it against what Pete has imaged. My only concern is that I don't even know if the 8" Floppy Drive I have even works yet. If it comes to that, I'll be happy to ship out any disks to someone who can image them.

And a request.... when the re-write of DND is done... I hope you can compile a version that will run on the Model II :D
 
gepooljr said:
And a request.... when the re-write of DND is done... I hope you can compile a version that will run on the Model II :D
Click to expand...

I plan for the Model II to be the first 8-bit machine that I target. ;D Although I plan to target the Model 4, Apple II, and C128 eventually as well. Assuming it will fit on all of them.

The thing is, though, the Model II, 4, and C128 will all run CP/M, so I am tempted to just target CP/M and call that good enough for all the z80 boxen. Not chasing the Models 1 and 3, nor c64 or atari 8 bits because it requires at least 80col.

DOS will be most difficult. Have to make OpenWatcom play nicely with Gnu Make, something I have never attempted.

I shouldn't talk about such things before I do them, though. For me, the best laid plans always fall by the wayside as I chase shinier and shinier squirrels, and then I feel like I hyped vapor......
 
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Here is the picture of the unit. I think its in pretty good shape. I'm not sure how far I want to go with aesthetics (scratches, painting, etc). Right now, I want to clean it up nicely and replace as many of the discrete components as needed to keep it going into the future. Any advise/suggestions are appreciated.

TRS 80 Model II.jpg
 
All I've had to do to mine so far has been to (1) replace the main case and JB-weld the keyboard plastics back together (unit massacred by the shipping apes), (2) replace the keyboard foams using the texelec kit to get the keyboard functioning again, and (3) remove the RIFA capacitors from the power supply.

I was going to paint it, but apparently the paint has to be custom matched, so I decided to just leave it as-is. It certainly has "character".

Mine has the later-model FDC card with the unpopulated 34-pin headers. I was able to suck the solder out, solder headers in, and get a flashfloppy gotek working without a special 50-to-34-pin adapter board, although the jumper setting are a little hinky. I can give you more details if you have that card and want to go that route. Note though that the 24v lines on the power supply have to be loaded in order for the unit to power up correctly (ahh, switching PSUs...), so you have to either leave the 8" floppy DC cable connected even if you're not using it or artificially load the 24v line with a big resistor or something.

The floppy drive uses a 120vac spindle motor that runs continuously and is loud and somewhat aggravating. IIRC the fuse in the back only goes to the disk drive 120vac lines though, so you should be able to take it out to quiet the disk drive down without cutting power to the backplane and CRT. If/when I reinstall my 8" drive and start using it instead of the gotek, I intend to mount a switch in the front to turn the spindle motor on and off.

If you have the older FDC, I think there's a way that disks can be erased if you try to run the machine without the floppy terminator installed in the back, IIRC, so be aware of that (unless I am full of poo; I can't remember the exact details).

That's all I can think of that affected my Model II odyssey. They are extremely cool machines, although I am starting to get a bit annoyed with how inflexible the memory banking scheme is (although it's likely that could also be my own stupidity too).

PS: Looks like your keyboard still has all the paint on the front lip. Machine must not have been used much. :O I bet you'll still have to replace the foams though.
 
Ok... I cleaned up the Model II a bit and turned it on. The floppy drive motor came up but then pulsed on and off, as the motor was trying to come up to speed but experienced uneven amp flow. The monitor screen (white) tries to come up but is distored with wavy line. I am smelling something like burned caps. My diagnosis is the power supply is shot and needs to be recapped and possibly other circuits tested. Any thoughts?
 
The floppy drive spindle motor runs straight off 120 VAC; it doesn't go through the DC PSU board at all iirc. It should run constantly and never turn off. If it is intermittent, I would suspect a problem with the motor or the AC wiring. Since these spindle motors never spin down, it's entirely possible that the bearings are out and the motor is bad. If you find this to definitely be the case, I may have some parts laying around, maybe......

If you smell burning capactors, it's probably the AC line filter (RIFA) capacitors. AFAIK (I am not a PSU guy) their purpose is to prevent the PSU itself from putting noise back out onto the AC line; they don't have anything to do with the PSU's internal workings or the quality of the DC output. I have a bad habit of just removing them and running without them, although it probably causes some RFI that might interfere with old radios and analog TVs and stuff if you are into that side of vintage electronics too. It is certainly possible to remove them and safely run without them until your replacements arrive. Again, if you discover that your PSU has bad components for which there are no replacements available or isn't worth fixing, I may have an extra one laying around, although it would hypothetically be one of the older model ones that probably can't source enough current to run all your 68k boards and stuff......

I'm not sure what to think about the video issues. Can you post a photo or video? AFAIK the analog board is compatible with the ones used in the Model 3 and Model 4. I may have an extra one, but I don't think it works.

Do you have the equipment needed to check the DC output of the PSU for correct voltage and for noise? Take a magnifying glass and check the solder joints around all the input and output pins; mine had cracked joints on the output that had to be reflowed for reliable operation. Guess I forgot about that in that previous post.

If the power rails are all ok, I would start by documenting how everything is installed, then pull everything but the z80 CPU board, z80 ram, and keyboard/display cards, but still remove and reseat those three, try it, and then put cards back one at a time (floppy controller, hd controller, 68k cpu, 68k ram) until it doesn't work again. Keep in mind as you are testing that some of the bus signals are daisy-chained through the cards, so they have to all be next to each other for things to work right, but do put them back in the same order as you reinstall them.

Hope that helps. I don't actually know what I am doing, so I hope none of that is bad info. Take anything that Pete says as 1000% more reliable than anything I say.
 
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Tackle the PS first. Only once you are getting solid 5, 12, -12 and 24v should you go further. Some pictures of the internals would help. Btw, if you do have software that is not in the archive I would be happy to image it.
 
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