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TRS-80 Model 4 Gate Array - half height drives retrofit issue

OS9dude

OS9dude

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Joined
Aug 6, 2009
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Location
Tucson Arizona USA
This past weekend I finally completed a project to bump up my Model 4 Gate Arraye (26-1069A) into what I call a "4D": upped its RAM to 128k and moved the floppies from a bad full-4D into this one. After successfully running tests on it with both LDOS 5.3.1 and TRSDOS 6.2.1 (AR), today when I fired it up to try my hand at updating LDOS 5.3.1 to take an expanded date in upon boot, I found that drive 1 begun to be reported as an illegal drive.

Booting DOS 6 I get a 'no drive' report in the upper bay drive. Looking inside at the slot, seems that the spindle is not spinning, the drive select seems to be working as I tried OUT 244,x with x being 1 & 2, each has the drive select light follow appropriately and while the bottom drive's spindle works, number two seems to be bad.

Already got a copy of the Sams Computerfacts papers for the Gate Array M4, just wanted to hear any words of wisdom from the community as I take a deep breath to open my M4 for surgery again :)


-- RP
 
TRS-Ian said:
did you take the floppy drive cable from the 4D as well?
Click to expand...

Yes. The original setup on *my* Model 4 had the full height Texas Peripherals drives, cable with the missing contacts. The whole updated setup was working OK 24 hours ago :-(

Noteworthy of mention: I installed the new Grafyx card on my M4, worked like a charm, that's when I was using drive :1 to store my BasicG creations yesterday; saved and loaded with no problem then.

FreHD is also just waiting for me to cook up a power supply for the board ;)


-- RP
 
Last edited:
Power is good to both drives. Confirmed that the motor spindle of that second drive is not working. The board of the FD is getting good power - confirmed, now I need to TS the power to the spindle motor. The drives are TEC FB-503, time to look for the documentation on these.

I know I have a 40 track DSDD drive somewhere, need to hunt for it - when found I'll drop it in the data and power connectors in the M4 cage to see how it behaves.

-- RP
 
OD9dude,
Check to see if that Model 4 has a Tandy Power Supply. If it does, remove the plugs on the Power Supply so you
can remove it and check for broken solder joints on the Pins. I've had several of those Supplies that needed to be
re-soldered, so the pins make a good connection. You should be able to see a small ring around the Pins if they
need the solder reworked.

It's worth a few minutes to check & Verify.

Larry
 
Turns out the TEC drive is at fault - still to determine what is wrong with it but it is centered around the spindle motor assembly, need to disassemble the thing and work on the parts more openly. The drive I could not find its stand alone documentation but a closely related model to it is well documented in the Model 100/200 Video Interface box - found the reference to that searching here in the forum :)

I have replaced both TECs with half height TEAC FD-55 I had from an unused CoCo box, the front end of the M4 looks weird with the openings left by the smaller bezel of the TEACs but it will have to do while I retrofit the TECs, the bezel on these would not go into the TEACs, I tried.

Minor issue was that I had to re-direct the ribbon cable to the motherboard to allow it to feed from the bottom up instead of up-down in the drives cage: the way the TEACs have their card edge oriented prohibited putting them as in the stock setup, unless I mounted the drives upside down, which I did for the initial tests.

Appreciate the suggestions here people, I read the forums every day and not only this one, it's a great resource to go back to for reference on issues past or for current support on this hobby.

Will update later with my findings on the TEC drive.

Cheers!

-- Rogelio
 
I may have two of these. Are these the same drives in the FD-500 enclosure? I'd be willing to part with one if that makes your appearance better. They work.
 
So here's where this project stands:

I dug up my yet to be used Model 100/200 Video Interface, thing actually has a TEC drive in it. Pulled it out and found it is a single sided version of this family of drives (Interface drive is a TEC FB-500). Tested it on the open M4 and it followed properly the drive select and the spindle motor turned on as it should, once everything neat and tied I find the new single sided drive :)1) has some issues tracking properly - this could be its original condition out of the Video Interface box, I did manage to get a proper DIR out of it but more often than not any access just fails.

I'll be giving it a rest for a couple of days - have opened and closed that M4 so much these past days that I am afraid I'll mess up something else. As I am to try FreHD on the M4, that drive 1 is not much of an issue, I'll troubleshoot the original double sided TEC to see if I can get its spindle motor running; from the quick observations I've done on it, the motor does not respond to the MOTOR ON signal (forced a low on it and no action seen - this worked on the other drives), so maybe I'm looking at a gate somewhere not following up properly.

:)

-- RP
 
Might be stepping too fast for the drive (lubrication). Knock it down to 30ms and see if it still has issues.
 
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