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TRS-80 15 MEG 26-4156 repair

VERAULT

VERAULT

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So In a recent pickup I got a TRS-80 15 meg hard drive with ribbon cables. IT was disgusting inside and out.. like a black soot or industrial grime. Seller said he didnt know anything about it or what it goes to but the unit has no power. First thing I did was scrub everything inside and out and clean the internal psu pcbs etc.

I put the unit back together for testing with a junky ide hard drive for a load and nothing. I am getting no voltages. I started probing for AC voltage and wasnt getting any. The units AC power comes in and goes directly to a relay before going out to the AC fan and a junction block to the psu. The unit had 3 indicator lamps: ACTIVE, PROTECT, and POWER. Only PROTECT seems to be a button you can push, the other two appear to be lamps.. which is strange because that means this unit has no power button. Unless I am missing something and the computer turns this thing on.

Anyway I opened up the relay and tested the winding, I thought I had a break but I am getting 169 Ohms across the coil. Here is a photo of the relay. If this thing doesnt engage it wont give ac power to the system. So what am I missing? Anyone have experience with these drives? ITs built like a tank, I am impressed with its construction.

IMG_20231102_144701.jpgIMG_20231102_150527.jpgIMG_20231102_150542.jpgIMG_20231102_150249.jpg
 
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That's a secondary unit. The relay needs 12v to allow the power supply to turn on. Thwe 12v is provided by the primary drive over the cables.
 
That is a secondary unit, once you get the power sorted you will need a Primary unit which has the HD controller and drive or add a controller to that one. The Primary units have a key switch on the front as the power switch.
 
Ok thanks guys. So my concerns about the computer needing to be present for this was correct. Thats kind of weird but good, glad we answered that.

Ok what can you guys tell me about this thing? Its complete with two ribbon cables for the rear. What TRS-80 machines are supported? TRS-80 classic models, COCO's? Tandy 2000 or 1000? Big Tandy? I have them all so which should I test with? What controllers are needed? Are there any TRS-80 computers that have the controller built in? Id like to know as much as I can about this machine.
 
Technically, you need a primary unit first. Something like this: Link
These work on the II, 3, 4, 4p, 16, 16b and 6000. I don't think there were adapters for the PC lines or the 2000. I could be wrong about the 2000.
There is a 50 pin cable that goes from the computer to the primary. There is a 34 pin and 20 pin that goes from the primary to the secondary that you have.
You should strap the secondary drive as DS1 and the primary should be DS0. (DS is drive select).
 
kb2syd said:
Technically, you need a primary unit first. Something like this: Link
These work on the II, 3, 4, 4p, 16, 16b and 6000. I don't think there were adapters for the PC lines or the 2000. I could be wrong about the 2000.
There is a 50 pin cable that goes from the computer to the primary. There is a 34 pin and 20 pin that goes from the primary to the secondary that you have.
You should strap the secondary drive as DS1 and the primary should be DS0. (DS is drive select).
Click to expand...
How is that any different than the one I have? It just looks like an older 5 meg version. The back of mine looks the same except I have a data in port too.

So I would have to buy another unit? I dont know if I want to invest more money for something I am not even sure works..


Why on earth would they make a hard drive that cost SO MUCH that couldnt even be used without first buying another very expensive hard drive?
 
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The one in the link has the key. It is a primary hard drive. It has an internal controller based on the 8x300 or WD1000 that converts the computer's 50 pin connector into an MFM drive interface. The one you have is a secondary drive. It expects a primary drive to control it and to send the 12v down the line to power it on. Think of the 50 pin connector as the ISA bus, the controller in the primary is analogous to the MFM controller you would plug into the ISA bus on a PC.

The stores usually didn't sell you a secondary unless they knew you already had a primary (at least the ones I dealt with) Here's the interal shot of a primary drive. Note that it has a card on the top with lots of connectors.
Tandy_Model1_InsideHDunit_s1.jpg

These systems would support up to 4 drives. One primary and three secondary for up to 280 megabytes of storage.
 
If the mfm drive fails can you replace it with any other MFM like an ST-225 or does it have to be the exact model.. (which was the downfall to apples' equivalent the 5mb profile drives which had a modified st-506 )?
 
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kb2syd said:
The one in the link has the key. It is a primary hard drive. It has an internal controller based on the 8x300 or WD1000 that converts the computer's 50 pin connector into an MFM drive interface. The one you have is a secondary drive. It expects a primary drive to control it and to send the 12v down the line to power it on. Think of the 50 pin connector as the ISA bus, the controller in the primary is analogous to the MFM controller you would plug into the ISA bus on a PC.

The stores usually didn't sell you a secondary unless they knew you already had a primary (at least the ones I dealt with) Here's the interal shot of a primary drive. Note that it has a card on the top with lots of connectors.
Tandy_Model1_InsideHDunit_s1.jpg

These systems would support up to 4 drives. One primary and three secondary for up to 280 megabytes of storage.
Click to expand...
That reminds me of the way my Kaypro 10 works. There's a parallel IO bus cable that does to a WD1002 board, and that has the MFM controller to the HDD. Of course all inside the Kaypro. Thanks for the photo!
 
kb2syd said:
That's a secondary unit. The relay needs 12v to allow the power supply to turn on. Thwe 12v is provided by the primary drive over the cables.
Click to expand...
So can I connect 12v across the relay to test the unit and psu? Directly jumping in 12v that is.. maybe via a battery pack.
 
VERAULT said:
So can I connect 12v across the relay to test the unit and psu? Directly jumping in 12v that is.. maybe via a battery pack.
Click to expand...
Yes. You can then use it in place of any MFM drive. You can also just remove the relay by taking the blue and bown spade connectors (circled in red) and plug them in to blue and brown on block after relay (circled yellow).
1699040836971.png
 
kb2syd said:
Yes. You can then use it in place of any MFM drive. You can also just remove the relay by taking the blue and bown spade connectors (circled in red) and plug them in to blue and brown on block after relay (circled yellow).
View attachment 1267318
Click to expand...
Ok thanks for this. Unfortunately the blade connectors on the relay are 3/4 the size of the ones on the bus bar. I snipped the corner of the busbar tab just to bevel it so the blade connector can make a connection. The good news is the PSU is good. I am getting 5.05 V and 11.78V. Using an IDE hard drive to draw a load.

I let it run for a while just to stabilize and check. Seems fine.

I thought time to try powering the dual height Tandon TM-503.

At first it bogged down the system so much the AC fan was slow to spin up, a few seconds later the fan got faster. Voltage was down to 11.39V. There is a tiny ferrous bead floating on copper at the bottom of the motor making contact with the pcb of the drive. I thought maybe it was corroded and not making a connection. Like points on an old car. I gave it a quick wipe and turned the system back on. Immediately the drive started to spin, slowly at first than faster until it was at full speed. The bearings are not happy at all. The noise has gone through various pitch changes but I want it to run to work the bearings. I will take the pcbs off and try and add a drop of oil to see if that will help. Anyway the voltages are back up to 5.05V and 11.58V with the tandon drive running for 20 minutes now.IMG_20231106_120352.jpgIMG_20231106_120757.jpg
 
So forget about the drop of oil I dont think thats possible if you see this motor. Strange thing it has this little magnet (yellow arrow) and a pin which i assume if for centering the spindle (red arrow)? Also the motor noise just spontaneously went away and it sounds like a regular MFM drive now. Although the 12V rail voltage hasnt changed (well it gets up to 11.6V).IMG_20231106_122325.jpg
 
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I guess this is the end of the road for testing as far as I can do. Im on the fence as to what to do with it now. I buttoned it all back up and I guess its off to sit on my shelf.
IMG_20231106_124352.jpgIMG_20231106_124719.jpg
 
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