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Model 16 8" Drive diagnosis & repair?

K

k0d3g3ar

Experienced Member
Joined
Oct 30, 2011
Messages
111
Location
Scottsdale, Arizona
Well I just took delivery of a Model 16 with 2x 8" FDDs in it. Although I'm furious with the eBay seller who literally packed this unit to be destroyed by shipping (I've got some serious case repair work to do here), I was able to get it booting and it comes up with the "Insert Disk" message nice and centered on the green screen.

However after trying about 10 different Model 16 and Model 2 boot disks with TRSDOS and CP/M, it seems that this machine is refusing to read a disk. The disk light comes on with any restart, but there isn't the familiar clunking sound of the disk arm & motor movement that I have on my Model II.

So I'm asking a general question to anyone out there who has done this.... What is the best way to diagnose an 8" FDD? I could just switch drive A & B around, but the fact is that I'll still end up with one of them that is DOA. I'd like to see if this is just a matter of an electronic repair, or possibly a seized drive arm?

Does anyone have any specific approaches they have used to repair one of these?

Myles
 
What is the screen showing when you pop in the disk? I had a similar issue on my Model II where all of a sudden it would no longer boot up any disk. It turns out that I needed to reseat my memory cards. The 64k memory test on startup was failing so I just got a blank screen and no disk activity after inserting a disk. Once I reseated the memory cards then everything was back to normal. Also, the thin line drives on the 16 will not clunk like the big old full sizers on the Model II.
 
pski said:
What is the screen showing when you pop in the disk? I had a similar issue on my Model II where all of a sudden it would no longer boot up any disk. It turns out that I needed to reseat my memory cards. The 64k memory test on startup was failing so I just got a blank screen and no disk activity after inserting a disk. Once I reseated the memory cards then everything was back to normal. Also, the thin line drives on the 16 will not clunk like the big old full sizers on the Model II.
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Thanks for the info. There really isn't any noticeable change when I insert a disk and close the drive door. It is working like this:

1. Turn on the computer
2. Green screen comes up (inverse - black text on green background) states "INSERT DISK" (or similar - can't remember the exact message here but you get the idea).
3. Drive A red led is lit
4. Insert disk with label side to the left
5. Close drive door

NOTHING

Then if I try resetting or power on with the disk already in place, and drive door closed, red light comes on, green screen as before, no booting of disk.

I'm listening carefully for the noise of the FDD spinning or the head arm moving, and nothing at all. Its like its not being controlled by the computer yet the computer is turning it on with the red led lit on bootup.

Myles
 
Pull the "A" drive and inspect the PCB. These model 16 half-height drives have a tendency to blow the 7812 TO-220 voltage regulator. Mine was also equipped with a microfuse in the +24V line. The problem turned out to be shorted cap on the +24 volt line. I'm trying to remember the floppy model; I think it might be a Tandon TM848.

Terrible design, but fixable--and displays the exact symptoms that you see--LED on, but no motor spinning.

Alternatively, you can just swap the A: and B: drives, resetting the drive select jumpers.
 
Chuck(G) said:
Pull the "A" drive and inspect the PCB. These model 16 half-height drives have a tendency to blow the 7812 TO-220 voltage regulator. Mine was also equipped with a microfuse in the +24V line. The problem turned out to be shorted cap on the +24 volt line. I'm trying to remember the floppy model; I think it might be a Tandon TM848.

Terrible design, but fixable--and displays the exact symptoms that you see--LED on, but no motor spinning.

Alternatively, you can just swap the A: and B: drives, resetting the drive select jumpers.
Click to expand...


Thanks so much for the info, Chuck. Sounds like exactly what I'm seeing. I believe these are the Tandon drives too. I'll post back what I find.

Regards,
Myles
 
I hope this wasn't that "new old stock" one that I saw listed recently. It looked really pretty, and it'd be a real shame for it to be damaged by bad packing.

I also had a bad drive in my Model 12 that was dragging down the power supply. In my case, it was a shorted input filtering cap on the bad drive instead of the regulator itself.

I suggest also looking at the computer power supply before it sees too many more electrons. My Model 12's supply had some of those Rifa brand paper-dielectric EMI filtering caps. I learned all about their evil influence when one of them lit up. Luckily I was standing right there to hear the zorch, smell the burning paper smell, and yank power right away. I now replace them on sight with better poly-film EMI filtering caps.
 
NF6X said:
I hope this wasn't that "new old stock" one that I saw listed recently. It looked really pretty, and it'd be a real shame for it to be damaged by bad packing.

I also had a bad drive in my Model 12 that was dragging down the power supply. In my case, it was a shorted input filtering cap on the bad drive instead of the regulator itself.

I suggest also looking at the computer power supply before it sees too many more electrons. My Model 12's supply had some of those Rifa brand paper-dielectric EMI filtering caps. I learned all about their evil influence when one of them lit up. Luckily I was standing right there to hear the zorch, smell the burning paper smell, and yank power right away. I now replace them on sight with better poly-film EMI filtering caps.
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Thanks Mark. I took a look at the PS immediately after taking the cracked case off it, and has never been recap'd so I have to replace out those paper caps. I have a few replacements spare from doing this on a Model II a few months back.

This was not the unit you are referring to, but it is indicative of why I try and avoid buying from eBay. This seller was particularly negligible and downright rude about the whole sale. As soon as I closed out the auction and paid for it, I sent the seller a personal message stating "Please pack this VERY carefully because its going into a museum". I also offered to pay extra for shipping to ensure its safety. He never replied at all to my message. What I did get was an automated notice from eBay that the unit had been shipped.

Yesterday my wife calls out to me that my computer arrived, but she didn't sound too excited stating, "You better take a look at this". What arrived was a thin cardboard box - the ones you get for moving from uHaul. The box was completely ripped apart, split entirely down one side and you could see thin bubble wrap sticking out - the kind you would use to wrap a small Hot Wheels car - not anything suitable for a vintage computer. Of course, I got my dolly truck and carefully moved it into my workshop.

See the photos attached as to how it arrived. This unit was in perfect condition before it was sent.

If any collectors here need reinforcement of the dangers of eBay auctions, this should be your wakeup call. Sellers don't give a (*&#$ about these computers. They are just junk that they want out of their garage and its rare to find any that give two hoots about the deal. This was clearly the case with this seller.

I'd send it back to him and get money back, but before I decide the best way to address this, I wanted to first see the electronic condition of it. Despite the smashed case, the electronics don't look too bad. I may be able to reconstruct the case. They have some great laser cutters and 3D printers at our local hackerspace, and if I can paint match it, I *might* be able to bring back some of the aesthetics.

Myles

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It should be a crime to pack like that. I still cry for the 6000 case that literally shattered which I posted about a few months ago. Myles, the 3D printing approach is interesting. I have a few cases of the big TRS-80s that need work. Maybe we can eventually create replacement cases using this method. I'm going to look into it.
 
pski said:
It should be a crime to pack like that. I still cry for the 6000 case that literally shattered which I posted about a few months ago. Myles, the 3D printing approach is interesting. I have a few cases of the big TRS-80s that need work. Maybe we can eventually create replacement cases using this method. I'm going to look into it.
Click to expand...

I can definitely fix the case. The question is just how aesthetic I can make it look once its done. The wonderful advances in technology for paint matching, 3D printing, laser cutting, etc. should help a lot. I only have access to 3D Printers that can do small (e.g. 6" square) size items, but I think the laser cutter that I have access to should be able to allow me to cut replacement pieces that fit perfectly with any holes left. I kept all the pieces that were intact so that they can be glued back in, and I'm hopeful that super glue can do the trick with this.

I watch a lot of those shows on TV of guys that restore old cars and what they have to work with. Although this is a crime what the seller did, the fact is that compared to restoring a rusty Model T Ford, this shouldn't be too hard with today's tech.

Myles
 
At least the CRT arrived in good condition. That's a big problem with shipping these days.

The quality of case construction of the Model 16 never impressed me--it's too thin and probably should have been done in high-density structural foam.

At any rate, given some epoxy resin, some fiberglass cloth and maybe a little Bondo, you can probably restore the case to its original shape. Add some primer and paint and you're good to go.
 
The build quality of Tandon floppy drives was always horrible (materials and workmanship). I especially didn't like the fact that they used white color insulated wires for all of the wiring. Tracing one of the numerous electrical problems on the drives was always a challenge.

Early Tandon 1/2 height 8" drives were the same depth as full height drives and used a 110vac motor for the spindle (same as a full height drive) with the spindle motor running contantly. Later Tandon 8" 1/2 height drives had shorter chassis, and dc spindle motors.

I swore off working on Tandon 1/2 8" drives back in the 90s, and sent the junker I was using for parts all to the scrapper. I would say your best bet for getting two working drives that will generate disks that can be interchanged would be to buy another drive, and send the two drives out to be serviced, and hopefully one drive can be made to run from the two. When you get the working drive back, you can do a careful interchange test with your remaining drive to get a better idea of it's alignment status, OR send it in for servicing. From what I remember, for every ten tandon drives that came in for repair, only about one or two could be serviced and returned to 100% functional condition. Bad logic boards, bad wiring, and bad head assemblies were all problems.
 
Somebody rebranded YE Data YD174's as their own for an 8" half-height drive. Was it Tandon? Or maybe Qume? I don't recall. The YD-174s weren't too bad--they used AC spindle motors.
 
My experience with the Tandon 848 has been terrible. These drives are evil. Of the ones I have that actually look like they work, they will trick you. They work fine for awhile and then stop working. And they are ravenous eaters of Track 0. Just when you think you have one working well and you build up the courage to try to copy one of your rare, original copies of RS software...you get screwed as they munch your track 0. Did I mention they are the devil incarnate?
 
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