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QumeTrak 842 stepper motor bad?

R

retrogear

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I just purchased a dual 8" enclosure and drives from eBay for my CompuPro. Both are QumeTrak 842's. One seems to work fine but the other never seeks backwards.
If I home the head to track 0 it reads the directory and will run a program but will not run the next one. It seems to never reverse seek. I've read on this forum that
the stepper motor is a notorious failure. The bearings seem ok because moving the head assembly by hand seems to be just as smooth for both drives. Anyone have
experience with this? Could this still be a bad stepper motor?

Larry G
 
Backward-vs-forward use the same windings, just activated in different order. See explanation here. Something is probably wonky in the driver circuitry unless there's a mechanical reason for the malfunction.

You are aware, of course, that motion is controlled by two signals at the interface--STEP/ and DIRECTION/. Could it be that you're not asserting DIRECTION/ ?
 
Chuck(G) said:
Backward-vs-forward use the same windings, just activated in different order. See explanation here. Something is probably wonky in the driver circuitry unless there's a mechanical reason for the malfunction.

You are aware, of course, that motion is controlled by two signals at the interface--STEP/ and DIRECTION/. Could it be that you're not asserting DIRECTION/ ?
Click to expand...

that's where I was going with my question above
 
Okay, but there could be a fault in the receiver for DIRECTION/; get that logic probe out and the maintenance manual and start tracing. The 842 is a pretty reliable drive--I've used one for many years.
 
The drive is currently J: and I'm on A: The direction pin 34 is sitting H but when I do DIR J: it is pulsed L for a very short period. Would the track0 sensor cancel the seek toward spindle during the read?
I get 0V on T0 sense at track home but only 1.3V when not home when I'm supposed to get at least 4V. I suppose getting another sensor would be close to impossible.

Larry G
 
Damn - that's it. If I put my lamp near the track 0 sensor, then DIR seeks back and reads !!! Anyone have a spare T0 sensor they can sell? I wonder if I can lower the resistor in series with the LED to brighten it up a bit ...

Larry G
 
It was mentioned in there what I'm thinking. It looks like my write protect sensor is the same so I could exchange them. Since the light is weak and write-enable blocks the light, putting a weak sensor in the write-protect would cause it to be write enabled
so I just have to not be stupid enough to try to write to a master disk. I did find this one at DigiKey so will order it eventually and see if it works.
https://www.digikey.com/product-detail/en/OPB880T55Z/365-1757-ND/1637401

Larry G
 
Larry,
We used to use the H21B3 Optic on some of the equipment. They were cheap and had a Darlington output.
If you could locate one of those It should work fine, assuming the mounting is correct. If I dig in a few
part boxes I may have a NOS SPARE.

I have the Fairchild H21B3 PDF if you want a copy.

https://www.newark.com/c/sensors-transducers/sensors/photo-interrupters/prl/results?brand=vishay
https://www.newark.com/c/sensors-tr...results?brand=tt-electronics-optek-technology
https://www.newark.com/c/sensors-tr...prl/results?brand=omron-electronic-components

Larry
 
Last edited:
Thanks Larry K

I found a batch of H21B3 on ebay which I can get in a few days. I'll give it a try. Darlington would have higher gain too. Those look like wires for PCB holes but I suppose soldering wires onto them would be easier than feeding new
cable which it looks like they head into a 30 pin plug.

Larry G
 
I can confirm the Fairchild H21B3 works good as a track 0 sensor on the Qumetrak 842. I get a good 0 to 4.9V swing now and now I have both drives working !!!
The datasheet shows 1=anode 2=cathode 3=collector 4=emitter but the new sensor was labelled corresponding + E + D which was confusing. It turns out the diode is actually called a light (E)mitter
so red+ was anode, black(E) was cathode(ground), white+ is collector and green(D) is emitter - wow. I'm just glad I didn't get 5V on anode and ground on cathode would be like shorting the 5V supply ...

Larry G
 
Larry G,
Good Deal! And now you have several SPARES. I also ordered some of the H21B3's because they work
very good. I'll have them in my stash.

Larry
 
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