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drpeter

1050 disk sensing problem- any ideas?

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Hi,

 

I'm hoping for help in resurrecting my 1050 drive.

 

I dug it out for the first time in several years and was pleasantly surprised when it fired up and booted from a disk without incident. Until I tried to do the same again 30 minutes later, since which time it has failed to  spin any disk. The busy light does not come on when the catch is flipped down and there is no evident attempt at activity with the stepper motor or drive motor. The drive belt is in place.

 

There is no problem visible to the naked eye with connectors, wires or components and connections on the main circuit board. I've tried reseating all the connectors nevertheless, to no avail.

 

The power LED is on and the power transformer measures correct voltage and works with other equipment.

 

Having downloaded the 1050 field service manual, I've made the following checks:

 

All the voltages in the power supply stage test as normal. However, there is no voltage to the drive motor (zero volts on the red wire whether drive door is engaged or not).  The resistances across the drive motor are normal.

 

The diskette sensor switch is operating correctly.  The voltages on the inputs & outputs of the diskette sensing circuit integrated circuit U6 also behave as expected.

 

However, on pin 11 of the PIA chip U7 the voltage remains at 3.2 V regardless of whether the door catch is open or closed. I understand that this voltage should fall to 0.1V when the drive is activated.  I have reseated the PIA chip, but no difference.  Short of swapping out the PIA chip for one from a known good drive, which I don't have, I've run out of ideas. Anyone out there able to help?

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I would jumper pin 11 of the 6532 RIOT chip (U7) to ground

for a short second to see if that does cause the motor to

spin up and the activity light to shine. And if so, then I would

go to eBay and order a replacement 6532 for six bucks and

maybe get some cheaper ones coming from china too. Just

in case the one you get over here isn't any good either.

 

It sounds like you have the culprit duly rounded up and caught

red handed too. 6532 is commonly problematic although this

exact symptom isn't the norm and a first IIRC here. Always a good

thing to have one as a spare.

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2 hours ago, 1050 said:

I would jumper pin 11 of the 6532 RIOT chip (U7) to ground

for a short second to see if that does cause the motor to spin up and the activity light to shine.

OK, so that worked- the drive spins up and busy light comes on with pin 11 grounded. So definitely not a problem further on than the 6532.

 

2 hours ago, 1050 said:

I would go to eBay and order a replacement 6532

Does it matter whether it's a 6532P or 6532AP, do you know? And does the second designation printed on the chip below that matter (which I presume is a revision number, e.g. 6532-11, which is what mine says) Most on-line chips seem to have 6532-13...

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14 minutes ago, drpeter said:

Does it matter whether it's a 6532P or 6532AP, do you know? And does the second designation printed on the chip below that matter (which I presume is a revision number, e.g. 6532-11, which is what mine says) Most on-line chips seem to have 6532-13...

That part of the designation won’t matter. “P” indicates a plastic package, “AP” (IIRC) is an “A” version of the chip, rated for 2Mhz or something. There’s not solid agreement on what the -dash number suffix indicates; some say it’s a revision, others (given how standardized the 65xx chipset really was and is), believe it to merely be a manufacturer’s line or lot number code, perhaps even identifying to the supplier which plant fab’d the die.

 

All of that is really irrelevant. Assuming the chips are good, any 6532 should work in this application. 

 

Just a heads up though - I bought a lot of NOS 6532s a few years ago. All were marked as Rockwell chips fab’d in Mexico as late also 2010, but 2 of the 5 were not fully functional. I was using these to repair a 2600 that would not recognize one of the difficulty switches. In the VCS/2600 design, those switches are read by the 6532. The chips worked fine in every other test but one of the input lines was dead. The other 3 in the lot worked fine. 

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OK, Thanks, I'll get a couple on order and report back in due course.

 

You guys are brilliant.

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