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Strange Problem with a 1050...


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#1 DavidMil OFFLINE  

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Posted Sat Apr 20, 2019 10:25 PM

I have three 1050 drives.  Two work beautifully and the third one works fine except:

It will not format disks with DOS 2.5.  It formats fine with MYDOS and the other two

drives can read disks that it formats and writes in MYDOS, but it can't format in DOS

2.5.  If I format the disk on one of the other drives, I can then read and write to the

disk in the third drive without any problems, and both of the good drives can read

what the third drive has written without any problems.  I also ran the 1050 CPS disk

several times through the test loops without any problems.  I'm stumped.

 

DavidMil



#2 Nezgar ONLINE  

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Posted Sat Apr 20, 2019 10:33 PM

Reading this, I think of a past post by tf_hh "HowTo: Adjust analogue part of FDC 279x in a 1050 disk drive" about the
 
http://atariage.com/...050-disk-drive/
 

 

The typical issues:

 

- When the adjustment is absolute out of specs, you can´t successfully format or write to any disk. Reading might be okay

- When the adjustment is nok ok, but not totally worse: Formatting and writing a disc with medium/enhanced/double density fails, but single density works

- At all cases: You might can write format and write a disc with medium/enhanced/double density flawless, but no other drive can read your formatted discs...

 

The symptoms seem to partially match, but you indicate you can still write to the disk in the 'bad' drive after formatting medium/enhanced/double density in another drive...

 

Was the mech swapped to that drive/motherboard from another drive?



#3 DavidMil OFFLINE  

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Posted Sat Apr 20, 2019 10:40 PM

Was the mech swapped to that drive/motherboard from another drive?

 

That brings up a good point,  Let me swap the drive mechanisms with one of the good drives and

see which part the problem follows.

 

Thanks,

David



#4 Nezgar ONLINE  

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Posted Sat Apr 20, 2019 10:46 PM

Looks like you'd need a good oscilloscope to measure the 3 test mode frequency pulses being provided to the FDC chip, for potential adjustments to TP10, TP11, and R3. Write precompensation output (pin 31) / TP11 affects double density, MFM mode.

 

Re-reading tf_hh's post, the concern isn't if the MECH was changed but if the FDC chip was changed (WDC 2793 or WDC 2797). Those three adjustments are factory tuned to the FDC chip originally installed on the PCB.



#5 DavidMil OFFLINE  

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Posted Sun Apr 21, 2019 10:29 AM

Well, I'd have lost money on this bet...  I was sure it was an problem with the transport, but when I switched it with one of my

known good 1050's it worked beautifully.  And the problem stayed with the printed circuit board.  So I pulled the metal housing

off and found an Hitachi HN462732G EPROM with a sticker that said, " TANDON REV K".  The Controller is a Western Digital

WD2733PL-02.  I've included a couple of pictures.  I'm open to suggestions here?

 

DavidMil

Attached Thumbnails

  • 1050A.JPG
  • 1050B.JPG


#6 Nezgar ONLINE  

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Posted Sun Apr 21, 2019 7:53 PM

Are you sure the WDC is 2733? It should be 2793 or 2797. In your pictures I can barely make out anything on that chip, I presume you're having similar difficulty. It's probably 2793, since 2797 only works with ROM rev L...

2732 eprom should be fine... it's working with single density so I'm not concerned about the ROM. couldn't hurt to try a Rev L, but unlikely it will make a difference.

The issue only impacting DD still points to the 3 adjustments I mentioned previously being out. You could try the WDC 2793 chip from another PCB to see if it helps, but make sure to put it back in it's original PCB after since the adjustments on the PCB are tuned to the chip originally installed.

#7 Nezgar ONLINE  

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Posted Sun Apr 21, 2019 10:12 PM

The Controller is a Western Digital WD2733PL-02.


So, looking at your picture and comparing to a chip of mine, the top line of yours is definitely "WDC'82"
But the rest is illegible... Can you confirm?
WDC'82.jpg
 
A similar chip in a drive of mine reads: WD2793A-PL02
2793_nezgar.jpg
 
I wonder if it's possible to measure the variable capacitor value to compare between boards. The other 2 trimpots may be easy with just a multimeter to read resistance... Just to see if one of them are way out of whack compared to another drive.
 
An excerpt from the 279x datasheet that coroborates tf_hh's 1050 specific additions:
279x_adjust.png
 
Also mentioned on that thread how most people have found 1050's configured with a 230KHz data rate, rather than the 250Khz suggested in the datasheet, plausibly due to the reduced RPM 288 vs standard 300...



#8 E474 OFFLINE  

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Posted Mon Apr 22, 2019 1:32 PM

Hi,

I did this with an old analogue oscilloscope, but it was right at the limit of the oscilloscope's sensitivity. In the end, I took photos of readings from a good drive, and adjusted the suspect drive until it matched. This seemed to work.

#9 E474 OFFLINE  

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Posted Mon Apr 22, 2019 1:32 PM

Hi,

I did this with an old analogue oscilloscope, but it was right at the limit of the oscilloscope's sensitivity. In the end, I took photos of readings from a good drive, and adjusted the suspect drive until it matched. This seemed to work.

#10 DavidMil OFFLINE  

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Posted Tue Apr 23, 2019 4:02 PM

Are you sure the WDC is 2733? It should be 2793 or 2797. In your pictures I can barely make out anything on that chip, I presume you're having similar difficulty. It's probably 2793, since 2797 only works with ROM rev L...

2732 eprom should be fine... it's working with single density so I'm not concerned about the ROM. couldn't hurt to try a Rev L, but unlikely it will make a difference.

The issue only impacting DD still points to the 3 adjustments I mentioned previously being out. You could try the WDC 2793 chip from another PCB to see if it helps, but make sure to put it back in it's original PCB after since the adjustments on the PCB are tuned to the chip originally installed.

 

I answered this yesterday but my post seems to have disappeared.  Who knows, maybe I forgot to POST it after I finished.  I used a large magnifier and

a set of 6x glasses and I can barely see that it is a 2793 chip.  Since then I found the problem to be in the controller chip.  Suspecting that the problem

was the EPROM Rev K, I swapped it out first but nothing changed.  So I swapped out the controller with a 'new' chip from Best and the drive formats fine

except it was is having problems reading disks it didn't write and the other drives have problems reading the disks it formats.  I took the rev L chip out and

put the rev K back in and it is better but still having problems reading the outer tracks of disks written by other drives.  I'm guessing it needs to be realigned

now? 

 

David



#11 Nezgar ONLINE  

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Posted Tue Apr 23, 2019 5:15 PM

...it is better but still having problems reading the outer tracks of disks written by other drives.  I'm guessing it needs to be realigned now?

 

By 'outer' do you mean tracks 0-19, or 20-39?

 

Write pre-compensation for MFM (double density) operation only kicks in on tracks 20-39 to "pre-compensate" for the increased physical density on the inner tracks.

 

To me that behaviour further supports that the write precompensation variable resistor is too far off spec from 230ns... It's adjusted at R3, and measured at TP11 (pin 31 on the WDC controller)

 

It could also be that your other drive is out of spec, causing the disk to be not readable in this one...



#12 DavidMil OFFLINE  

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Posted Tue Apr 23, 2019 11:56 PM

 

By 'outer' do you mean tracks 0-19, or 20-39?

 

Write pre-compensation for MFM (double density) operation only kicks in on tracks 20-39 to "pre-compensate" for the increased physical density on the inner tracks.

 

To me that behaviour further supports that the write precompensation variable resistor is too far off spec from 230ns... It's adjusted at R3, and measured at TP11 (pin 31 on the WDC controller)

 

It could also be that your other drive is out of spec, causing the disk to be not readable in this one...

 

20 to 39.  But there is something very wrong with that CB.  Many chips and resistors and the larger electrolytic caps start getting very warm to darn right hot

if the power is left on for awhile.  I'm going to have to see where all that current is coming from.  Maybe a bad vreg.  The power supply is good as I've been

using it on my 850 for some time.  I hope it hasn't damaged anything else.  I'll let you know.

 

David



#13 xrbrevin OFFLINE  

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Posted Wed Apr 24, 2019 12:24 AM

the modern drop-in replacement "switch mode" voltage regulators work well in 1050s - really keeps the heat down!

(theyre also known as "buck converters", but i would advise against the variable output voltage types)



#14 DavidMil OFFLINE  

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Posted Fri Apr 26, 2019 3:55 PM

Ok, here's what I have currently...

 

U2 and U3 were getting so hot that when I wet my finger and touched them the moisture started to bubble.

Also U7 (the 6532 chip) was very hot.  Placing the 6532 chip in another drive yields a dead drive till the original

6532 chip was reinstalled (but no heat).  The controller chip seems to have been damaged too.  R56 was also

very hot!  With those four chips removed nothing gets hot and I'm getting a rock steady 12V and 5V from Q8

and Q7.  I've ordered replacements from Best and I've socketed U2 and U3 so I'm going to try replacing the four

chips (starting with U2 & 3) and watch to see what happens.  Could the stepper motor have a short that's drawing

all that current?

 

David



#15 1050 OFFLINE  

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Posted Sat Apr 27, 2019 6:48 AM

More likely you have the jack installed backwards.
Or somebody else did and that is what pooched the
U2/3 chips.

But the windings ohm out at 30ish for all four with
5 and 6 pins being common ground. Use an ohm meter
and find out if it's shorted.

It sounds like you've got your problem pinned down
at the very least and that's half the battle anyway.

#16 DavidMil OFFLINE  

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Posted Sun Apr 28, 2019 2:02 PM

R

 

More likely you have the jack installed backwards.
Or somebody else did and that is what pooched the
U2/3 chips.

 

 

When you say 'jack', are you referring to J15?  Remember that this drive worked ( well, mostly worked)

for awhile when I first tried to use it.  Then I could smell the burning and it's been dead ever since.  I don't 

think that removing the EPROM and putting a ROM in there for a few seconds before I remembered the

jumpers that needed to be changed would cause this problem.  With either chip in the drive it started  

heating up.  When I get the replacements for U2 & U3, I'm going to try turning it on with J15 disconnected.

(That's after I ohm out the stepper motor).

 

David  


Edited by DavidMil, Sun Apr 28, 2019 2:03 PM.


#17 DavidMil OFFLINE  

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Posted Sun Apr 28, 2019 4:56 PM

The problem is the stepper motor!  I pulled the transport out and plugged it into one of a good 1050.  As soon as I turned on 

the drive the stepper motor started vibrating back and fourth maybe a mm and everything started getting hot!  I guess the motor

started dying when I first discovered the problem and has now died totally.

 

Anybody know where I can get a MSAF200A91  Sanyo Part # 4Z26  12V DC stepper motor?

 

David



#18 1050 OFFLINE  

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Posted Sun Apr 28, 2019 8:35 PM

Yes, J15. You still could be still plugging it in backwards
from the times it did work right.

And my bad. Pin 5 and 6 of the jack goes to 12+ rail
not ground. Seems to be certain death for U2 is in
store if the jack is used backwards.

Can't imagine what could be wrong inside the motor that
would make it do that. Did you ever do the reasonably
careful thing and ohm it?

Short look for the number brought up only german eBay.
Doesn't look good for a replacement.

#19 Nezgar ONLINE  

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Posted Mon Apr 29, 2019 12:06 AM

Does the stepper manually turn? Either by plyers on the wheel itself, or moving the head by hand?

I know you previously said it was working but not on the higher tracks... I've received drives with steppers that were seized from years of non-use, but yours seems to have degraded *with* use...




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