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Myarc cards for sale/repair tips

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2 hours ago, Ksarul said:

Nice troubleshooting. . .

Thanks Jim.  I shut everything down after attempting to format the hard drive which ended in failure.  What bugged me is that my floppy was corrupted at the same time. So a few minutes ago I fired up the system and tried to write to the hard drive and floppy -- and corrupted both drives.  On a hunch I replaced my test bench 9234 with the owner's 9234 - and it now works!  Seems that my test chip bit the dust since the last time I used it.  I just finished formatting a MFM hard drive and a SS/SD floppy successfully.  To cover the bases I need to verify that the bad chip is indeed bad, since there could be a poor socket connection or some other flakey chip/solder joint that is the culprit.  (That has happened more times than I wish to count yet it is a lesson I sometimes must re-learn).

 

EDIT: Confirmed, sadly, my test bench 9234 will read data but cannot write without corruption &  locks on cylinder 0 during a format operation.  

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Sometimes the 'third time is the charm'.  Last weekend I replaced my defective test bench 9234 with the owner's 9234.  Everything seemed to work fine until I noticed that occasionally the HFDC would not load MDM5. I put this down as a fluke until I realized the problem was not limited to the hard drive.  The strange thing is that it only happened after I turned the PEB off for a few minutes.  When I turned on the PEB and tried to catalog a drive, the card would go out to the hard drive and lock.  Turning the console off and on resolved the issue.  I was able to repeat the process with similar failures; sometimes the hard drive light came on and locked the system, other times it would blink and go out to spin the floppy, then lock.  Tonight I checked the components for any obvious issues.  This card had been modified for 9+ heads (I reverted it back to <9 for use with my MFM drives) so I first thought one of the head-related chips was affected. 

 

I then remembered something from my earlier tests:  when my bad 9234 was in the system, I didn't experience these initial powerup lockups.  I replaced the owners 9234 with another chip and so far, so good.  I'm a bit skeptical this is the fix so my next step will be to tempt fate (and on a Chicago TI Faire weekend!) by testing the two suspect 9234s in one of my own cards. I may still opt to replace the some of the common circuitry to be safe, depending on the results.

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Skepticism is good.

 

I tested the bench 9234 (the one that corrupted my mfm and floppy drives during writes) in my HFDC.  To my surprise, the chip did not corrupt the drives.  I then tested the customer's chip in my HFDC; it did not lock up during the first access.  Just to be sure I wasn't dreaming I installed the 'bad' 9234 into the customer card, wrote to the hard drive, and the card immediately corrupted the drive. Two chips common to the floppy and mfm drives are U9 and U11.  I desoldered them and tested both in my HFDC with success.  I socketed the customer card and installed new chips - no change. I figured it was time to mull over the problem so I walked away for a while.  I then remembered that early in the repair effort I had not experienced the first access lockup scenario so I brought the card back to the woodshed workbench to take one last look at my work.

 

When removing the QIC-02 circuit chips and socket (U22, U23, U24, U32) the final step is to add a jumper on the back of the card, in the vicinity of the 8Mhz xtal. I had prepped the two through holes for a jumper and was about to install it when I got called away for a short while.  When I returned, I completed the rest of the work but failed to realize the jumper was missing. 

 

I initially dismissed the missing jumper as the cause of the 9234 problems. I could not fathom why three 9234s act differently in the same card. So I traced the two connections back to the gate array and 9234.  The two traces tie the  9234 Chip Select pin 16 to the gate array.  The 9234 datasheet states:  image.png.303be3d3a109b89f2673dcff597b6327.png

 

It isn't clear to me if this means the CS signal can be derived separately using either source.  Regardless, if pin 16 isn't tied to the gate array strange things can happen.  In my case, three different 9234 chips presented three different outcomes during testing:  corrupted writes, lockup on first access, and no problem .   As soon as I installed the jumper the card functioned normally with all three 9234 chips. 

 

I inspected a Rev 'C' HFDC card for the jumper and found a trace had been added to U32, between pins 9 and 12.  This is much safer and easier than installing it behind the xtal.  It also matches the Rev C board. 

 

The card tested fine with both a TI and Geneve system; CRC stress test showed no read/write errors.  I slotted the edge connector and now finally consider this card fit for return.

 

image.thumb.png.a74348d2f75eee46417e2bf8f5267e94.png

 

 

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I spent the rest of the afternoon working on what will be my new Geneve workhorse so that I can strip down my 20+ year always-on primary system.  

 

Before my 'break' I installed  DC-to-DC converters in place of the three 5v regulators. Today I only got so far as replacing the caps and some prep for the 192K video update because I decided it was time to try removing the 12v regulator and composite video chip from the card.  I have wanted to reduce the power load and eliminate the 12v at the video port.

 

Unfortunately removing the chip and regulator result in a black screen and no analog RGB.  I couldn't tell from the schematic WHY this was the case and since I really wasn't interested in messing around further I re-installed the regulator and chip, now the card is working as expected.   Next weekend I will add the 384K SRAM to the card by following Fabrice's and my instructions and prep the card to play with some Winbond chips Atrax sent me for the PFM512 modification. 

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