Starting repairing Control Logic Board for drive B

CAREFUL EXAM UNDER MICROSCOPE

I subjected the board to a careful examination under the stereo microscope, looking closely at every component and wire for signs of damage. I found a broken capacitor that sets the time constant for a one-shot DM96L02 thus disabling this timing pulse.

I also saw one electrolytic capacitor that looked a bit dodgy to the eye and applied a resistance test to it. Fortunately it passed the sniff test so it doesn't need replacement.

REPLACEMENT OF BROKEN CAPACITOR

The schematic gave me the value for the capacitor and fortunately I didn't have one at hand, so off to Anchor Electronics and, nine cents later, I had what I needed. I desoldered the old one and installed the new one, putting the board back into apparent full working order.

TESTING OF LOGIC BOARD IN DRIVE A

It malfunctioned in a slightly different way, but still rotated the supply reel for a few seconds at power up. It also failed to load properly since it couldn't reverse the direction of the reel for the first step of the load sequence.

So much for the unrealistic hope that everything wrong with the board would be visible as damage and easily corrected by replacement of a part. Real debugging ahead, tracing signals around the board until I find the defects.

It would be easiest to debug if I had a card extender, but I don't. I considered designing one and sending it to fab, as long as I can find the female connector into which the card is inserted.No luck finding a 35 x 2 row .156" connector at Digikey, but I widened my search. I did find a 36x2 connector of the proper spacing on eBay and given its low price, bought it.

When the connector arrives next week I will decide whether to build an extension board using this socket. There are other ways, a bit more cumbersome, where I can put micrograbbers on specific component pins/leads and slide the card all the way into the card cage.