Old Flex Card Repair

[Shift838]

So I was digging through boxes last weekend and found a old flex interface card with a post-it note that said BAD, not in my handwriting.  Guessing this came from my trip to Arizona probably 15 years ago when I picked up a slew of TI stuff.

 

I first opened it up to see if it had been modified for 5v only (nope all original).  Inspected all the caps, resisitors and ICs, which look good on both the card end and the side card end. All traces look good too. 

 

I then plugged it in to my test PEB by itself and no smoke.  so I plugged it in with a 32k memory card go into XB and it reports the correct memory expansion.  Nice..right.  

 

Well I remember reading somewhere that even with a bad flex cable you can access 32k depending on what is bad in the flex cable card.  So I plugged in a disk controller and trying to catalog a drive I get:

 

I/O ERROR 06

 

I have verified the CRUCLK lines are good and no broken wires anywhere on the firehose cable.  I have also swapped the flex interface out with a original on my daily used system and it all works.  

 

I have also swapped out the 74LS245 on the PEB card.

 

Any suggestions where else to look?

 

 

Edited September 11, 2021 by Shift838

[+dhe]

   I remember the exact same case from 30 years ago, in that particular case, the fix was easy, someone had gotten gunk on a particular set of fingers on the expansion card - I should have wrote down which ones - a little work with a gum eraser and if was 'fixed'.

   So, it's kind of a pain, but if you have the schematic, you might check continuity from both the fingers and the expansion port side, to what ever chip/pin is their first stop.

[Madhatter1]

This may not apply to you.

I had a problem back in the 80s

I took my system to the TI service center they found the problem was with the flex card and wanted to charge me quite a bit to replace it.

Knowing there was not that much to the flex card, I took it home and checked myself and found during Mfgring they had a solder bridge that was causing my problem.

It's been so long a ago I don't remember where it was.

[Shift838]

So I went through and tested all the connections between the 99/4A bus and the flex cable connector and then the flex cable connector to the ICs as well as everything on the PEB BUS.

 

All tested just fine.  The card did look like either someone replaced the LS244's or someone did not know how solder that well on a few pins of the 244's.  Not all the pins, just a few or they had too much to drink.

 

Re-heated those solder points and nada... still the same issue.  pulled out my USB microscope and starting checking for anything that would glare out at me..

 

started looking at each IC and not something I could even see with my nice super magnification solder specs but the microscope picked it up.  One of the LS244's pin #3 was (1/2 of the pin) was actually bent under the chip.  And whoever put it on the board instead of taking it off and straightening the pin out just put a glob of solder down to make it look like the pin was soldered.

 

removed the chip and decided to remove them all and socket them.  plugged all the IC's back in and now another dead flex card has been brought back to life.

 

 

 

[+Ksarul]

Good sleuthing. Hidden pins like that can be a real pain.

[XLERB]

I know this is a months-old topic, but I had a similar experience. Got a PEB off eBay that had apparently been sitting in storage unopened since it came from the factory, and when I plugged it in and put all my cards in, they lit up and the disk drive spun, but the 32K memory wasn't found and I always got a "device error" code on the disk drives. Even my speech synthesizer on the Triple Tech card wasn't working. I dutifully cleaned and re-seated all the connectors, but nothing changed.

 

I swapped in my old "firehose" cable card, and everything worked fine. It'd be interesting to look closely and see if there was any sloppy soldering or bent pins on the replacement cable connector or card. Back in the day when I bought my original PEB, TI was still exchanging them under warranty even though they'd stopped selling them, and I never heard about any complaints at the time. But it sure seems there might have been some poor quality control on the flexcable interfaces. Of course, it's possible that something dried out or failed while it sat in storage for 35 years or when I unrolled it, but I suspect the problem might have been there from the factory, since my old one sat rolled up in the basement for almost that same length of time...