[Techtoolslist] 29B EPROM Programming Woes...

Fri Mar 30 11:07:40 EDT 2018

Okay, just a little followup on this for the archives...

I took this moment to do several things with my 29B and I have some improvements as a result....

What I did:

  1.  Replaced all the mainboard Tantalum Caps - these can be identified as they are 'blob' looking and are tannish yellow. I had to replace about 9 of them around the Power Supply and these ranged from 2.2uf to 220uf. Luckily since I re-cap monitors all the time, I had lots of equivalent 105 degree electrolytic caps in my parts to match these.
  2.  I guessed that the tiny square tannish-yellow 5v bypass capacitors on my mainboard were not Tantalum as they were very small and also pretty high voltage, I didn't think they could possibly be tantalum due to those properties. I might be wrong, but I left them alone (there were also like 10 of them)
  3.  I went through the Power Supply calibration measurements, it was challenging without an extender card/cable but I was still able to get my DMM probes in there to the test points. Everything in there was pretty good so I did not need to adjust anything.
  4.  I also took the time while I was in there to upgrade my 256K Expansion Memory board to 1M... I had a set of RAM and sockets that I had ordered years ago, and took the time to do it now
     *   It was tedious and meticulous. The traces are super small but I wouldn't call them fragile by any means but if you aren't pretty good with a soldering iron, I can see how this could become disastrous.
     *   Once you have everything out, inspect your PCB for damage you might have caused and clean it up with Flux cleaner etc... I used a magnifying glass because apparently now Im old and can't see small things anymore, Im not entirely sure when this happened.
     *   The bypass capacitors that need to be moved... they really need to be moved!! I assumed that I could just leave them and throw in some other bypass caps in the new locations..  After booting I was getting a 'Parity Error #62'. However these are not normal bypass caps... they are actually 33uf for being so small. I had to remove all the ones I put in in the new locations and moved the old ones over, just like the instructions said (docs are on the TTL FTP site for this). Then no more parity errors... Whew... Instructions to the rescue!
     *   Select B -2 - Start reported a solid 1M memory after this.

After all this, I again started programming a set of EPROM's, both 27128 varieties and 27256 varieties by different manufacturers from my 'old EPROM' bin. I was able to program the SEEQ, ST and TI EPROM's pretty decently, and the ones that failed were all the same old ones that had failed before, so Im concluding that those specific EPROM's might have issues (potentially related to the other programmer I was using)... Im going to stick to the 29B now since it actually has way better and 'specific' support for these part numbers and see how it goes.

Conclusions:

  1.  The capacitor upgrades needed to happen anyway because eventually the tantalum caps will have silver migration issues and start to create a DC load. Even tho my unit was built in 1985 and had all the newest designs, Im sure the caps were less than optimal after 30+ years of environmental stress.
  2.  I think I was in a 'statistical saddle' on my luck with the old EPROM's... I sorta put my mindset into 10% failure rate might be normal on using old devices.
  3.  Man TI27CXXX EPROMs program fast (TMS27C256 in 2 seconds) compared to others (sometimes 2+ minutes, the SEEQ's especially), they must have really spent some time getting their programming algorithm tweaked for them. NICE JOB TI!

Thanks to everyone for the tips, they were helpful to get my mind in the right place for all of this!!

Jess

-----Original Message-----

Heya Folks...

I have had a need to program a bunch of EPROMs lately (27128 varieties) and Im not sure if there are sunspots or something, but I can't seem to program anything on either my 29B OR my Intronics USB Programmer... I have successfully programmed like 4 EPROMs out of like 40 attempts. My EPROM's are old pulls from either Atari boards or other used ones I have acquired over the years in storage sticks.

They are either

ST 27128A

Fujitsu 27128

SEEQ 27128

TI TMS27C128

Im being fairly careful about the programming voltages and the 29B identifies the IC before programming it.

On the 29B I just get an Error #22 Programming Error right away.

Sorta the same thing on my Intronics.... Set it up, verify blank, program, error right away.

Are these just too old? Anyone have any good tricks?  The strange part is that I was having this exact same issue last night, then all of a sudden my 29B programmed 3 in a row just fine... today, nothing.

Thanks

Jess

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