turbogtu

I'm looking for someone who has successfully accomplished this feat. The ones that I do work for a matter of minutes then die again or go crazy. Looking for any advice on the correct way to accomplish this.

jimmyblue

iTrader: (11)

I've done a lot of soldering and a little programming,
though never in a PCM.

If you are eating EPROMs, consider checking out the
supply voltage - level and noise - to be sure it's not
the environment that's killing them. This wants a
'scope (for noise anyway).

A marginal programming can also be flaky or fade and
go to wrong bits. I've used a Willem programmer on
27C128 type EPROMs with some success but there are
other types where the settings have to be massaged
really carefully, or just don't work at all. Check your
programmer's VPP voltage during programming against
what the manufacturer requires.

turbogtu

I'm using a willem and have attempted different voltages with different sources...all results the same. The programming part works almost flawlessly...its once I fire them up that weird things happen. Mostly that it works absolutely fine, but only for a couple minutes then dies. However, if I let it sit it will repeat its performance of functioning for a small time. Odd. Your talk of bits fading makes sense, but then why will it come back? Also I have desoldered some after failure and verified the memory against the source and it comes back OK.

jimmyblue

iTrader: (11)

I wonder if you need a higher speed-grade EPROM.
My use was a hand-built pattern generator for the
baseband signal of a RF modulator. I found my 45nS
UV EPROMS woiuld work fine, but my 70nS OTP ones
would either not work at all, or begin to put out bad
pattern once they got warm (hot=slow for CMOS).

Maybe get a can of freeze spray and test that theory?

turbogtu

That makes the most sense, I'll see if I can test that one out. If I could find some new chips to buy I would try that also, but I haven't had any jump out at me and my search has been half-assed.

turbogtu

Ok, so the original chip is a AB28F400B5.... by intel. The I can get ahold of easily now is a PA28F400B5. I have had no luck tracking down datasheets. I do however have one for the original chip. I am willing to bet the lead configuration is the same on this chip as the original. However it is a different chip and is a 4mb chip. can I use this one in place of the original? Will I need to do anything fancy to compensate for the size difference (offset anything) - an erase should set the thing to 0s, so only written part will be the 512k I put on it right?

jimmyblue

iTrader: (11)

These are EEPROM devices I gather, why are you not
in-situ programming them? Is there something special
going on here that makes you take them out of the
PCM?

A larger memory might need you to tie down unused
address pins. But with the root part number being the
same I would not expect them to be different in size.

turbogtu

Trying to fix pcms that have been deemed brain dead by programs such as EFI Live and HP tuners