The problem is some programmers will not blow them
unless the chip is in the unblown state and there is no way to return these
chips to the erased state.
?
How do you create a programming file for these
chips? If they have a security fuse they cannot be read.
?
I avoid messing with this stuff anymore. I prefer
to work with analog instruments wit no micros now.
?
Bob Macklin
K5MYJ
Seattle, Wa.
"Real
Radios Glow In The Dark"
?
?
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----- Original Message -----
Sent: Wednesday, February 17, 2016 10:47
AM
Subject: Re: [hp_agilent_equipment] HP
8753B CPU issue
?
On Wed, 17 Feb 2016, Bob Macklin macklinbob@... [hp_agilent_equipment]
wrote:
Luckily enough that failure usually caused by blown fuses
self-healing so
they are no longer blown. It can be cured by re-programming
them with the
same valid pattern so the ressurrected fuses would get blown
again. It does
NOT guarantee the failure won't happen again but allows
fixing those
instruments without programming new virgin chips. Programmed
new chips will
have that exactly bit rot problem and they are rare as hens'
teeth -- try to
find e.g. PLS155 in PLCC package...
>
Bipolar/Fuseable Link PALs have the same Bit Rot problem of ROMs of that
period.
>
> Bob Macklin
> K5MYJ
> Seattle, Wa.
>
"Real Radios Glow In The Dark"
> ----- Original Message -----
>
From: Nathan Johnson jdownj@... [hp_agilent_equipment]
> To:
ChuckA chuck@... [hp_agilent_equipment]
> Sent: Wednesday,
February 17, 2016 8:31 AM
> Subject: Re: [hp_agilent_equipment] HP 8753B
CPU issue
>
>
>
>
> I'm sure you already
considered, but the PAL was burned fresh, or swapped from a board of the same
revision? As a programmable device, it is possible that the code in the PAL
did change between board or prom revisions.
>
>
> Note that
I have no knowledge of that unit specifically but I just got burned by
different PAL code on a different repair.
>
>
>
Nathan
> KK4REY
>
>
> Sent using CloudMagic
Email
>
>
> On Wed, Feb 17, 2016 at 19:09, ChuckA
chuck@... [hp_agilent_equipment]
>
>
>
I've been working on this problem 8753B CPU card for a few months now
>
with very limited results. The original problem was no video, which I
>
tracked down to a bad PAL 16R1 chip, replacing that got me a screen
with
> random lines and various flashing characters. I thought that
problem was
> bad DRAM so I replaced them, still no change. Watching the
status lights
> while changing the position of the A9CC jumper and
pressing the "PRESET"
> button I was able to get it to occasionally
start to work, but not all
> the time.
>
> The short story
is I can now get it to run every time by following
> this procedure;
turn the unit on with the A9CC jumper in the "NORMAL"
> position, then
move the jumper to the center position and press
> "PRESET", then move
the jumper to the next position to the right and
> press "PRESET". This
will display "DRAM Passed" on the screen, then move
> the jumper back to
the "NORMAL" position and press "PRESET", at which
> time the unit will
start up and operate normally as long as power is
>
applied.
>
> Any change in that sequence and it will not operate.
I've swapped the
> PROM's into a working board and they work
fine.
>
> Anyone have any idea what is going on with
this?
>
> Chuck
>
> --
> See Early TV
at:
>
>
www.myvintagetv.com
>
>
>
>
>
>
---
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