3 Apr
2009
3 Apr
'09
4:20 p.m.
I have a 16K memoryboard for my HP9825A it suffered from a bad -12V and
destroyed all the rams TMS4080.
I bought from ICI 32 pcs. nos uPD411AC-2 replaced all the rams but I'm
getting an error when testing the board.
The HP9825 isn't under suspect because it works okay with another 16k board.
The systemtest (from the tape) says : 60K board failes
Address 60100,60300,60400 not always the same sometimes only 60400.
Bit 9 sense 0 or 1 (not consistent sometimes 1 sometimes 0) I swapped the
LB9 and UB9 chips on the board with other 411's(new ones)
But the error stays I replaced the refreshcounters decoupling caps but
nothing.
So any ideas are welcome.
-Rik
4 Apr
4 Apr
4:04 p.m.
I have a 16K memoryboard for my HP9825A it suffered from a bad -12V and
I assume you have schematics.
destroyed all the rams TMS4080.
This puzzles me a bit. The -12V rail is regulated down to -5V using a
resistor/zener circuit,. and it's the -5V that's used by the RAMs. I
assume you've checked this voltage.
Or did the -12 disappear, removning the bias from the DRAMs and cooking them?
I bought from ICI 32 pcs. nos uPD411AC-2 replaced all
the rams but I'm
getting an error when testing the board.
The HP9825 isn't under suspect because it works okay with another 16k board.
The systemtest (from the tape) says : 60K board failes
Address 60100,60300,60400 not always the same sometimes only 60400.
Bit 9 sense 0 or 1 (not consistent sometimes 1 sometimes 0) I swapped the
LB9 and UB9 chips on the board with other 411's(new ones)
But the error stays I replaced the refreshcounters decoupling caps but
nothing.
First check the power lines with a 'scope. Noise on power lines causes
all sorts of problems with DRAMs.
I've had vias fail on old HP boards when soldering/desoldering
components. My next task would be to check that all pins on all RAMs go
to the rignt places and that none are left floating.
And then do make sure that all address, data, etc pins are being driving
nad that none are floating around.
-tony
5 p.m.
-----Oorspronkelijk bericht-----
Van: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] Namens Tony Duell
Verzonden: zaterdag 4 april 2009 22:05
Aan: cctalk at classiccmp.org
Onderwerp: Re: HP 9825 16K 09825-66523 memoryboard failure
Yep, thanks to your excellent work.
I have a 16K memoryboard for my HP9825A it suffered from a bad -12V
and
I assume you have schematics. destroyed all the rams TMS4080.
This puzzles me a bit. The -12V rail is regulated down to -5V
using a resistor/zener circuit,. and it's the -5V that's used
by the RAMs. I assume you've checked this voltage.
Or did the -12 disappear, removning the bias from the DRAMs
and cooking them? I bought from ICI 32 pcs. nos uPD411AC-2 replaced
all the
rams but I'm
getting an error when testing the board.
The HP9825 isn't under suspect because it works okay with
another 16k board.
The systemtest (from the tape) says : 60K board
failes Address
60100,60300,60400 not always the same sometimes only 60400.
Bit 9 sense 0 or 1 (not consistent sometimes 1 sometimes 0)
I swapped
the
LB9 and UB9 chips on the board with other 411's(new ones) But the
error stays I replaced the refreshcounters decoupling caps but
nothing.
First check the power lines with a 'scope. Noise on power
lines causes all sorts of problems with DRAMs.
I've had vias fail on old HP boards when
soldering/desoldering components. My next task would be to
check that all pins on all RAMs go to the rignt places and
that none are left floating.
And then do make sure that all address, data, etc pins are
being driving nad that none are floating around.
-tony
Thanks,
-Rik
5:40 p.m.
----------------------------------------
From: hp-fix at xs4all.nl
That wasn't the problem, the errors are a bit erratic always the same bit 9
but not always the same address.
Today I replaced the address buffer ('LS368) but that wasn't the solution
too.
Hi
Do realize that with a RAM array, the failing location
of a RAM test is not always the bad RAM. It could be most any
of the other RAMs on that same wire.
Dwight
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5 Apr
5 Apr
6 a.m.
It's not really a array.
The banks are build op from 16 times 1*8k RAM's there are two banks one low
one high.
Octal 60 and 70 and I replaced on both banks the bit 9 chips, because the
program marked the bit 9 as faulty.
The problem is it's always bit 9 but not always the same address and not
always the same output sometimes sense is 0 sometimes sense is 1.
So the suggestion from Tony to check the vias, is the next step I'll take.
-Rik
-----Oorspronkelijk bericht-----
Van: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] Namens dwight elvey
Verzonden: zaterdag 4 april 2009 23:41
Aan: General Discussion: On-Topic and Off-Topic Posts
Onderwerp: RE: HP 9825 16K 09825-66523 memoryboard failure
----------------------------------------
Rediscover_Storage1_042009
From: hp-fix at xs4all.nl
That wasn't the problem, the errors are a bit erratic
always the same
bit 9 but not always the same address.
Today I replaced the address buffer ('LS368) but that wasn't the
solution too.
Hi
Do realize that with a RAM array, the failing location of a
RAM test is not always the bad RAM. It could be most any of
the other RAMs on that same wire.
Dwight
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12:57 p.m.
destroyed all the rams TMS4080.
This puzzles me a bit. The -12V rail is regulated down to -5V
using a resistor/zener circuit,. and it's the -5V that's used
by the RAMs. I assume you've checked this voltage.
Or did the -12 disappear, removning the bias from the DRAMs
and cooking them? That wasn't the problem, the errors are a bit
erratic always the same bit 9
but not always the same address.
Today I replaced the address buffer ('LS368) but that wasn't the solution
too.
I think you're going to have to do some measurements before reolacing odd
components at random. As I mentioned. some of these old HP boards don't
like being resoldered too often, the through-hole plating fails and leads
to more problems. Please don't ask how I discovered this!
I've had
vias fail on old HP boards when
soldering/desoldering components. My next task would be to
check that all pins on all RAMs go to the rignt places and
that none are left floating.
I'll think I'm going to do that I got a current tracer, so I'm going to use
that first.
6 Apr
6 Apr
5:07 p.m.
New subject: HP 9825 16K 09825-66523 memoryboard failure NOT ANY MORE !
To keep you posted :
I made a error by stating the -12V was wrong, it was the +12V that's why I
replaced the uA723. (mea culpa etc....)
The TMS4060's don't have a -12V connection they get +5,+12,0,-5V.
The board is working again, the VCC pin of lowerbit 9 had a resistance of
12.5 ohm to the VCC-line.
The A10 pin of the same chip didn't connect to anything.
A little bypassing did the job, so thanks for your advice.
-Rik
-----Oorspronkelijk bericht-----
Van: cctalk-bounces at classiccmp.org
[mailto:cctalk-bounces at classiccmp.org] Namens Tony Duell
Verzonden: zondag 5 april 2009 18:57
Aan: cctalk at classiccmp.org
Onderwerp: Re: HP 9825 16K 09825-66523 memoryboard failure
I thought hte -12V rail came from a 3-terminal regulator
(7912 or similar). There's a 723 in the _+12V_ supply IIRC though.
I'm going
> > destroyed all the rams TMS4080.
>
> This puzzles me a bit. The -12V rail is regulated down to
-5V using
> a resistor/zener circuit,. and it's the
-5V that's used
by the RAMs.
I assume
you've checked this voltage.
Or did the -12 disappear, removning the bias from the DRAMs and
cooking them?
The -12V was defective (not on this machine but on another witch I
fixed
(uA723 replaced) and put a 8k board in it.) That wasn't the problem, the errors are a bit
erratic
always the same
bit 9 but not always the same address.
Today I replaced the address buffer ('LS368) but that wasn't the
solution too.
I think you're going to have to do some measurements before
reolacing odd components at random. As I mentioned. some of
these old HP boards don't like being resoldered too often,
the through-hole plating fails and leads to more problems.
Please don't ask how I discovered this!
> I've had vias fail on old HP boards when
soldering/desoldering
> components. My next task would be to check that all pins
on all RAMs
go to the
rignt places and that none are left floating.
I'll think I'm going to do that I got a current tracer, so to use that first.
Using an ohmmeter on the board (with it powered down, of
course) will verify that all the address lines are connected
between the RAMs, etc.
-tony
7 Apr
7 Apr
3:56 p.m.
New subject: HP 9825 16K 09825-66523 memoryboard failure NOT ANY MORE !
To keep you posted :
I made a error by stating the -12V was wrong, it was the +12V that's why I
replaced the uA723. (mea culpa etc....)
OK, that makes a lot more sense.
The TMS4060's don't have a -12V connection
they get +5,+12,0,-5V.
Indeed. And that's why I was pussled. From what I rememebrm the memory
_board_ takes in -12V from the PSU (it comes from a 3-terminal regulator
there) and brings it down to -5V for the DRAMs using a zener and resistor.
The board is working again, the VCC pin of lowerbit 9
had a resistance of
12.5 ohm to the VCC-line.
Bad trace?
The A10 pin of the same chip didn't connect to
anything.
Ditto?
A little bypassing did the job, so thanks for your
advice.
Yes, I've seen it all too often on old HP boards. The through-hole
plating isn't that good. My HP9830 had a couple of bad connections on one
of the RAM boards (which is the main reason why the machine didn't work
when I got it). Adding acouple of jumpers fixed that. And I've seen it in
other machines.
-tony
6 Apr
6 Apr
5:17 p.m.
New subject: Repair: HP 9825 16K 09825-66523 memoryboard failure
I think Tony will agree with me, if not I'll hear about it. If you want to
save the board and don't care about the ( dead ) DIP ICs you are removing,
cut all the legs off of the DIPs and remove them one-by-one with minimal
heat and long-nosed pliers. Also don't use solder wick but rather poke a
round wooden toothpick in the hole to clean it out. This will cause the
least amount of damage to the board and I haven't lost a via yet with this
method. Good luck.
Best regards, Steven
----- Original Message -----
From: "Tony Duell" <ard at p850ug1.demon.co.uk>
To: <cctalk at classiccmp.org>
Sent: Saturday, April 04, 2009 1:04 PM
Subject: Re: HP 9825 16K 09825-66523 memoryboard failure
I've had vias fail on old HP boards when soldering/desoldering
components. My next task would be to check that all pins on all RAMs go
to the rignt places and that none are left floating.
And then do make sure that all address, data, etc pins are being driving
nad that none are floating around.
-tony
7 Apr
7 Apr
4:09 p.m.
New subject: Repair: HP 9825 16K 09825-66523 memoryboard failure
I think Tony will agree with me, if not I'll hear about it. If you want to
save the board and don't care about the ( dead ) DIP ICs you are removing,
You'll get no arguements from me there!.
cut all the legs off of the DIPs and remove them
one-by-one with minimal
heat and long-nosed pliers. Also don't use solder wick but rather poke a
round wooden toothpick in the hole to clean it out. This will cause the
Applying a soldering iron to one side to melt the solder and suching it
out with a solder sucker from the other side is also relatively 'kind' to
the PCB.
least amount of damage to the board and I haven't
lost a via yet with this
method. Good luck.
I susepct, alas, that some older HP boards may be damaged even my this
method. They really are fragile now.
-tony
5585
days inactive
5589
days old
9 comments
4 participants
participants (4)
-
ard＠p850ug1.demon.co.uk -
dkelvey＠hotmail.com -
hp-fix＠xs4all.nl -
steven.alan.canning＠verizon.net