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HP 54540A scope, any hope of repair ?

G

George Pontis

Jan 1, 1970
0
Hi Group,

I've got a 54540A in need of repair. This is a 4
channel 500 MHz digitizing scope of the generation
before Infinium. When first turned on it appears that
nothing happens. But it is alive to the degree that it
recognizes if you hold down a key during power-up,
which is the signal to prompt for a firmware update.
In this case a prompt appears on the CRT, and you need
to confirm with another keypress if you really want to
read in new firmware. If I press another key (even
though I don't have a new disk for it), then it
appears to go dead again.

I have checked all the power supply voltages and found
everything in order. My theory is that some part is
failing the power up self test early in the sequence,
and it is not able to display an error message at that
time. HP service consisted of exchanging keyboard or
main board assemblies, which would be determined by
swapping in a known good one. A replacement assembly
would probably be too expensive even if they had one
available.

Before I write this off ... does anyone know how to
access any further diagnostc info, or if there are any
specific things that I could check and possibly repair
to fix this ?

Geo.
 
George said:
Hi Group,

I've got a 54540A in need of repair. This is a 4
channel 500 MHz digitizing scope of the generation
before Infinium. When first turned on it appears that
nothing happens. But it is alive to the degree that it
recognizes if you hold down a key during power-up,
which is the signal to prompt for a firmware update.
In this case a prompt appears on the CRT, and you need
to confirm with another keypress if you really want to
read in new firmware. If I press another key (even
though I don't have a new disk for it), then it
appears to go dead again.

I have a 54542A with exactly the same problem. I first noticed it
after a nearby thunderstorm, although it had been plugged in but
switched off at the front panel, so that may be coincidence. It
happened a few months ago. Could it be a date related boot code bug?
If so, maybe resetting the calendar chip (by disconnecting the battery)
might help? Maybe the lithium battery has discharged and it can't run
without it? Maybe there is a corrupt flash/eprom memory?

I do have a couple of firmware floppies, v1.30 and 1.50 (16 March 94).
More recent firmware exists (with improvements to the FFT code and
perhaps more), but I have been unable to obtain it so far.

If I do a button-pressed power up, I get to the point where it asks for
the shift key to be pressed to reload firmware. When I press it with a
floppy inserted, there is no sign that the scope attempts to read the
floppy. The floppy led does not light up, nor is there any sound of
head seeking.

I would really like to get this working again. I looked at the
diagnostic flowchart in the service manual, but this situation is
simply not covered. I haven't opened it up yet to check the psu
voltages, but that is the obvious next step. I somehow suspect that
they will be fine - but maybe the lithium battery will be interesting
to measure.

It would be nice to get a copy of the schematics.


John Walliker
 
G

George Pontis

Jan 1, 1970
0
I have a 54542A with exactly the same problem. I first noticed it
after a nearby thunderstorm, although it had been plugged in but
switched off at the front panel, so that may be coincidence. It
happened a few months ago. Could it be a date related boot code bug?
If so, maybe resetting the calendar chip (by disconnecting the
battery) might help? Maybe the lithium battery has discharged and it
can't run without it? Maybe there is a corrupt flash/eprom memory?

I do have a couple of firmware floppies, v1.30 and 1.50 (16 March 94).
More recent firmware exists (with improvements to the FFT code and
perhaps more), but I have been unable to obtain it so far.

If I do a button-pressed power up, I get to the point where it asks
for the shift key to be pressed to reload firmware. When I press it
with a floppy inserted, there is no sign that the scope attempts to
read the floppy. The floppy led does not light up, nor is there any
sound of head seeking.

I would really like to get this working again. I looked at the
diagnostic flowchart in the service manual, but this situation is
simply not covered. I haven't opened it up yet to check the psu
voltages, but that is the obvious next step. I somehow suspect that
they will be fine - but maybe the lithium battery will be interesting
to measure.

It would be nice to get a copy of the schematics.


John Walliker



With some effort I was able to get to the lithium cell, and found that
it had dropped to 200mV instead of the 3V nominal value. I shorted it
out momentarily, then connected a couple of alkaline AA in parallel
with it. The scope powered up right away!

The downside is that all calibration info has been lost. The scope is
visibly in error with the default values loaded. Oh well, it should be
easy enough to calibrate since most of the volatile parameters seem to
be DC effects.

FYI, the battery is marked "Sanyo CR17450SE". It is an A size cell with
radial leads, 3V / 2500mAH.

--
 
E

Erik Baigar

Jan 1, 1970
0
George said:
The downside is that all calibration info has been lost. The scope is
visibly in error with the default values loaded. Oh well, it should be
easy enough to calibrate since most of the volatile parameters seem to
be DC effects.

Did you try the calibration from the

Utility -> Self cal menu

Maybe this leads to better DC results...
I suppose you get as current configuration
a "D" for defaulted, right?

Regards,

Erik.
 
E

Erik Baigar

Jan 1, 1970
0
I do have a couple of firmware floppies, v1.30 and 1.50 (16 March 94).
More recent firmware exists (with improvements to the FFT code and
perhaps more), but I have been unable to obtain it so far.
My HP54542a currently runs a 2.30 from July 95. But
unforuntately I do not have the firmware disks. I'd
be highly interested in getting one, too...
I would really like to get this working again. I looked at the
Yes, this is a very nice oscilloscope and I'd be
interested whether replacing the battery helps
in your case, too. Of course shorting the power
supply for a few seconds is a good idea to erase
all contents of the RAM!
It would be nice to get a copy of the schematics.
Yes, this would be great. There are some parts
inside which are not replaceable (apart from the
samping circuits) like the FPGA. I have got
empty ones but I do not have got a programmer
to copy the EPM5128 of the HP54542a...

John, please keep us up to date,

regards

Erik.
 
Erik said:
John, please keep us up to date,

I certainly will. I have some samples of a very similar lithium cell
- the CR17450E-R - built into a battery pack which I could break up.
These are the laser sealed version with a glass-to-metal feedthrough,
intended for high temperature high reliability applications. I will
probably have a look at my 'scope next week. It might be interesting
to see whether it retains its calibration if I do a hot swap of the
battery.

John
 
I now have a fully working 'scope again.

I checked the power supply voltages and these were fine. The lithium
cell was fully discharged - the voltage was about 270mV. To reduce the
risk of damage to the main board I cut the connections to the old cell.
The new one had nickel strips welded onto the ends, so I soldered
these onto the stubs from the old cell. (Never solder directly to the
body of a Li cell.)

On powering up with the replacement cell, the 'scope displayed a
message warning of a calibration memory checksum error and
recommending firmware recalibration.

There was a minor problem when I recalibrated - the channel 1 adc
calibration failed, so I swapped the cables to channels 1 & 2 (thinking
that I might have a defective cable) and restarted the calibration from
the beginning. This time everything was fine and all calibrations
passed.

The repair did take some time, as the floppy drive, power supply,
back panel, various cables and finally the main board have to be
removed to gain access to the Li cell. The hardest part was loosening
the input BNC connector nuts from the front panel without damaging
them. This is because the nuts are domed and have very little flat
area to grip with a spanner.

All the information needed to dismantle the 'scope and to recalibrate
it is in the service manual. It is a pity that the discharge of the Li
cell (which is a predictable and inevitable event) is not documented
anywhere or reported in a diagnostic message, especially as the
symptoms could easily lead to the assumption that there is a
serious fault.

John
 
E

Erik Baigar

Jan 1, 1970
0
I now have a fully working 'scope again.

Hey, that is really good Congratulations! It
is salving to know, that lost RAM contents do not
render the instrument useless...

Enjoy ths scope,

regards,

Erik!
 
Enjoy ths scope,

I certainly will. I have been using it since it was new. It was
originally chosen in competition with LeCroy and Tektronix.
The reason it won the competition was that it was the only
one which could capture 1ns glitches at slow timebase
speeds. Even now, many digital 'scopes will miss narrow
glitches when the timebase is set to something like
100ms/division. The disadvantage is that the display is not
updated until a whole sweep has been captured. This does
not suit everyone, but I have found it to be a worthwhile
tradeoff because I can see things that other much newer
'scopes miss. I also have a set of 800MHz FET probes.
These make a big difference compared with passive
probes - the positioning of the ground connection makes
MUCH less difference to the captured waveform.

John
 
E

Erik Baigar

Jan 1, 1970
0
The reason it won the competition was that it was the only
one which could capture 1ns glitches at slow timebase
speeds. Even now, many digital 'scopes will miss narrow
glitches when the timebase is set to something like
100ms/division.
Yes, that is indeed a problem. Additionally many newer
scopes show a pretty nice sinus of 10kHz while the
real input signal is 100.01MHz ;-)
The disadvantage is that the display is not
updated until a whole sweep has been captured. This does
not suit everyone, but I have found it to be a worthwhile
tradeoff because I can see things that other much newer
'scopes miss.
Other advantages for me are:
- It has allfeatures already built in: In many Tek
instruments you have to pay for a memory stick
enabling FFT.
- The possibility adjust the time-offset between
channels is very nice in monitoring and comparing
fast signals on different channels with cables of
different length.
- Setups are recalled very fast. I was often vexed
about a TEK TDS620 at work: Recalling a setup you
could nearly follow how a macro "pressed" the required
buttons virtually...
- Trigger offers some nice features in capturing
digital signals on more channels.
- Nice mathematical functions like integration
built in - i.e. the oscilloscope can directly
calculate charge or energy.
- Deep memory of 32k is of advantage and the
possibility to acquire e.g. 50 trigger events
which each using 512 points is often helpful!
- I do not like autoscale - but I some one uses
it and unacceptable settings result, there is an
UNDO button ;-)
- No harddrive with windows inside - i.e. one does
not have to reboot because windows crashed ;-)
I also have a set of 800MHz FET probes.
These make a big difference compared with passive
probes - the positioning of the ground connection makes
MUCH less difference to the captured waveform.
Yes, that is excellent, too. Mine came with 1145A
which I enjoy as well..

Best regards,

Erik.
 
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