HP 54540A scope, any hope of repair ?

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.

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.

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...

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!

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.

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

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

Enjoy ths scope,

regards,

Erik!

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

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 ;-)

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 ;-)

Yes, that is excellent, too. Mine came with 1145A which I enjoy as well..

Best regards,

Erik.