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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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HP 54540A scope, any hope of repair ?
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. |
#2
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HP 54540A scope, any hope of repair ? I have the same problem!
George Pontis wrote:
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 |
#3
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HP 54540A scope, any hope of repair ? I have the same problem!
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#4
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HP 54540A scope, any hope of repair ? I have the same problem!
George Pontis wrote:
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. |
#5
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HP 54540A scope, any hope of repair ? I have the same problem!
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#6
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HP 54540A scope, any hope of repair ? I have the same problem!
Erik Baigar wrote:
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 |
#7
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HP54542A lithium battery was discharged making oscilloscope appear faulty
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 |
#8
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HP54542A lithium battery was discharged making oscilloscope appearfaulty
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#9
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HP54542A lithium battery was discharged making oscilloscope appear faulty
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 |
#10
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HP54542A lithium battery was discharged making oscilloscope appearfaulty
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