Good afternoon all,
I have no real hope of anyone being able to help me but this is my last hope.
I have an HP 16500 logic analyzer. It will start and run for anywhere from a couple of seconds up to say a minute, to the point where it will have completed its boot process and is waiting to be used normally.
However, at that point it will shut down and attempt to come back up, fail, and then try again. It is clear that the power supply is the thing that is shutting down and then once it has shut down is trying to come back up, over and over again.
The system architecture is typical 90s--
There is a backplane into which are plugged:
1) The CPU card
2) The power supply card
3) The various logic analyzer cards—I have four: two 1 GSPS cards, and two 100MSPS cards
4) Power to two fans
5) A front panel interface connector (ribbon cable/IDE connector)
The video monitor assembly appears to be a separate assembly that was manufactured by Sony. There are a couple of cables that leave the video monitor assembly. One cable goes to the front panel and the other to a five pin connector on the power supply card. I assume that the second one is power to the assembly.
Okay, that’s the setup. I have done the following:
1) I removed the four logic analyzer cards
2) I disconnected the power to the two fans
3) I disconnected the front panel interface ribbon connector
4) I disconnected the various video monitor cables
With the four items above removed/disconnected the unit still tries and fails repeatedly to start.
I removed the CPU assembly from the backplane. After I did that the power supply refused to run at all. I therefore assume there is some kind of “CPU Installed” signal that the power supply needs in order to run. After I reinstalled the CPU the power supply “hunting” continued as before.
The unit has worked until recently and as I said at the beginning does come up and run for a short time, sometimes for as long as a couple of minutes before falling back into the "start-stop-repeat" sequence.
The Power supply card:
1) The power supply card runs on 115vac (the cord actually plugs into the back of it) and there is an LED on the board that indicates that 115vac is present when the power switch is ON.
2) There is an LED on the board that indicates when 120vDC (yes, DC) is present. There don’t seem to be any bleeder resistors across the large capacitors in the power supply so even after the power is turned off and the power cable disconnected both of those LEDs are illuminated for some time and to some degree, indicating the presence of charge on the capacitors. In fact the HP 16500 service manual points out explicitly that the service person is to wait at least six minutes for the charge to bleed away.
3) The service manual has a table of voltages that should be present on the power supply backplane connector. During the time that the unit is running properly the voltages are present. However, when the power supply is “hunting” the voltages rise and fall as you might expect.
I mentioned the possible lack of bleeder resistors above in order to make the point that in my experience here the chance of the unit starting properly (and actually running for a couple of minutes) increases dramatically the longer the unit is off between my attempts to get the unit to turn on. So maybe there is a voltage monitor circuit somewhere that is supposed to hold off startup until one of the voltages reaches some level--and maybe it’s out of whack, I don’t know.
I think this would be pretty easy to troubleshoot if I had the power supply and/or CPU board schematics. However, HP/Agilent no longer sell or support this unit and the service manual has no schematics or wiring diagrams.
I’m interested in any suggestions. And of course I am hugely interested in getting a schematic of the CPU and/or the power supply card.
Thanks in advance,
Ray Russell
Houston, TX
A bit of irrelevant history: Back in the 90s I bought a 16500B for the company for which I worked as a design engineer on DOD programs. It was an incredibly useful piece of equipment for debugging designs. If I recall correctly they were running about $20k at the time. Functional units today seem to be readily available on eBay for under $150 with shipping. I would say that is the deal of the century if you can find one that works—and that seems to be pretty easy to do. Who knows, I may just say to hell with this one and buy another one. That just offends my sense of DIY--ness.
I have no real hope of anyone being able to help me but this is my last hope.
I have an HP 16500 logic analyzer. It will start and run for anywhere from a couple of seconds up to say a minute, to the point where it will have completed its boot process and is waiting to be used normally.
However, at that point it will shut down and attempt to come back up, fail, and then try again. It is clear that the power supply is the thing that is shutting down and then once it has shut down is trying to come back up, over and over again.
The system architecture is typical 90s--
There is a backplane into which are plugged:
1) The CPU card
2) The power supply card
3) The various logic analyzer cards—I have four: two 1 GSPS cards, and two 100MSPS cards
4) Power to two fans
5) A front panel interface connector (ribbon cable/IDE connector)
The video monitor assembly appears to be a separate assembly that was manufactured by Sony. There are a couple of cables that leave the video monitor assembly. One cable goes to the front panel and the other to a five pin connector on the power supply card. I assume that the second one is power to the assembly.
Okay, that’s the setup. I have done the following:
1) I removed the four logic analyzer cards
2) I disconnected the power to the two fans
3) I disconnected the front panel interface ribbon connector
4) I disconnected the various video monitor cables
With the four items above removed/disconnected the unit still tries and fails repeatedly to start.
I removed the CPU assembly from the backplane. After I did that the power supply refused to run at all. I therefore assume there is some kind of “CPU Installed” signal that the power supply needs in order to run. After I reinstalled the CPU the power supply “hunting” continued as before.
The unit has worked until recently and as I said at the beginning does come up and run for a short time, sometimes for as long as a couple of minutes before falling back into the "start-stop-repeat" sequence.
The Power supply card:
1) The power supply card runs on 115vac (the cord actually plugs into the back of it) and there is an LED on the board that indicates that 115vac is present when the power switch is ON.
2) There is an LED on the board that indicates when 120vDC (yes, DC) is present. There don’t seem to be any bleeder resistors across the large capacitors in the power supply so even after the power is turned off and the power cable disconnected both of those LEDs are illuminated for some time and to some degree, indicating the presence of charge on the capacitors. In fact the HP 16500 service manual points out explicitly that the service person is to wait at least six minutes for the charge to bleed away.
3) The service manual has a table of voltages that should be present on the power supply backplane connector. During the time that the unit is running properly the voltages are present. However, when the power supply is “hunting” the voltages rise and fall as you might expect.
I mentioned the possible lack of bleeder resistors above in order to make the point that in my experience here the chance of the unit starting properly (and actually running for a couple of minutes) increases dramatically the longer the unit is off between my attempts to get the unit to turn on. So maybe there is a voltage monitor circuit somewhere that is supposed to hold off startup until one of the voltages reaches some level--and maybe it’s out of whack, I don’t know.
I think this would be pretty easy to troubleshoot if I had the power supply and/or CPU board schematics. However, HP/Agilent no longer sell or support this unit and the service manual has no schematics or wiring diagrams.
I’m interested in any suggestions. And of course I am hugely interested in getting a schematic of the CPU and/or the power supply card.
Thanks in advance,
Ray Russell
Houston, TX
A bit of irrelevant history: Back in the 90s I bought a 16500B for the company for which I worked as a design engineer on DOD programs. It was an incredibly useful piece of equipment for debugging designs. If I recall correctly they were running about $20k at the time. Functional units today seem to be readily available on eBay for under $150 with shipping. I would say that is the deal of the century if you can find one that works—and that seems to be pretty easy to do. Who knows, I may just say to hell with this one and buy another one. That just offends my sense of DIY--ness.