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| HP8595E spectrum Analyzer: readings at -40dB and CAL SIGNAL NOT FOUND |
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| auato:
Hi, After a long disuse period I turn it on and after a while it turns off definetively. Once the PSU has been fixed, it runs again but measures almost 40dB less. If I try to calibrate it or try the CONF TEST, it returns "CAL signal not found". -checked the voltages (all LEDs on PSU are on) and I have TP403=+5.14V, TP404=+12.10V, TP401=+14.94V, TP402=-15.00V but I am not able to find where I can check +24Vdc (it looks that 8590A service manual doesn't mention any 24Vdc rail); -checked the output calibration signal with another SA and it is OK (300MHz @-20dBm); -the backup battery still seems to be good (3.01V); -at the top left, the year has two question marks (attached video); -in the attached photo I don't remember whether the connector with a purple thin wire starting from the PSU is connected somewhere ; -if CAL AMPTD runs after entering the deep debug mode (Frequency --> -37Hz) the calibration starts but when it is into the EMI-test part it goes into a loop and no longer exits until I abort the procedure. But what happened to it? https://youtu.be/CKte98jvFmI?si=KDvNotXRYJM_psud edited: I would like to measure +24Vdc |
| MarkL:
I would try to characterize the problem a little more. The first thing I would try is different attenuator settings. You might have a bad step in your attenuator. Do you have a signal generator to test the high band (2.9GHz - 6.5GHz)? Could be a problem with just the low band. You could try defaulting the calibration constants using the procedure in the Assembly Service Guide. See "If the analyzer displays a low signal level" on page 234. On the date/time issue, can you set the date to a sane value, and after unplugging the analyzer for a minute then plugging it back in, does it it keep time? How long was your "long disuse period"? I'm not sure if the goofy year could point to possible NVRAM corruption, but it's something to keep in mind. I'm not seeing a +24V supply on the schematic. Is there one? According to the Assembly Service Guide, the purple wire supplies -24V to the A7 analog control board on 8592L and 8593E analyzers. (I believe it's used to extend the YIG tuning range for those models.) On the 8595E, it doesn't go anywhere and just terminates in a 3-pin housing that's left hanging. |
| DavidAlfa:
You definitely should have 24V, or the switches won't work, just check how the attenuator clearly says 24V, if missing it would explain it all. Once you have the 24V tested working, if the signal keeps failing: The attenuator block has four elements (-5, -10, -20, -40dB) and makes a combination of them in series and/or bypassed. If one of them is burned, you'll get an open circuit. So try finding a signal by manually setting attenuation to -5, -10, -20 and -40dB. It's pretty easy to disassemble, but there're a lot of screws behind the cover, where the sma connectors are. This is it: One 8592 had that one burned, other had a burned transistor array which activated a rf switch, whose coil was completely roasted, can't remember what it was for. It was a latching switch, so it only needed a small pulse to change, but the switch contact had fallen (Plastic rivets...), so my guessing is the system did not detect it switching and kept energyzing the coil until it overheated, then everything burned down in a chain. |
| MarkL:
--- Quote from: DavidAlfa on December 10, 2023, 12:06:44 am ---You definitely should have 24V, or the switches won't work, just check how the attenuator clearly says 24V, if missing it would explain it all. ... --- End quote --- The label doesn't mean there's a 24V supply. The attenuator is supplied with +/-15V on J5 pins 3 and 10. See schematic snippet below. But the point remains it could still be a bad attenuator step. I think we both agree on that. |
| DavidAlfa:
The label means the coils in the attenuator are meant for 24V, thus the logic tells it'll be powered at that voltage. These are also available in 5 and 15V versions IIRC. Or maybe someone replaced the attenuator block with a wrong one? There're also 5 and 15V versions, so it's strange HP mounted a 24V part there. Wether HP used them like this, I don't know. |
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