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| HP3577A 5Hz-200Mhz VNA Teardown |
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| precaud:
I think it would be better to measure the temperature on one of the pcb's in the card nest that runs warm. That's where the effects of fan pressure changes would be greatest, and most consequential. Exposed power components near the fan aren't going to be affected much by it. |
| sixtimesseven:
--- Quote from: sixtimesseven on July 28, 2018, 06:37:09 pm --- --- Quote ---50dBa ! That's one noisey fan! The fan noise and crt are what keeps the 3577A (and 3562A) off my bench. Lovely instruments crippled with noisey fans and hard-to-read crts. --- End quote --- I probably just install a quiet 12V PC fan with a 24V converter and test with the thermal cam if the 80 CFM are enough without the CRT heating the instrument. --- Quote ---The Achilles heel of the 3577A appears to center around the input relays. That was the major design change between A and B versions, a redesigned front end using different relays. --- End quote --- Do you already have some with that issue? I'm still waiting on Artek to get me the service manual so I have no idea yet what these relays are, but are they replacable at all? --- End quote --- Teledyne 412 series apear to be still available at mouser: https://www.mouser.ch/Teledyne-Relays/Electromechanical/Relays/High-Frequency-RF-Relays/412-Series/_/N-5g33?P=1yzsh13Z1z0zl30 Rather expensive if you have to replace all of them! :o IDK, but maybe you can find the HP part number for the relay 0490-1404 in the service manuals of other instruments? |
| precaud:
--- Quote from: sixtimesseven on August 07, 2018, 03:57:52 pm ---IDK, but maybe you can find the HP part number for the relay 0490-1404 in the service manuals of other instruments? --- End quote --- Yeah, these things are pricey, that alone would have been good reason for HP to move away from them. I've found a couple other HP instruments from that era that use the same type relay, but not the exact same model. I found a couple 432-series in a DSO (forgot to write down the model number). And the 16531A digitizer plugin for 16500A logic analyzers has a couple of 'em, but I haven't pulled them yet to see their model number. Should be able to pick up those boards for cheap, noone is using them anymore. EDIT : The 432-series relays came from an HP 54200A, a 50MHz, 200Msa/S 6-bit DSO. The main board has three of 'em. |
| sixtimesseven:
--- Quote from: precaud on August 08, 2018, 02:38:00 am --- --- Quote from: sixtimesseven on August 07, 2018, 03:57:52 pm ---IDK, but maybe you can find the HP part number for the relay 0490-1404 in the service manuals of other instruments? --- End quote --- Yeah, these things are pricey, that alone would have been good reason for HP to move away from them. I've found a couple other HP instruments from that era that use the same type relay, but not the exact same model. I found a couple 432-series in a DSO (forgot to write down the model number). And the 16531A digitizer plugin for 16500A logic analyzers has a couple of 'em, but I haven't pulled them yet to see their model number. Should be able to pick up those boards for cheap, noone is using them anymore. EDIT : The 432-series relays came from an HP 54200A, a 50MHz, 200Msa/S 6-bit DSO. The main board has three of 'em. --- End quote --- Does using "old" relays make much sense though? I mean they could be at or near their end of life and it would be a shame to go trough the hole adjustment routine just to switch out relays again... |
| precaud:
--- Quote from: sixtimesseven on August 08, 2018, 06:37:42 pm ---Does using "old" relays make much sense though? --- End quote --- I don't have a problem with it. --- Quote --- I mean they could be at or near their end of life and it would be a shame to go trough the hole adjustment routine just to switch out relays again... --- End quote --- They could be, but probably are not (near their end of life). They've had a very easy life - the 54200A (and 54201x) 's I have here have been sitting around doin' nothin' for more than 15 years. Ditto for the digitizer plugins. Plus, I tested the instruments before parting them out and the relays were fine. |
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