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| Agilent 8753ES A24 Microwave transfer switch substitute |
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| inaxeon:
Swapped my couplers over, and the remaining problem has moved to port 2. So, your diode plucking method has fixed the switch. Thanks for that. No doubt others will find this advice useful too. I think the story of this instrument is becoming clearer: The CPU board died (repair story here: http://www.mattmillman.com/acquisition-and-repair-of-an-agilent-8753es/ ) so whoever owned it transferred some bad bits into it and dumped it. This is evident from both the switch and the port 1 coupler having felt tip markings on them in the same handwriting. Without even opening it I'm guessing that coupler is another exotic difficult-to-repair hybrid. |
| Joel_Dunsmore:
Feel free to start another thread on the coupler, (which is actually a bridge; I designed it at about the same time as the bridge). Normally S11 should be flat across the band, but the fact it goes up and down indicates it is likely a low-freq issue (like a bad contact). But for investigation (presuming port 2 is the bad one) show also S21 and S12. and show S22 with an open and a load. Then we'll open it up and probe a few bits to see what we find. Very happy to hear the diode-trick worked. |
| inaxeon:
Here is the thread: https://www.eevblog.com/forum/testgear/agilent-8753es-a21-test-port-coupler-repair/ I switched the bad coupler back to port 1 |
| inaxeon:
Back in here again. In the throes of trying to repair my switch I bought this 5086-7539 off eBay for 20 bucks. Seller described it as "intermittent" ... which turns out to be BS. It's not intermittent as far as I can see. The actual problem with it is that when Port 1 is in the closed state, it's not connecting through to the 50Ω termination, instead reflecting the input. I had a bit of a poke around and the voltages are up to a couple of volts different from side to side. Slim chance it's the control board, will look into it further. Either way, it's interesting to look at. Surprised to see the hybrid is quite a bit different to the one 5087-7067. Pictures attached! |
| inaxeon:
One of the GaAs switches is damaged. Bummer. Seller refunded me. I wonder how this one died... Unlike mine both of the input diode strings are OK, because both of the "through" paths works OK with no attenuation, so can't have been an RF overload that killed it. It's just the unwanted reflecting on port1 that's the issue. Still, it is actually useable as an overkill antenna switch or something. Sweet ;-) |
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