Products > Test Equipment
HP 8566B - What to look for?
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W4PJB:
I'm going to look at an 8566B tomorrow. I can power it up and inspect it, but I don't think I'll be bringing my 8665B to test it as it's a little large to carry :D

The unit supposedly powers up and displays no errors, anything else i should look for? If i set it for "full span", is there anything obvious on the screen I should see if it's got a fault? I know the noise floor will shift a bit every few gHz (and that's a good sign). Anything else I can test?

I do have an Anritsu MB2721B with TG I could use to create a signal up to 7gHz.

G0HZU:
Connect the 100MHz test signal (BNC) to the main RF input and see if it adjusts OK when doing the RECALL 8 and RECALL 9 tests in the manual.

You can also try running the automated error correction routine by connecting the 100MHz test signal (BNC) to the main RF input and pressing the blue SHIFT button and then press the big FREQUENCY SPAN button. This runs an automated self correction routine that aims to improve performance by correcting errors between the RBW filters etc.

This takes about a minute to run.

Also put it on a 10MHz span and look at the 100MHz test signal. There will be some wobble seen on the signal when a 10MHz span is selected. A poor unit will show more wobble than a good unit.

Make sure the 0-70dB attenuator works on all settings. Note that you have to press ATTEN 0 dB to get it to select 0dB attenuation. It won't let you select 0dB with the down arrow key.

Probably the best advice I can offer you is to not buy the 8566B unless you really do need the extra frequency range it offers. It's unlikely to be very reliable in the coming years so you can expect to have to take it apart to replace tired capacitors from time to time.
Also, the RBW filters may need to be aligned/adjusted as per the service manual. It is also very big and very heavy and the fan noise is very loud. They can also smell a bit musty if operated in a small room as the fans will spread the musty smell into the room.

I've still got my 8566B but I rarely use it. I upgraded to something more modern about 5 years ago. Better performance, less noise and much easier to move about!
KE5FX:
One thing you should look at is the CRT condition.  All display elements -- text, trace, graticule lines -- should be razor-sharp at all reasonable brightness levels.

The suggestion to hook up the calibrator and do a recall-8, recall-9, blue shift-W cycle, followed by a blue-shift-w command to inspect the results, is a good one.  Take the time to read about that in the manual beforehand.  It is unlikely that you will need to tinker with the RBW filters but if there is a problem, this procedure has a good chance of indicating it.  Watch the shift-W cycle while it runs, keeping an eye out for gross errors in filter skirt shapes.

Agreed that these units are likely to become more "maintenance-prone" going forward.  But at least you can work on them.  Mine will leave my bench shortly after I do, feet first.
G0HZU:
If at all possible, try powering it on from a cold start to see how it behaves. Normally, you are meant to leave it powered in standby for maybe 15-20 minutes before powering it on. This allows the 10MHz ref oven to warm up and also other circuits need to be warmed up before it will be able to achieve reliable control of the swept LO system.

However, if you deliberately power it on from cold it should report REF UNLOCK and OVEN COLD on the CRT display. If the analyser is in good health, this probably won't stop it from being basically functional on wide spans at least.

However, when I first purchased my 8566B about 14 years ago, it would misbehave badly if given a cold start. It needed about 30 minutes to warm up and be functional. It showed all kinds of strange behaviour onscreen when started from cold. It would drift badly and in its attempts to try and sweep correctly it even wildly changed the centre frequency (to negative frequencies!) and basically went crazy.

Over time this got worse and worse (almost certainly why the rental company sold it to me so cheaply) and it eventually refused to lock even when warmed up.

This was traced to several failed capacitors on boards involved in the YTO (YIG) tuned LO system. Once these were replaced, it was basically useable from a cold start.

It will also report the condition of the battery when you first power it on. If there is an issue with the battery it will show BATTERY on the CRT display.

There are also a couple of red status LEDs along the lowest edge of the front panel. These should turn off once the analyser is booted and running correctly. If one or both of them stay lit then the analyser has problems somewhere.
W4PJB:
Thanks everyone for your replies, they are all very helpful! I certainly appreciate the warnings about it's age. That is, of course, a downside. But it's also part of the hobby. I'm the type that learns by doing; I need a problem to solve, I can't just sit and learn from a book. So if happens to kick down the road, I'm ok with that... I'll learn something! Whether I can fix it or not. Either way, the 8566 is just such a cool piece of gear I'd be kicking myself i missed the chance to own one for a few hundred bucks.

I'll be sure to let everyone know how it goes!
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