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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Thu 14, 2019 6:41 pm 
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Location: Morristown, N.J.
I was the factory service engineer for the 8660 series for many years. I've forgotten much but maybe still have some useful info.
The "D" version is by far the most superior and reliable model. The only difference between the C and D is the "control" head and processor. I've converted many C's to D's in the past, a very simple task.
The "B" models should be avoided at all costs. Beyond the underrated IC's in the control head, there are many other problems.
From the highest output level (+10) down to 0dbm there will be a clunk of the attenuator switching internally. You should hear the same clunk going all the way down in ranges. To see that the output is switching properly you really need a spectrum analyzer. There are sometimes problems with attenuators opening. When these places are found its not anything to loose sleep over and I can guide you with a PM; I literally fixed hundreds and hundreds of them to avoid charging owners huge bills for replacement modules, all while working at HP.
I'll monitor this post to see if I can add anything as things come up.

Just recalled: in a 86602 and 86603 there may not be an attenuator switching between the highest output ranges. At this level the extra output power comes from the internal leveling circuits, not the attenuator. The 86601 switches an attenuator. I just hope I have this right!

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Thu 14, 2019 9:38 pm 
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Makes sense Pete. There is a problem with the metering which either goes back to a detector, ALC loop or meter amplifier. Meter barely moves off scale. Hopefully it not a blown RF amplifier.

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Fri 15, 2019 3:30 pm 
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Well, I tried a 88602A RF head and it works. The last two steps on the output range switch act the same as the 2.6 GHz head -- no loud relays clicking in the attenuator between those steps. RF level follows the positions, however.

Unfortunately, using a walkie talkie as a gauge for RF radiation, the 86602A is working fine. Lots of RF into a paper clip. I'd guess the 86603A is many dB down, at least 30 or 40 dB, and there is no RF meter indication, although the "vernier" control has some effect on the output level. I'll need to get my bench back and also I am waiting for a hard copy of the manual. I'm expecting the worse for this one. The 86632B had a bad meter. I'd almost suspect the dealer loaded the unit with bad modules except the property and cal tags all matched. The 8660D seems to be working, and that was the main concern.

Pete

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Sat 16, 2019 1:19 am 
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Peter,

I hate to admit this, but Pete's response to your question, made me go check my generator again, because I knew it clicked. "it clicks" alright, but thats because the dummy had the wrong module plugged in!!! I put in the 603 in, and there WAS NO click. I'm sorry for the stupid misleading mistake.

Check your PMs.

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Wed 20, 2019 5:32 am 
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Question for Peter: I have two RF heads that are showing very low RF output level on the meter, and the output does appear to be low. 86601A and a 86603A both show the same problem. A 86602A module works fine. What is the most likely cause for similar failures in these RF units? Hopefully not one of the HP sealed RF amplifiers! I do not having the service kit, so making measurements will be hard.

Pete

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Wed 20, 2019 4:45 pm 
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The only practical way to service an 8660 series is with the 11707 Test Plug-in. That plug-in pulls all of the oscillators out to the front panel, most importantly the 3.95-4.05GHz and 2.75-3.95GHZ oscillators. The only oscillator that you can't see with this plug-in is the 4.43GHz oscillator. These 11707A's are often on eBay. Also, if you don't have a microwave counter, an old cavity tuner will work just fine; you don't need very high resolution and the cavity tuners are very cheap (you will also need a crystal detector and a scope with tuner).

Just found a 11707A on eBay; its not mine! If you have an 8660 and it needs alignment you would be foolish not to buy this. https://www.ebay.com/itm/HP-Agilent-117 ... :rk:6:pf:0 I have nothing to do with the sale of this item. Repeat, it is not mine.

If someone doesn't have a modulation section, an inch of buss wire can be substituted for the plug-in but you won't be able to modulate. Even so, an external mixer (HP 10514) placed on the RF output will let you AM nicely.

If you hadn't realized it yet, the final RF output is a mixture of the 3.95-4.05GHz and 2.75-3.95GHz oscillators. But, these two oscillators float on the very unstable 4.43 GHz oscillator. The result of all of this mixing is that all of these microwave oscillators appear very unstable. Don't get the idea that they are solid when using a counter- they will drift all over and that's normal (as long as they all drift identically and are phase locked to each other).

Now that everyone is confused, I'll go back into hiding.

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Wed 20, 2019 4:57 pm 
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In my post above is used the wrong nomenclature for the Hp cavity tuners. The models needed are "Frequency Meters", 536A and 537A". These things are not light weights, but are a whole lot cheaper than a counter.

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Wed 20, 2019 5:42 pm 
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Thanks Pete.... I've seen those before... he asking top dollar; I'd make an offer but I'd really like to find the extender cable as well. One guy in Germany had the whole setup for less than what that seller is asking. I'll keep an eye out for one, or ask on the HP discussion group. The 86601A "fixed" itself. Output slowly recovered overnight, I suspect a bad cap or poor electrical contact needs attention. My spectrum analyzers will cover the GHz oscillator ranges, as will the the 5345A if I get it working.

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Wed 20, 2019 8:16 pm 
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Location: Morristown, N.J.
The attenuators used in these models are essentially identical. The open condition stems from a glue/cement that was used to hold in place some plastic screws. Over the years, the glue migrates microscopically onto the RF contacts and thus opening after a period of intermittent operation. When it comes down to cleaning these contacts I can instruct anyone in the process; its not rocket science but you've got to be careful.

I have one or two attenuators collecting dust in my cellar. If needed I can remove and mail any individual attenuator cards to anyone needing them. The only reason anyone would need to replace a card is because of a lack of care in the reassembly process. Don't break these; let me give you the proper steps. Much to the dismay of HP I quietly serviced no less than 1000 of these attenuators for free and spanning decades.

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 Post subject: Re: HP 8660D 86603A 86632A repairs
PostPosted: Feb Sat 23, 2019 3:52 pm 
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HP-86603A--I am seeing two different versions. One has a push-button in the lower left front panel to disable the frequency doubler for 650 to 1330 MHz. Why was this done?

Pete

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