HP 8663A help and suggestions

[rcowboy78]

So I picked up an HP 8663A for dirt cheap, and it serves me right because it's a basket case.

Short summary:
Power supply was toast. I have rebuilt all 4 power supply boards, and have got the machine up and running. Everything is running great up to its output so far. Currently I am chasing the following problem, and am stuck on what to do.

The output of jack J4 on board A4A3 is not correct. J4 should = 120 - 640 Mhz at 0dB. My output is all over the place from being right, to no output at all. It's intermittent.

Here's my problem: I have pretty much determined that the output amp for this section is fine, because J2 and J3 outputs are just fine and there outputs go through U5. J4 is the only one that's not correct. I would like to probe TP9 and TP2 and see if I get the proper signals there. However, to really probe these correctly I need either 500 MHz probes or better, or I need to run some coax out of this module and terminate it with SMA's, which then can go to a scope. In order to do this, I would have to drill a couple of holes through the mounting plates on the outside to get the coax through. I do not have the riser kit for this instrument, and frankly I haven't tried to source one.

I've attached an image of the schematic and picture of the board for your enjoyment. I though maybe someone could give me another suggestion on how I could probes these points without making a mess. The image is the best I could do with the small available size of pictures on the site.

Thanks for your help,
rcowboy

[rcowboy78]

Upon further inspection, I was able to detach the face plate to get the RG-174 through without drilling holes. Will see how it goes. Will make some SMA pigtails and probe that way.

rcowboy

[rcowboy78]

Test Point 2, beautiful.

Test point 9,  Now to find the problem. This could take a while.

rcowboy

[rcowboy78]

Okay, moved the pig tails to TP5 and TP8. Bad signal at TP5 and bad signal at TP8. Therefore the problem lies somewhere in the divide by 2 sections or CR1 pin diode.

I bet it's U3 or U4, and after a quick search I'm turning up empty for the part. It's some sort of NOR gate job with a flip flop. Could be a Capacitor problem, but unlikely since most of them are ceramic.

Anyways, will keep digging and see what I can do.

rcowboy