HP 8559A repair

[idpromnut]

Several months ago I picked up an HP 8559A (with HP 853A display) for probably more than I should have. It needed a bit of work (there were a few broken wires in the SA module) and there is still an intermittent gremlin in the display power supply. The major thing that I liked about it and why I picked it up was the wide-band capabilities, 0.01 to 21GHz (in 6 bands).

Of course when I was testing it out, I actually run into a problem; only the first band (from 0.01 to 3GHz) worked and all the other bands displayed the same 3GHz band. I had put this problem aside since I didn't need anything higher than 3GHz for the moment. Today I decided to have another crack at trying to fix it. Looking at the service manual for the thing, I started working my way back form the front panel switches. They all tested out OK and the correct signals were being passed back into the frequency band selection board (A7). I pulled that board out and had closer look. That is when I found the problem: 2 "crushed" op-amps. They were most likely shorted out. These were used to adjust the YTO's driver for the higher than 3GHz frequency bands. The SA must have taken quite a knock to have done that!

[tautech]

And did a  fix it ?

[idpromnut]

And did a  fix it ?

A careful application of a leverage device (screwdriver) seems to have done the trick At least I can measure signals up in the 4.5GHz range now, which is better than before.

[tautech]

And did a  fix it ?

A careful application of a leverage device (screwdriver) seems to have done the trick At least I can measure signals up in the 4.5GHz range now, which is better than before.

Well you've a little way to go to 21 G  but thats gotto make you feel better.

I've allways been too to chase anyting like this for fear that you'd need another to fix it. 

[idpromnut]

The crazy thing was that it was sold "as-is" but the guy had said that it had been in good working condition when he had been using it a while back.    It looks like those two op-amps were the result of some shock to the side of the unit (perhaps even in shipping) but I hadn't opened up the unit that much when I got it, and there were no pictures of the inside of the unit before I bought it.