After quite a bit of work with the front panel (see earlier post, massive transport damage), and repair of its most beautiful and complicated inner workings, the remaining item to be fixed: the main output connector (N-type connector). The original one, damaged beyond repair, and the bracket holding it, severely bent, and a broken-off screw stuck in it.

Screening through my parts stock, found a rather old but still good panelmount N connector. It has a slightly different inner construction (the original 8645A has a quite long gold-plated coaxial air-line in the connector; replacement connector has no gold plating), but within reason, this should not matter.

This how it looked before:

The bracket and assembly was fixed back home, in good old Germany, in the mechanical workshop, during xmas vaccation.

Now, looking at the result, quite pleased with the outcome of quite a few hours of work (and some expenses, for a replacement HP System 2 front panel frame, see earlier post):

Note that there are two handles now mounted to the unit, not so much for carrying it around (about 70 pounds!), but to protect the front panel.

The 8645A has been a real challenge. Not electronically, but with all the mechanical damage.

Most of the defective parts are now fixed or replaced, the last one missing:

The front connector and bracket, badly damaged – this will need to go back with me to Germany, don’t have the right tools here (anyone out there with a metal workshop, in the greated NYC area, let me know!). Will see if I can bend this back, or machine a replacement from aluminum alloy. Also, one of the screws is broken off and stuck in the thread – all pretty laborious to repair.

The temporary set-up – connected a SMA f/f adapter, to get the signal out.

Electronically, major success! Not going into any details for now, explaining the inner workings of the 8645A would take hours. But, it is now back to a stage where power can be supplied to the circuits, and watch out, this is the first result:

… after several minutes, still no change – checked the manual – and the self calibration can acutally take 5 minutes or more, so I am patiently waiting. Finally, this result:

Sounds good.

Went quickly through all of the basic functions, and the machine seems to put out almost +20 dBm over the full band, stays perfectly phase locked, and, as far as I can tell with the 8565A, it is pretty clean.

Machine under test –

– showing a ~1.7 GHz signal, FM modulated, 30 kHz depth, 1.5 kHz audio.

For now, repair-final check on hold, with more tests once the connector is back in place.

The many hours spent so far, certainly worthwhile,for a machine that cost about USD 39.5k in 1990, close to 90k nowadays… all its major capabilities, well described in the HP 1990 catalog.
8645a hp catalog 1990