Thank you, Yves, about working on lower section.
I now wish I had made photographs of top-of-bottom, and bottom-of-top areas. There is a panel separating the two sections, with ~8cm x ~15cm opening near front for wires to pass top-to-bottom. I wish HP had used flexible cable for RF between the sections (two cables), this would make separating the sides easier.
Fortunately, when I was re-assembling, the two UT141 section connectors arrived very close to original position (I had not applied stress during dis-assembly), so there was no worry about reversing the two connectors (which go to switches next to the output step attenuator.)
After repair of 8673D, I tested output using my Tektronix 2755AP analyzer (I have had since ~2015, also old machine almost ready for scrap pile) to look at very narrow span (down to 100 Hz/div) for spectral purity. Tektronix 2755AP analyzer is providing error messages (about IF2 frequency control, it is strange "frequency locked loop" under control of firmware, and it is not PLL!) so it is next big machine for repair here. Adjustments are made with many many many small potentiometers, guided by primitive firmware. New adventure!
Some flat head screws inside (which are in many places along both sides of HP 8673D) are M4 x 4mm. I believe HP used many metric fasteners. I ordered some for spares, because of course it is easy to permanently lose specialty fasteners!
On the output connector (HP part number 08673-60040), it is used in other units, including HP 83595A and 83594A plug-ins for HP 8350A/B, it is used in HP 5348A counter/power meter (which is strange animal, like power meter with no option to set correction factors, and frequency counter, in same box, but with zero integration except shared LCD digits (????), and also connector is used in HP 5343A frequency counter, HP 8563E Opt 026 spectrum analyzer (and other/newer models). From the part number, I believe HP 8673 series was first requirement for front panel 3.5mm connector.
I searched for long time to find spare 08673-60040 connector, it is not so pretty, but it is working OK. Now there is one for sale on auction site (by supplier in israel), but cost is very high. Perhaps create search trigger for part number, after some time I think another will appear.
There is other kind of 3.5mm panel connector from HP, 08513-20017. It is I think used in modular plug-in microwave test equipment (HP 7000 mainframe), it is much lower cost connector on used market. I do not know if bulkhead hole diameter is compatible, but it is possibility. The original connector type is more rugged against damage (but as you found and I found, damage is still common.)
So, thank you for dialog about HP 8673D service adventure, and it is nice machine, almost weighs as much as adult person!
Dave
