Hi Ed,
>> Do you actually have a coax cable on the connector? Mine, and every picture I can find online, shows the power supply board as a single board
>> with the connector soldered directly into the board.
Yes, there is a connector that is indeed soldered onto the power board in my box as well. There are two other connectors though. At least, I would call them connectors too.
There is some wiring between the power supply and the oscillator, and these wires are soldered to a second connector, which mates with the connector on the power board.
And the coax I was referring to runs from that second connector to a third one (single line with regular 0.1" pitch) that plugs into the main board.
So, this morning I sat down to see if I could find some short or discontinuity in that part of the signal path. To my surprise, I found that there is a 50 ohm resistor
somewhere in the coax/connector assembly. I can not locate it exactly, but I would expect it to be at the end of the third connector.
After measuring, and checking again, I could find nothing wrong with the cable. So, in desperation, I hooked everything up, to see if I had perhaps missed something
in my earlier measurements. And to my astonishment, I now have an accurate 10 MHz signal at the third connector!!
Of course I am very happy about it, but I really have no clue what has changed to make that happen...
And now that it seems to work, it is impossible to find the fault...
I have hooked up my lowly Tek CDC250, which I have repaired some years ago by replacing the dead reference by a TCXO.
I have calibrated that reference with my GPSDO. It has been a while since I last used it (more than a year...), but when I hooked it up
to the Rubidium reference, and allowed for some warming up, it is giving a very steady 10,000,000 reading, with every now and then 10,000,001 .
Not bad at all!
A few remarks/questions in hindsight:
-Given your warning, I have taken a good look at the flex board, and it seems to be in excellent condition. No sign whatsoever in the direction of it being brittle.
-I found that the screws to mount the box on the base plate are just a bit too long, and they nudged a capacitor and bent it out of ts original orientation. i did not bend it back.
-On lifting the outer shell (after removing the four bolts on top), I found only two plastic washers. Are there supposed to be two, or four? Or perhaps none?
So, it seems that we can now shift attention to the "rest" of the PM6685.
And I agree completely, that is a entirely independent project in and of itself.
It is clear that the supply needs to be repaired or replaced, so I want to disassemble it from the counter, at least to protect whatever is still alive on the main board.
Heh, I was laughing when I looked at the video you posted: at 7:45, the guy simply lifts the supply board from the main board, effortlessly.
That will not be possible at all in my case! In fact, due to the construction, I think it is impossible to remove it without actually destroying one thing or the other.
During assembly, the board was mounted on the main board with nylon pylons, and then soldered in place on both ends at multiple pins...
So for disassembly, I see no other option but to destructively cut the pylons, and to make a jig from copper wire that allows me to heat all connector pins at the same time,
allowing me to desolder the board one end at a time. The heat sink close by does not make it any easier, though.
I truly wonder how they serviced the power supply in the factory.... And please do let me know if you can think of any alternatives!
If and when I can assemble a repaired or a replacement power supply back onto the main board, I will use nylon standoffs with ditto nuts and bolts!
>>Google is your friend.
Indeed it is, and I found the service manual without much difficulty. I am reading the relevant parts on the power supply.
And actually, the first thing I would like to do, is to power up the main board with a stand-in supply to see if there is still some life in it..
That replacement power supply would need to generate +5, +15, and -7 V, and the 5V is used as-is on the main board. Hmmmm.....
These supplies are not offered on FlukeBay. Fortunately, my unit already has the 2.7 GHz option and the GPIB option.
Thanks for the warning about doing measurements on the supply. I will be careful with that. But first it need to get out!