[Test-Equipment] HP 8640B fixed

[Glenn Little WB4UIV]

My original problem was an 8640B that the display is flashing all zeros.

Some offered some suggestions pointing mostly to the rebuilt of the output 
amplifier.

When I did a lot of reading of the manual, I find that a flashing display 
is caused by the "Phase Lock Tune" voltage being either high or low out of 
specification. This would indicate a problem with the PLL. When I opened 
the top of the 8640B, I was greeted by there being no +20 VDC. The fuse was 
not blown and there was no voltage at the input of the regulator. On close 
inspection of where the power transformer is mounted to the board, I see 
what appears to be cracks in the solder for most pine. When I reflow the 
solder with additional flux, both of the pins that provide the +20 from the 
transformer are very loose. I removed the transformer to find that these 
pins were broken where the enter the transformer. I got out the Dremel tool 
and ball mill after verifying that there is continuity between these pins. 
I drilled out the center of the pins, found some connector pins that would 
fit into the milled out area. Soldered these in and replaced the transformer.

When I reapplied power, I was greeted with +20 VDC and a working 8640B.

In my case the flashing display was caused by a loss of +20 VDC.

The 8640B must have been dropped or subjected to some severe vibration 
while in the hands of a previous owner. This 8640B was bought at the E 
place and has property tags indicating that at one time it was owned by the 
USAF.

So for less that $150.00 and a little work (less that two hours) I am the 
proud owner of a functional 8640B with option 001 and 003.

Surprising to me, the display does go to 1024 MHz and the doubler is 
verified to not be there. When I find some proper equipment I will check to 
see if it is actually generating at 1 GHz.

Thanks to all that responded with their suggestions. Just wanted to provide 
some feedback as to what the problem was.


73
Glenn
WB4UIV