Actually, this is probably the place to ask, since I've been poking around this unit long enough without figuring it out. I'm certain it's something simple and stupid I keep overlooking, but I'm going to start with a brief history.
When I received the unit over 10 years ago, it had been well-used and abused by Verisuck employees; when it failed pretty obviously one or more of the trained ape brigade had taken it apart and tried to fix it. the DC-DC converter had several of the stacked epoxy-sealed Sangamo caps on the +/- 8.6V rails had cooked themselves to death, as had the big 4700uF on the 5V rail. It had shorted one diode in the line voltage bridge, which I was able to find only two of, so I replaced both on the opposing sides of the same cycle on the bridge, then I replaced every cap in the 42V DC-DC converter and low voltage inverter sections. It came back to life, everything was happy, and I used it for ~3 years without issue. Then the HV multiplier/Flyback failed, and it went in storage, got lost in a move, sent in, sent back, queried, lost, found, subjected to public enquiry, lost again, and finally buried in soft peat for
three months* several years while I located a replacement and then I eventually dug it out a couple weeks ago.
First thing I noticed when I was troubleshooting the HV was that it now had a loud whine; I assumed it was T948 in the HV complaning since the flyback had failed so thought nothing of it. When I replaced the flyback it persisted, and while the 'scope did come up, it had errors in the POST. So once I determined that the fault was in the Acquisition RAM, but only on the highest speed mode, my niggling feeling that the POST errors and the new noise were related came back to mind. After poking around with an insulated screwdriver with handle held against my ear (very cautiously too, as this model has 2KV potential in the same area
), I isolated the noise not to T948 in the HV, but to T906 in the 42V DC-DC converter.
Oy vey.
so my last few sessions have revolved around trying to isolate the source of the noise in the 42V DC-DC converter; so far, to no avail. Excessive noise floating on all DC rails except the +/- 8.6 rails (stacks of Sangamo 840uF caps) indicates to me that the problem must be somewhere in the converter; but even after removing all other caps and substituting, still no resolution.
Ideas? Cheers? Jeers? Something stupid you can see from a mile away?
I'm using the manual from Artek; it's better than the one hosted my the Tek affiliate. This site appears to have
a decent copy that passed my virus scans.
I think I'm going to go to Harbor Freight for some retail therapy now...
mnem
* shamelessly snurched from HHGTG