Electronics > Repair

Tektronix SC504 HV multiplier

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Doug Brewster:
I'm in the process of dis-assembling a bad HV multiplier out of my SC504 to try and discover what's in it. I'm about 3mm in and have encountered what appears to be a couple of caps and the ground connection. What I'm looking for is info from any previous efforts in this forum to repair these devices in the hope it will save me work; the 3mm progress I've made so far using engineer's burrs in a dremel type drill has cost me an hour of dusty work so far and of course the damage done can make the internals unrecognisable as I found when doing the same job (happily successfully using info from the forum) in my 475, actually a couple of them.

Any ideas where to look? I'm new to this forum and haven't found my way around yet...

floobydust:
I don't see anyone taking these apart and reverse engineering them.
Tek465 HV multiplier replacement https://www.eevblog.com/forum/repair/tektronix-465/msg672083/#msg672083

All you need to know is how many stages, and capacitor value for the HV multiplier, in 152-0634-00 or CMX222.
I've used a heat gun to basically roast epoxy potting compound and soften it enough to pry off with a screwdriver, to read component values.

Most are 4-6 stage, 1nF or 1.4nF 10kV, BY8212 Philips diodes 12kV 5mA.

I would use 2CL74 (14kV 5mA) to 2CL77 (20kV 5mA) fast-recovery HV rectifier diodes and 2,200pF-10,000pF caps.

There's some x-ray pics, (URL ending in pic #1-6 of link) of a Tek 465 multiplier insides.
The HV connector is the valuable part to salvage.

edit: fixed url

Doug Brewster:
Thanks floobydust for the response. I  think it's a triple multiplier based on the SM info of 3.3KV pk input and 10KV (undefined) anode voltage. Trouble is the housing is about 1 cubic inch in size and it's going to be pretty crowded in there to get the parts in. I haven't tried the heat gun approach, maybe I'll give it a shot...

chris_leyson:
U1590 152-0634-00 VOLTAGE MULTR:HV MULTR, 6.7kV IN, 10kV OUT. Description in the service manual reads,
"The accelerating potential is supplied by voltage tripler U1590, having an input voltage of approximately 3.3 kV peak."

So the "6.7 kV IN" in the part description is pk-pk voltage. Same multiplier is also used in the SC502.

David Hess:
Annoyingly depending on the documentation, Tektronix might refer to the same high voltage multiplier as 1.5x or 3.0x.

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