Re: Tektronix 2235 Scope High Voltage Problem
From: TekMan (and7_at_bigfoot.com)
Date: 09/28/04
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Date: 28 Sep 2004 00:01:28 -0700
Jim Yanik <jyanik@abuse.gov> wrote in message news:<Xns9571D407F42C1jyanikkuanet@204.117.192.21>...
> and7@bigfoot.com (TekMan) wrote in
> news:6a624601.0409262333.1bb8b871@posting.google.com:
>
> > Jim Yanik <jyanik@abuse.gov> wrote in message
> > news:<Xns957089733DC52jyanikkuanet@204.117.192.21>...
> >> bobd426@yahoo.com (Scibuff) wrote in
> >> news:6fa04d1c.0409251726.6f1d16c@posting.google.com:
> >>
> >> > It looks like my faithful 2235 has bit ths dust! When powered on,
> >> > the power LED only pulses on/off about every second and the CRT has
> >> > no light. Using the Service manual, I got as far as restoring the
> >> > power LED operation by disconnecting the lead from T948-p23 to
> >> > U975, which I assume is the HV multplier, but have no details on
> >> > it. The 2 5.1K resistors off U975-p4 are good and disconnecting
> >> > C975 and C976 one at a time does not allow the Power LED to come on
> >> > steady.
> >> >
> >> > Help please!
> >> >
> >>
> >>
> >> The HV multiplier has a red lead that goes to the front of the CRT.
> >> The multipliers do fail occasionally.
> >> You will NOT be able to order one from TEK,they consider this model
> >> obsolete.A parts scope will be your only source,I believe.
> >>
> >> The HV mult develops the -2960 cathode V from the pin that feeds the
> >> 5.1K resistors,the anode V comes from the pin that the red HV lead to
> >> the CRT is connected to.
> >>
> >>
> >> Are your low voltages proper when you disconnect the HV mult.?
> >
> > The HV multiplier is a x6 type. Do as Jim proposed and try to get a
> > parts scope.
> >
> > It is possible to build the the HV multiplier from discrete parts
> > (diodes, caps, etc), but is really a tedious task and requires HV
> > expereince. I did it a couple of times, but would recommend this only
> > to someone with a lot of repair experience. The HV is nasty, so
> > careful soldering and isolation technique is a must.
>
> And you have to build it to fit into the available space and not arc to
> something else.
> >
> > you're better of with a commercial build multiplier from a parts
> > scope.
> >
> > hth,
> > Andreas
> >
>
> I believe the multiplier is a X-FOUR,not six. My 2215 schematic shows X4.
> I also believe he could adapt a HV mult from a 1700 series TEK waveform
> monitor,they're about the same size,but don't have the internal cathode
> supply diode,no big deal. 152-0900-00,and probably still available from
> TEK.
Special case was not necessary to prevent arcing. "Rounded" solder
blobs are much more important to prevent HV arcing due to corona
effects etc.
Insulation: A couple of spray paint named Plastik70 (a special brand
forHV, a german suppier manufactered this. Don't know if it is still
for sale).
Multiplier: It's a sixtupler ( x6 ) in the 2235, but a quadrupler ( x4
) in the 2215 - trust me :)
hth,
Andreas
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