Re: tektronix 2235 , blown switchmode

From: TekMan (and7_at_bigfoot.com)
Date: 07/19/04 

Date: 19 Jul 2004 01:04:10 -0700

Jim Yanik <jyanik@abuse.gov> wrote in message news:<Xns9528C97961AC3jyanikkuanet@204.117.192.21>...
> john <john@removeagent-j.thiscom> wrote in
> news:opsa8wpymt64p9b0@funkmeister.agent-j.com:
>
> > Hi Jim,
> > thanks to both you and Jules for the fast response
> > From what i see, the tranny (Q908)thats blown has completely blown
> > its top
> > off and i can understand why...
> > The fet blew, shorting gate to drain... hence all the current went
> > through this poor little guy ( Q908, to-92 package).. frying it, the
> > diode CR908 and R909.
> >
>
snipp..
> >> 151-1136-00 MTP12N10E 100V 0.16ohm 14.0A
> >> 151-1141-00 IRF730,STP300H 400V 1.0 ohm 5.5A
> >> 151-1151-00 IRF710/MTP3N40 400V 3.6 ohm 1.5A
> >> 151-1152-00 IRF820/MTP475 500V 3.0 ohm 2.5A
> >> 151-1171-00 BUZ71A/MTP15N05E 50V 0.12ohm 14 A
> >> 151-1214-01 IRF830 500V 1.5 ohm 4.5A
> >> 151-1245-00 MTP6N60E 600V 1.2 ohm 6.0A
> >> 151-1286-00 MTP4N80E/BUK456-800 800V 3.0ohm 4.0A
> >>
> >>
> >>
>snip..

Well, do as Jim proposes.
Followind steps are helpful if you have replaced all other parts the
other posters have mentioned.

You can check the circuitry following the hv smps simply by powering
the scope from a regulated laboratory DC supply: Locate the 1000 mikro
F (uF) cap on the board, apply approx. 45 v Dc from the lab supply /
1.5 A . current limit is very useful (CC/CV-mode lab grade supply).

Scope should power up now and be usable partly. HINT: No mains
connection for this trobuleshoouting, so unpluq the mains lead from
the scope!! Otherwise, you'll fry yourself or other pars ;-).

Be careful not to get more than 49 v DC in this step (or the crowbar
circuit will trigger).

If you have excessive current, check also the flyback diode in the
primary SMPS circuit. It's likely to blow, and causes a nasty short
circuit for the 1000 uF cap. A 200V 2 A fast switch ( < 80 nanosec)
diode will be a good replacement.

If the TL594 SMPS IC in the primary SMPS is blown, it can be replaced
with a TL 494 ( the 594 is a little bit harder to get, at least here
on the european continent).

hth,
andreas

Relevant Pages

  • Re: tektronix 2235 , blown switchmode
    ... > circuit will trigger). ... > diode will be a good replacement. ... > If the TL594 SMPS IC in the primary SMPS is blown, ... Jim Yanik ...
    (sci.electronics.equipment)
  • Re: tek 2235 scope p/s problem
    ... The circuit of the 2225 Scope is completely different to the 2235/2215 ...
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