Hi Tom,
Thanks for your mail. I popped the case off and probed the
points and found the voltages were all in tolerance. Excellent.
I'll
use it to assist in fault finding / audio design.
Many
thanks,
Brian.
--- In TekScopes@..., "Tom
Jobe" wrote:
>
> Hi Brian,
> Do yourself
a favor and at least check the various low voltages and the ripple on each
one.
> I think you have access to the low voltages by just taking the
outer cover off of the scope. I think there is a window in the metal frame on
the right side where the voltage test points are. You can also get to them on
the bottom side of the mainboard without removing anything else.
> The
scope depends on the accuracy of the various voltages to perform properly, and
all of the low voltages are regulated from the -8.6 volt supply in some
way.
> tom jobe...
>
>
>
> ----- Original
Message -----
> From: briankvedaras
> To: TekScopes@...
> Sent: Tuesday, June 26, 2012 4:00 AM
> Subject: [TekScopes] Re:
Q9070 Mounting in a 2220 - the news - the good news .....
>
>
>
>
> I have put in the IRF830, properly mounted to the
heatsink for Q9070. I put the scope back together with all covers in place,
believing and hoping that nothing else was blown and with my fingers crossed,
replaced the fuse......and switched on.....and it worked, fan on, no signs of
warm case, and it has now been on for 30 minutes plus.
>
>
> Thanks to help from Tom Miller, Tom Jobe and Ed Miller, who replied
to my posts re how to mount the FET.
>
>
> The question is
- as all appears to be working and stable, and cool, do I just leave it, or
would you recommend case-off and probing around to check for anything that
might be 'on the edge'....what do you learned gentlemen recommend????
>
>
> I am of the 'if it ain't broke don't touch it' school
(learned after some disappointing experiences), if you know what I mean.
>
>
> I have now got to read the instruction manual as to
how to use the storage scope element (just to see if it works - it does appear
to be doing some capture.
>
>
> Thanks in advance for your
replies to date, and I await with bated breath for your pearls of
wisdom.
>
>
> regards,
> Brian.
> --- In TekScopes@..., "Tom
Jobe" wrote:
> >
> > Hi Brian,
> >
My guess is that the IRF830 will work just fine.
> > Q9070 is so easy
to change that you could replace it later if you were so inclined.
>
> As for your need for an isolation transformer, I doubt that you will need
one.
> > If the inverter works, there is nothing else that really
needs to be tested unless you are just interested in the details, and a DMM
will give you much of that.
> > tom jobe...
> >
>
>
> >
> >
> >
> >
> >
> >
> >
> >
> > ----- Original Message
-----
> > From: briankvedaras
> > To: TekScopes@...
> > Sent: Sunday, June 24, 2012 12:47 PM
> > Subject:
[TekScopes] Re: Q9070 Mounting in a 2220 - help please (EASY ONE - I
HOPE)
> >
> >
> >
> > Tom,
> >
> > Excellent pics, thanks and very helpful.
> >
>
> I have the IRF830 (two spares were given to me with the scope), will they
do OK?
> >
> > --- In TekScopes@..., "Tom
Jobe" tomjobe@ wrote:
> > >
> > > Hi Brian,
>
> > Attached are some pictures showing how Q9070 is mounted.
>
> > On the original scopes there is no mica washer, just ordinary white
thermal paste on both sides of the ceramic piece.
> > > I think
your added mica piece might upset the clamping action of Q9070 to the aluminum
heat sink plate, but that is just a guess.
> > > One common
replacement for Q9070 seems to be the IRF840 (8 amp, 500 volt), they have
worked perfectly for me.
> > > tom jobe...
> > >
> > >
> > >
> > >
> > >
----- Original Message -----
> > > From: briankvedaras
>
> > To: TekScopes@...
> > > Sent: Sunday, June 24, 2012 7:49 AM
> > >
Subject: [TekScopes] Q9070 Mounting in a 2220 - help please (EASY ONE - I
HOPE)
> > >
> > >
> > >
> >
> Hopefully this will be easy for you experts out there.
> > >
> > > I recently bought a faulty 2220. It had been repaired with
some difficulty by the previous owner, he replaced some of the bridge
rectifier diodes (at least one was S/C, he also rings Q9070 and Q908 as items
that he replaced. The scope is in good condition, and the repairs look good
quality.
> > >
> > > After he repaired it, it ran
stably for several days with the case off. He then put the case on, and
within/after 1 hour the main fuse on the back panel blew big time (metallic
vapour on inside of the glass tube)
> > >
> > > A
quick look inside shows Q9070 short circuit, I checked the bits that had blown
before and they seem ok. The molex or similar plug to the pins of Q9070 look
light brown (has previously cooked).
> > >
> > > So
it looks like the PSU was working pretty much OK to have survived for that
long, and it was heat that pushed it over the edge. I found that the FET
itself was clamped between a brown plastic box and white ceramic type block,
with a small mica washer in for good measure. Q9070 is an IRF830. I tool the
fet out to have a look at it without paying too much attention to how it was
mounted, but I do know that I only needed to slacken the screw slightly for it
to come out (the body of the FET was not 'inside' the box).
> > >
> > > I believe that the FET may have been clamped ONLY on the
tab, and that the rest of the body of the FET was not in contact with the
heatsink or bracket. If that is the case, it may have run hot, but not too hot
with the case off, but with the case in place it overheated and blew.
>
> >
> > > Can one of you learned guys please tell me how
the fet should mount please, particularly including orientation of the brown
plastic box, the ceramic block, and the mica washer.
> > >
> > > The brown box looks like it could take the transistor in a
couple of ways:
> > > 1+ one with the mounting screw going through
the hole in the tab but then the ceramic block doesn't seem to work, and the
tab would not be insulated from the metal heat sink.
> > > 2+ with
the FET inside the box with the metal side facing the heatsink, with the
ceramic block sitting also inside the plastic block but being sandwiched
between the FET back and the heatsink.
> > >
> > >
Option 2 seems favourite, but I can't verify from the service manual. What do
you guys think of the right way to do it, and would it in fact need a mica
washer? My thoughts are not needed, just some heat transfer compound on either
side of the ceramic block.
> > >
> > > Any help
appreciated.
> > >
> > > Finally, re the scope
testing, I have a DVM and another working scope, so intend to make some
measurements, hopefully once I've replaced and remounted Q9070 and it works. I
don't have an isolation transformer, however, and remember from my younger
days of using a scope with 2 channels in add mode, and no 'gnd' connection
being made to the scope. Just channel 2 being put to the negative rail, and
channel 1 going to the point being measured, would effectively give me an
isolated scope. Does that make sense, and is there something to watch out
for?
> > >
> > > Thanks in advance,
> > >
Brian.
> > >
> > > As a new scope owner I am
>
> >
> >
>
