I had sent a response earlier but it didn't appear to have made
it.
I checked some of the voltages on the board, but can't say I
entirely know what to make of all of them (newb alert again hah)
Ok,
I've got 94v on the unregulated rail
On the op-amp, pin 1 vref is 10.00v
Pin 2 from the voltage divider is reading as ~1v or just under. Pin 1 is
reading 15.19v.
Q1222: Emitter 8v, base is grounded of course, and
11.6v on the collector.
Q1220: (sorry, not sure which is
emitter/base/collector, I'd have to look up a datasheet - more newb showing
through). So looking down on the power supply as it's mounted in the chassis:
11.3v on the left pin, 94.7v on the middle pin (must be the collector) and
11.8v on the right pin.
Q1221: 94v on the collector, 11.1v on the base
and 10.6v on the emitter.
I didn't measure Q1223 - hard to reach that
one.
R1212: 94v on the unregulated rail side, 10.5v on the other side
of it.
R1220: 94v on the unregulated rail side, 9v on the other
side.
Curious how I got 15.19v on pin 1 of U1281A with a 10v ref and a
1v comparison from the voltage divider off the regulated line - looking at the
datasheet it looks like it should be operating as two separate op-amps with
one half regulating the 87v line and the other the 42v line, so I fired it up
again and checked the voltage on all of it's pins:
pin 1: 15.57v
pin
2: 1.05v
pin 3: 10.00v
pin 4: -6.86v
pin 5: 10.00v
pin 6:
1.58v
pin 7: 15.58v
pin 8: 16.42
So thinking about it for a bit,
the schematic shows a voltage of -1.53v for pin 1 (a far cry from the 15v I'm
getting)which I assume is the voltage I should see when the line is regulated
to 82v. And I assume then that the 16.42v is the positive power for U1281, and
the -6.86v is the supply that lets it pull Q1222 low when the voltage from the
voltage divider feeding pin 2 = the 10v ref from pin 3.
So I guess I
learned something, but as far as using the voltages to give me an indication
as to what's gone wrong I'm not sure. That will take a better man (or woman)
that's more educated than I! I would have to resort to the shotgun repair
method at this point - replace all the components :) (certainly not to the
point of wanting to shoot the scope yet lol)
As a note, when reading
these voltages they can vary a bit while checking them. Sometimes it's not
uncommon to see some of the voltages vary ~0.5v it seems, so that accounts for
some of the variance in the first vs 2nd measurements in areas. Earlier I was
reading ~9.5v on the 87v regulated line, but tonight it was just under
9v.
Thanks!
Chris
--- In TekScopes@..., "John
Snyder" wrote:
>
> Chris
>
> The CR1244 is across the
B-E junction of the transistor, so in circuit it
> would not measure
Open like a diode out of the circuit would.
>
> I have my board
out waiting for the inverter board to dry from it's
> cleaning, and I
measure .706V forward (of the diode) and .581V reverse
> (instead of
open, which is forward for the transistor junction.)
>
> You
could measure all the voltages Q1220, Q1221, Q1222, and Q1224 E,B and
C
> along with U1281A pin 1, 2 and 3 CR1220 anode to see what is out of
wack
>
> John
>
>
>
> -----Original
Message-----
> From: TekScopes@...
[mailto:TekScopes@...] On
Behalf
> Of Chris
> Sent: Monday, February 18, 2013 8:37
PM
> To: TekScopes@...
>
Subject: [TekScopes] Re: Tektronix 2465 capacitors etc.
>
> John,
> A HUGE thank you on checking that and giving me your value! I was
hoping
> the short wasn't in the main board somewhere as that doesn't
look like fun
> to pull in the least.
>
> I just checked
the resistance from the pin 7 (blue 87v wire) on the
> connector (power
supply still out and on the bench) and I got a value of
> 25.55Kohm, so
it would appear I should be OK to go at that (assuming that
> powering
something else up on the main board doesn't cause it to
> short/overload
the supply). I was testing the diodes on the power supply
> and diode
CR1244 is giving me 0.538V forward and 0.630v reverse. I think I
> might
pull it and check it out of the board later tonight after I eat etc.
>
> Thanks for the help!
> Chris
>
> --- In TekScopes@..., "John
Snyder" wrote:
> >
> > Chris
> >
> > The
problem could be in the 87V regulator
> >
> > Or
>
>
> > Their could be a short/low Resistance some where in the
load
> >
> > I have a 2465B open and I measured a load
resistance of 25.3K to ground on
> > Pin 7 of J121 (87V, the blue
wire) with the power supply unplugged from
> the J121 connector
>
> unit
> >
> > John
> >
> >
-----Original Message-----
> > From: TekScopes@...
[mailto:TekScopes@...]
On
> Behalf
> > Of Chris
> > Sent: Sunday, February
17, 2013 5:40 PM
> > To: TekScopes@...
>
> Subject: [TekScopes] Re: Tektronix 2465 capacitors etc.
> >
> > All voltages measured in the scope with everything hooked up. I
just got
> > done checking the voltages pre-regulator.
> >
> > At J233A I get:
> > pin 5 (87v unregulated)
97.6v
> > Pin 3 (42v unregulated) 49.0v
> >
> >
And at J234A I get:
> > pin 5 (15v unregulated) 18.94v
> >
Pin 4 (5v unregulated) 6.64
> > Pin 2 (-5v unregulated)
-6.92v
> > Pin 1 (-15v unregulated) -18.54v
> >
>
> Based on the unregulated values, I believe the issue must lie in
the
> > regulator portions, and since I'm getting the 97.6v
pre-regulated it would
> > seem to me the voltage doubler is working.
I also double checked and
> > verified the 10v reference voltage at
the test point on the main board as
> > well as the J121 connector
that feeds the main board. (I figured this was
> > important to
double check as the regulators all are based off the 10v
> >
reference as I read it). Of course this is where I wish to learn more -
I
> > understand what the individual components do but I still
somewhat struggle
> > to see what the assembly as a whole is doing,
which is why I'm trying to
> get
> > into all this, so maybe my
understanding is skewed. :)
> >
> > At any rate, it would
seem to me that with the unregulated voltages where
> > they're at,
that the issue would have to lie within the follow area:
> >
>
>
> > Yes? No? I mean I have the correct voltages on the left
side of those
> three
> > groups, and the wrong voltages on the
right side, so it would seem that's
> > where I should look
next?
> >
> > Thanks for helping this newb out!
>
>
> > Chris
> >
> >
> > --- In TekScopes@..., "Tom
Miller" wrote:
> > >
> > > The +87 is from a doubler
and added to the +42. I would take a close
> look
> > at the
three 10 uF caps and all the diodes in that area. Be sure to only
>
use
> > fast diodes for any replacements.
> > >
>
> > Since you recapped this unit, don't overlook the fact that
bad
> capacitors
> > can come from the factory new. Did you
measure all these voltages in the
> > scope or on an external
load?
> > >
> > >
> > >
> >
>
> > > Regards,
> > > Tom
> > >
> > >
> >
> >
> >
> >
------------------------------------
> >
> > Yahoo! Groups
Links
> >
>
>
>
>
>
------------------------------------
>
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>
