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Hi Bert. I was referring to the issue I emailed about a few days ago, and was asked to expand upon. I created a folder in the files section called TEK 465B woes that contains some images and a small move that really shows the problem.

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On 12/5/2014 1:37 PM, Kevin Crossett kcrossett@... [TekScopes] wrote:

Hi David. So the issue I am having with the scope is the trace does not go
all the way across the screen of the CRT of my Tek 465B.

Please expand on this:
(1) gap on the left side, (2) gap on the right (3) gap on both sides.
Have you tried the XY diagonal line test?
FWIW I once got a super deal on a Tek scope where the only fault in the
scope
was that one of the leads to the horizontal deflection plates was
connected to the plate pin.
The seller stated that it had bad CRT and it kinda.. sorta... worked.

The community has
helped me isolate the problem, thus far, to the horizontal amp section of
the scope. I have checked the voltages on all but the -2400 v power rail.
All check out to within spec so I don't believe the issue is with the
power
supply. The next step is to start tracing circuits to see if I can isolate
the faulty component(s) in the system that are affecting the display.
Raymond suggests checking the various transistors on the board, which I
plan to do. It does appear that the transistors on my particular unit are
soldered in place, not placed in sockets.

From your email, it seems I can check the transistors while they are
in the
circuit, which I will begin to do over the weekend. I assume the scope
needs to be powered on to make the voltage checks on the B-E and B-C
junctions. The service manual does have the pinouts so I will be referring
to the manual to ensure I am probing on the correct pins of each
transistor. I am also assuming that the transistors in question are easily
accessible on the bottom of the board.

[Non-text portions of this message have been removed]

[Non-text portions of this message have been removed]

Hi Albert. Appreciate the advice. I have checked the XY mode, but only with
no signal. The dot near the middle does move slightly, but only about a
half-an-inch or so. I don't have any way locally to create a triangular
wave form, and I don't have, or know anyone, with a second scope to use for
testing. I hope I don't need to desolder any of the transistors to check
them out. That would require some extensive disassembly, as far as I can
tell from looking at the physical component locations.

Hi Kevin,

Before desoldering anything I would first try to narrow down the possible faults. Did you try XY mode already? This mode comes in very handy since you must do with a DMM. To avoid a bright dot you can apply a signal (preferably triangular waveform) to Y (= CH2). Set X (CH1) to GND. With Horizontal Position you can move the dot (or vertical line) to the extreme left and right screen positions. These extremes correspond (nearly) to the start and end position of the sweep trace. Hence the start and end voltages for the sweep, given for test points 85 through 90 in the waveforms, are applicable. Now you can check the effect of Hor Pos at those three stages of the horizontal amplifier. Of course a fault in a stage has also effect further on, so look for the first occurrence of strange things. As said before and clear from the test point data, there is a lot of symmetry (balance) in the amplifier stages. Considerable lack of symmetry somewhere is a strong indication for a fault.

Albert

===========
Hi David. So the issue I am having with the scope is the trace does not go
all the way across the screen of the CRT of my Tek 465B. The community has
helped me isolate the problem, thus far, to the horizontal amp section of
the scope. I have checked the voltages on all but the -2400 v power rail.
All check out to within spec so I don't believe the issue is with the power
supply. The next step is to start tracing circuits to see if I can isolate
the faulty component(s) in the system that are affecting the display.
Raymond suggests checking the various transistors on the board, which I
plan to do. It does appear that the transistors on my particular unit are
soldered in place, not placed in sockets.

From your email, it seems I can check the transistors while they are in the
circuit, which I will begin to do over the weekend. I assume the scope
needs to be powered on to make the voltage checks on the B-E and B-C
junctions. The service manual does have the pinouts so I will be referring
to the manual to ensure I am probing on the correct pins of each
transistor. I am also assuming that the transistors in question are easily
accessible on the bottom of the board.

This will work if the power supply only operates on 240 volts AC. Using 120
volts AC requires both capacitors which operate as a voltage doubler.

Sorry, forgot to mention cause I use it for 230V AC operation.

Can anyone know if this PSU modification is correct?. I need to use one booster capacitor in place of two original Sprague.


Thank you Panos.

Hi David. So the issue I am having with the scope is the trace does not go
all the way across the screen of the CRT of my Tek 465B. The community has
helped me isolate the problem, thus far, to the horizontal amp section of
the scope. I have checked the voltages on all but the -2400 v power rail.
All check out to within spec so I don't believe the issue is with the power
supply. The next step is to start tracing circuits to see if I can isolate
the faulty component(s) in the system that are affecting the display.
Raymond suggests checking the various transistors on the board, which I
plan to do. It does appear that the transistors on my particular unit are
soldered in place, not placed in sockets.

From your email, it seems I can check the transistors while they are in the
circuit, which I will begin to do over the weekend. I assume the scope
needs to be powered on to make the voltage checks on the B-E and B-C
junctions. The service manual does have the pinouts so I will be referring
to the manual to ensure I am probing on the correct pins of each
transistor. I am also assuming that the transistors in question are easily
accessible on the bottom of the board.

I would be helpful at this point if you reviewed the problems and what you have
found so far.

The transistor junctions in many cases can be checked in circuit with a diode
test function. If a junction shows open in both directions, then it is bad. If
it shows shorted in both directions, then it is usually bad but not always; this
will depend on the circuit. If a junction shows open in one direction but high
in the other (it should be between about 0.5 to 0.7 volts), then it is bad.

On 12/05/2014 10:25 AM, Kevin Crossett kcrossett@... [TekScopes] wrote:

Thanks Mark. I ended up using a 470 uF cap rated at 250 volts. Turns out I
didn't need to perform the technique after all. In my haste checking
voltages, I missed the mV designation on my DMM. Looks like the voltages
are OK after all. Still, it was a great learning experience as now I know
how to check for faulty caps.

Good deal. Sounds like you're making some progress then. We have some pretty sharp folks here on this list, and I've gotten tons of help from them in the past. Don't be afraid to ask for help, it's freely given here.

Mark

Taylor, George,
Thank-you. This is greatly appreciated. I do have a question. I
didn't find a troubleshooting guide. Is there one buried in there
someplace? And a very big thanks to everyone who sent their suggestions.
It is greatly appreciated. I just have to round up some physical help to
move this thing around. I'm hoping that it will last for three more
weeks. I might be able to find a TV that has been set out on the curb.
But I have my doubts about whether this thing is going to last that
long. When it really started acting up it would take a minute or two to
start up and stay on. Up to yesterday it was taking 5 minutes to start
up. Well yesterday it took almost 15 minutes to start and stay on.
Thanks again all,
rich!

Did you try Talon Electronics? I get FREE yes FREE pdf service manuals from them, just for asking. George is the old timer there - be sure you put that in the contact form. I got an LG LCD manual from them around Halloween - no one else had it for free.

They also sell some Zenith parts.

Taylor

Thanks Mark. I ended up using a 470 uF cap rated at 250 volts. Turns out I
didn't need to perform the technique after all. In my haste checking
voltages, I missed the mV designation on my DMM. Looks like the voltages
are OK after all. Still, it was a great learning experience as now I know
how to check for faulty caps.

On Fri, Dec 5, 2014 at 5:17 AM, Mark Wendt mark.wendt.ctr@...
[TekScopes] <TekScopes@...> wrote:

On 12/04/2014 01:42 PM, Kevin Crossett kcrossett@... [TekScopes]
wrote:

That's what I figured. I will look in my junk box for an old power supply
or some other electronics gizmo for the 100 v cap. Assuming I find one in
the next day or so, I am now trying to determine the positive side of the
cap...
I found this image on the internet of someone with a similar problem as

me.

He laid out what he thought were the solder points for the 4439 cap. Is

he

right, and if so, how can I determne which one is positive?

You can also use a higher voltage cap too. Won't matter a bit. Just
don't go lower.

Mark


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Yeah, I'm pleased that the voltages are OK. I will begin checking the
connections over the weekend, but I will have trouble with the transistors.
I know some scopes use sockets for the transistors, but mine seem to be
soldered to the board. I suspect my scope is one of the "newer" versions
and I have heard that the company moved away from sockets at some point
during the production cycle. Is it possible to check the B-E and B-C
junctions while the transistors are still on the board? I have a DMM that
can check diodes so I suspect I could reach the pins.

On 12/04/2014 01:42 PM, Kevin Crossett kcrossett@... [TekScopes] wrote:

That's what I figured. I will look in my junk box for an old power supply
or some other electronics gizmo for the 100 v cap. Assuming I find one in
the next day or so, I am now trying to determine the positive side of the
cap...
I found this image on the internet of someone with a similar problem as me.
He laid out what he thought were the solder points for the 4439 cap. Is he
right, and if so, how can I determne which one is positive?

You can also use a higher voltage cap too. Won't matter a bit. Just don't go lower.

Mark

Well, the good news is that it seems you won't have to replace one or more of the large el. caps.
If you're now certain about the voltages you reported, I'd say the power supply voltages are good enough to allow the 'scope to operate correctly.
With your limited set of instruments (yes, you do need a 'scope to repair a 'scope), you may now try some easy things i.e. check and possibly swap some transistors and see what happens. However, I'd first check if the left and right deflection plate connections are ok. Check the wires and clips that connect the CRT. Be careful and only use low force on the CRT pins and *don't* bend them, even if they're crooked.
By swapping transistors, there is a slight risk that you'll damage a good transistor but replacements are available and not expensive.
Depending on your DMM, you may do a diode test on the B-E and B-C junctions on each transistor (they're all in sockets) and swap like transistors in the horizontal amp (schematic 10). The physical location of the horizontal amp. is on the same board as the large caps but near the front of the 'scope.
Looking at the schematic diagram, you'll see a lot of symmetry. You may swap Q4146 with Q4341, Q4150 with Q4342 and Q4273 with Q4274 but *not* Q4161 with Q4361 nor Q4169 with Q4362. Please check this before actually trying (check on the schematics and check for identical type numbers printed on transistors to be swapped.
Where swapping changes nothing, put the original transistors back to avoid any possible loss of calibratio, though the difference should be minimal. Switch power off before any swapping.
U4269 is a DIL package containing five transistors. It has a Tek number but is just a CA3086. You may check the transistors in U4269, making sure that the substrate (pin 13) is at the most negative level. A replacement would cost less yhan a dollar.


BTW, did you wiggle all transistors in the horizontal amplifier in their sockets? Many "repairs" are performed by doing this...


Raymond