Topics

454 with no vert. deflection


mtmpsmp@...
 

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance on
vertical plates and the trace is still centered!


Stan or Patricia Griffiths <w7ni@...>
 

mtmpsmp@yahoo.com wrote:

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance on
vertical plates and the trace is still centered!
Boy! I don't understand that either. I have to wonder if the voltage
unbalance is actually getting to the deflection plates inside the CRT.
Perhaps there is a broken connection INSIDE the CRT. If the unbalance is
actually on the CRT plates, I don't see how the trace can be centered
vertically . . .

Stan
w7ni@easystreet.com



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mtmpsmp@...
 

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
mtmpsmp@y... wrote:

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance
on
vertical plates and the trace is still centered!
Boy! I don't understand that either. I have to wonder if the
voltage
unbalance is actually getting to the deflection plates inside the
CRT.
Perhaps there is a broken connection INSIDE the CRT. If the
unbalance is
actually on the CRT plates, I don't see how the trace can be
centered
vertically . . .

Stan
w7ni@e...
.....................................................................
......................................................................
Stan,
Upon further investigation I have found that when the scope is
turned on the collector voltage is the same (74.6 volts) on each
output device. The voltage will stay in that condition ( flat
centered trace) until I start making voltage measurements with my
voltmeter ( high impedance digital) then the top connecter drops to
56.8 -62.0 volts and the bottom to 32.5 -29.8 volts, the voltage of
course being determined by position control. The trace is at this
point off screen in all modes ( chop, add ect) I can seem only to
bring this condition on by taking voltage measurement on either vert
plate.
Do you think maybe a bad output transistor? thanks for your help.
Mike


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Stan or Patricia Griffiths <w7ni@...>
 

mtmpsmp@yahoo.com wrote:

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
mtmpsmp@y... wrote:

I have a 454 that has no vertical deflection on ch1 or ch2, using
another scope I am able to trace signal from the preamps to the
deflection plates. The sweep appears to be in good shape and the
trace is centered on crt. ( position controls have no effect on
trace) What I don't understand is that I have a voltage imbalance
on
vertical plates and the trace is still centered!
Boy! I don't understand that either. I have to wonder if the
voltage
unbalance is actually getting to the deflection plates inside the
CRT.
Perhaps there is a broken connection INSIDE the CRT. If the
unbalance is
actually on the CRT plates, I don't see how the trace can be
centered
vertically . . .

Stan
w7ni@e...
.....................................................................
......................................................................
Stan,
Upon further investigation I have found that when the scope is
turned on the collector voltage is the same (74.6 volts) on each
output device. The voltage will stay in that condition ( flat
centered trace) until I start making voltage measurements with my
voltmeter ( high impedance digital) then the top connecter drops to
56.8 -62.0 volts and the bottom to 32.5 -29.8 volts, the voltage of
course being determined by position control. The trace is at this
point off screen in all modes ( chop, add ect) I can seem only to
bring this condition on by taking voltage measurement on either vert
plate.
Do you think maybe a bad output transistor? thanks for your help.
Mike
Maybe, Mike. Looking at my 454 manual, I see that the collector voltage on
both Q394 and Q494 should be about 41-42 volts measured with a voltmeter.
Also, I don't think the voltmeter should "load" the circuit such that the
voltage changes very much because of attaching the voltmeter. There are TWO
sets of vertical deflection plate pins. Are you sure all FOUR pins are
connected?

A good troubleshooting method for balanced circuits like vertical amplifiers
is to short together like points such as the upper and lower CRT deflection
plates in order to force them to be at the same voltage. This should force
the trace to be centered vertcially and should not damage the circuitry. If
the trace is centered with the CRT vertical deflection plates shorted
together (this is also the same as shorting the collectors of the vertical
output stage transistors together), it is a very good indication that the CRT
itself is good.

Next, you can remove the short and move it to the emitters of Q394 and Q494.
If the trace is once again centered vertically, most likely Q394 and Q494 are
good. Next, move the short to the base of Q374 and the base of Q474. If the
trace is once again centered, most likely Q374 and Q474 are good. You can
work your way a stage at a time through the vertical amplifier this way until
you do not get a centered trace. Now you are very close to the problem and
it is time to check for shorted or open transistors in this immediate area.
Be careful not to brush ground with the loose end of the short wire while the
instrument is powered up and the other end is connected because you will have
a LOT of destroyed transistors if you do that . . . Also, be sure BOTH ends
of the short wire are disconnected before connecting one end to another part
of the circuit . . .

Let me know how this works for you.

Stan
w7ni@easystreet.com


mtmpsmp@...
 

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:


mtmpsmp@y... wrote:

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...>
wrote:
mtmpsmp@y... wrote:

I have a 454 that has no vertical deflection on ch1 or ch2,
using
another scope I am able to trace signal from the preamps to
the
deflection plates. The sweep appears to be in good shape and
the
trace is centered on crt. ( position controls have no effect
on
trace) What I don't understand is that I have a voltage
imbalance
on
vertical plates and the trace is still centered!
Boy! I don't understand that either. I have to wonder if the
voltage
unbalance is actually getting to the deflection plates inside
the
CRT.
Perhaps there is a broken connection INSIDE the CRT. If the
unbalance is
actually on the CRT plates, I don't see how the trace can be
centered
vertically . . .

Stan
w7ni@e...
.....................................................................

....................................................................
..
Stan,
Upon further investigation I have found that when the scope is
turned on the collector voltage is the same (74.6 volts) on each
output device. The voltage will stay in that condition ( flat
centered trace) until I start making voltage measurements with my
voltmeter ( high impedance digital) then the top connecter drops
to
56.8 -62.0 volts and the bottom to 32.5 -29.8 volts, the voltage
of
course being determined by position control. The trace is at this
point off screen in all modes ( chop, add ect) I can seem only to
bring this condition on by taking voltage measurement on either
vert
plate.
Do you think maybe a bad output transistor? thanks for your help.
Mike
Maybe, Mike. Looking at my 454 manual, I see that the collector
voltage on
both Q394 and Q494 should be about 41-42 volts measured with a
voltmeter.
Also, I don't think the voltmeter should "load" the circuit such
that the
voltage changes very much because of attaching the voltmeter.
There are TWO
sets of vertical deflection plate pins. Are you sure all FOUR pins
are
connected?

A good troubleshooting method for balanced circuits like vertical
amplifiers
is to short together like points such as the upper and lower CRT
deflection
plates in order to force them to be at the same voltage. This
should force
the trace to be centered vertcially and should not damage the
circuitry. If
the trace is centered with the CRT vertical deflection plates
shorted
together (this is also the same as shorting the collectors of the
vertical
output stage transistors together), it is a very good indication
that the CRT
itself is good.

Next, you can remove the short and move it to the emitters of Q394
and Q494.
If the trace is once again centered vertically, most likely Q394
and Q494 are
good. Next, move the short to the base of Q374 and the base of
Q474. If the
trace is once again centered, most likely Q374 and Q474 are good.
You can
work your way a stage at a time through the vertical amplifier this
way until
you do not get a centered trace. Now you are very close to the
problem and
it is time to check for shorted or open transistors in this
immediate area.
Be careful not to brush ground with the loose end of the short wire
while the
instrument is powered up and the other end is connected because you
will have
a LOT of destroyed transistors if you do that . . . Also, be sure
BOTH ends
of the short wire are disconnected before connecting one end to
another part
of the circuit . . .

Let me know how this works for you.

Stan
w7ni@e................................................................
......................................................................
Stan,
I got no farther than Q374 and Q474,
I replaced both transistors and the output transistors collector
voltage dropped to 40.5 and 35.2 volts. The trace is now in the upper
half of screen and I have a small deflection of a square wave signal
so gain is poor. Should Q374and Q474 be a matched duo?
This thing about having to touch the collectors to start the
transistors to conduct is really odd, you don't have to leave the
probe on just make a momentary contact with deflection pin or
collector.
I don't have a manual for this thing so I'm working mostly in the
dark. I would like to thank you very much for all the help you have
given me. mike


Stan or Patricia Griffiths <w7ni@...>
 

Do you think maybe a bad output transistor? thanks for your help.
Mike
Maybe, Mike. Looking at my 454 manual, I see that the collector
voltage on
both Q394 and Q494 should be about 41-42 volts measured with a
voltmeter.
Also, I don't think the voltmeter should "load" the circuit such
that the
voltage changes very much because of attaching the voltmeter.
There are TWO
sets of vertical deflection plate pins. Are you sure all FOUR pins
are
connected?

A good troubleshooting method for balanced circuits like vertical
amplifiers
is to short together like points such as the upper and lower CRT
deflection
plates in order to force them to be at the same voltage. This
should force
the trace to be centered vertcially and should not damage the
circuitry. If
the trace is centered with the CRT vertical deflection plates
shorted
together (this is also the same as shorting the collectors of the
vertical
output stage transistors together), it is a very good indication
that the CRT
itself is good.

Next, you can remove the short and move it to the emitters of Q394
and Q494.
If the trace is once again centered vertically, most likely Q394
and Q494 are
good. Next, move the short to the base of Q374 and the base of
Q474. If the
trace is once again centered, most likely Q374 and Q474 are good.
You can
work your way a stage at a time through the vertical amplifier this
way until
you do not get a centered trace. Now you are very close to the
problem and
it is time to check for shorted or open transistors in this
immediate area.
Be careful not to brush ground with the loose end of the short wire
while the
instrument is powered up and the other end is connected because you
will have
a LOT of destroyed transistors if you do that . . . Also, be sure
BOTH ends
of the short wire are disconnected before connecting one end to
another part
of the circuit . . .

Let me know how this works for you.

Stan
w7ni@e................................................................
......................................................................
Stan,
I got no farther than Q374 and Q474,
I replaced both transistors and the output transistors collector
voltage dropped to 40.5 and 35.2 volts. The trace is now in the upper
half of screen and I have a small deflection of a square wave signal
so gain is poor. Should Q374and Q474 be a matched duo?
This thing about having to touch the collectors to start the
transistors to conduct is really odd, you don't have to leave the
probe on just make a momentary contact with deflection pin or
collector.
I don't have a manual for this thing so I'm working mostly in the
dark. I would like to thank you very much for all the help you have
given me. mike
Hi Mike,

You really need a 454 manual. The one I was using to remind me of the Q
numbers was the one I now have up for sale on eBay right now. You should
look at auction #1226363944 and think about bidding on it.

You probably have found at least one bad transistor, or maybe two. You can
test those for most defects with an ohmmeter right on the bench.

The next thing I would do is short the emitters of Q394 and Q494 and see if
this forces the trace to the center of the screen. If it does, then I would
say Q394 and Q494 are good and you need to progress with the shorting process
to the previous stage, etc.

You really need the manual . . .

Stan
w7ni@easystreet.com


mtmpsmp@...
 

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
Do you think maybe a bad output transistor? thanks for your
help.
Mike
Maybe, Mike. Looking at my 454 manual, I see that the collector
voltage on
both Q394 and Q494 should be about 41-42 volts measured with a
voltmeter.
Also, I don't think the voltmeter should "load" the circuit such
that the
voltage changes very much because of attaching the voltmeter.
There are TWO
sets of vertical deflection plate pins. Are you sure all FOUR
pins
are
connected?

A good troubleshooting method for balanced circuits like
vertical
amplifiers
is to short together like points such as the upper and lower CRT
deflection
plates in order to force them to be at the same voltage. This
should force
the trace to be centered vertcially and should not damage the
circuitry. If
the trace is centered with the CRT vertical deflection plates
shorted
together (this is also the same as shorting the collectors of
the
vertical
output stage transistors together), it is a very good indication
that the CRT
itself is good.

Next, you can remove the short and move it to the emitters of
Q394
and Q494.
If the trace is once again centered vertically, most likely Q394
and Q494 are
good. Next, move the short to the base of Q374 and the base of
Q474. If the
trace is once again centered, most likely Q374 and Q474 are
good.
You can
work your way a stage at a time through the vertical amplifier
this
way until
you do not get a centered trace. Now you are very close to the
problem and
it is time to check for shorted or open transistors in this
immediate area.
Be careful not to brush ground with the loose end of the short
wire
while the
instrument is powered up and the other end is connected because
you
will have
a LOT of destroyed transistors if you do that . . . Also, be
sure
BOTH ends
of the short wire are disconnected before connecting one end to
another part
of the circuit . . .

Let me know how this works for you.

Stan
w7ni@e................................................................

....................................................................
..
Stan,
I got no farther than Q374 and Q474,
I replaced both transistors and the output transistors collector
voltage dropped to 40.5 and 35.2 volts. The trace is now in the
upper
half of screen and I have a small deflection of a square wave
signal
so gain is poor. Should Q374and Q474 be a matched duo?
This thing about having to touch the collectors to start the
transistors to conduct is really odd, you don't have to leave the
probe on just make a momentary contact with deflection pin or
collector.
I don't have a manual for this thing so I'm working mostly in the
dark. I would like to thank you very much for all the help you
have
given me. mike
Hi Mike,

You really need a 454 manual. The one I was using to remind me of
the Q
numbers was the one I now have up for sale on eBay right now. You
should
look at auction #1226363944 and think about bidding on it.

You probably have found at least one bad transistor, or maybe two.
You can
test those for most defects with an ohmmeter right on the bench.

The next thing I would do is short the emitters of Q394 and Q494
and see if
this forces the trace to the center of the screen. If it does,
then I would
say Q394 and Q494 are good and you need to progress with the
shorting process
to the previous stage, etc.

You really need the manual . . .

Stan
w7ni@e...
......................................................................
Stan,
Well I have located a manual, I bid on the one you had on Ebay but
it got out of hand in short order! ( I know you were happy!)
Anyway I have located my problems. (plural) turns out someone had
lifted the end of D388 to check it at some time and the choke on the
back side of the board had come off. Also Q388 was bad I replaced the
transistor and resoldered the choke and things got interesting! The
position controls were working but gain was still way off. I started
checking for gain in each stage from the delay line and
got as far as Q 464,364 at this point gain fell drastically! :( Well
I Pulled those and low and behold they were npn not the expected pnp,
I replaced with two 151-0193 and I have a new scope!!!!
(This scope came from IBM so I really don't Know what to think about
this?)
So in closing I want to thank you for all your help It was very nice
of you to take the time. Now I have this 2213 that the trace only
covers half of screen........
thanks. Mike Smith


Stan or Patricia Griffiths <w7ni@...>
 

Hi Mike,

Good news! It is always great to hear of a success like yours.

More comments below . . .

mtmpsmp@yahoo.com wrote:

Stan,
Well I have located a manual, I bid on the one you had on Ebay but
it got out of hand in short order! ( I know you were happy!)
Anyway I have located my problems. (plural) turns out someone had
lifted the end of D388 to check it at some time and the choke on the
back side of the board had come off. Also Q388 was bad I replaced the
transistor and resoldered the choke and things got interesting! The
position controls were working but gain was still way off. I started
checking for gain in each stage from the delay line and
got as far as Q 464,364 at this point gain fell drastically! :( Well
I Pulled those and low and behold they were npn not the expected pnp,
I replaced with two 151-0193 and I have a new scope!!!!
(This scope came from IBM so I really don't Know what to think about
this?)
Well, there are marginal technicians in every company . . .

So in closing I want to thank you for all your help It was very nice
of you to take the time. Now I have this 2213 that the trace only
covers half of screen........
Half the screen horizontaly or vertically? I might have some ideas on this,
too, if you are stuck . . .

thanks. Mike Smith
OK, Mike. My pleasure.

Stan
w7ni@easystreet.com


mtmpsmp@...
 

--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
Hi Mike,

Good news! It is always great to hear of a success like yours.

More comments below . . .

mtmpsmp@y... wrote:

Stan,
Now I have this 2213 that the trace only
covers half of screen........
Half the screen horizontaly or vertically? I might have some ideas
on this,
too, if you are stuck . . .

thanks. Mike Smith
OK, Mike. My pleasure.

Stan
w7ni@e...
......................................................................
The trace starts on center of screen and runs to right side, Vertical
seems to be ok. The output transistors voltages are comparable but
signal on + plate is very weak. I don't have manual for this one but
layout looks very close to my 2235 .
although parts are numbered different.
Mike