Stan or Patricia Griffiths <w7ni@...>
--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:Maybe, Mike. Looking at my 454 manual, I see that the collector voltage onmtmpsmp@y... wrote:onI have a 454 that has no vertical deflection on ch1 or ch2, using
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
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.