--- In TekScopes@y..., Stan or Patricia Griffiths <w7ni@e...> wrote:
help.Do you think maybe a bad output transistor? thanks for your
pinsvoltage onMikeMaybe, Mike. Looking at my 454 manual, I see that the collectorboth Q394 and Q494 should be about 41-42 volts measured with avoltmeter.Also, I don't think the voltmeter should "load" the circuit suchthat thevoltage changes very much because of attaching the voltmeter.There are TWOsets of vertical deflection plate pins. Are you sure all FOUR
theamplifiersis to short together like points such as the upper and lower CRTdeflectionplates in order to force them to be at the same voltage. Thisshould forcethe trace to be centered vertcially and should not damage thecircuitry. Ifthe trace is centered with the CRT vertical deflection platesshortedtogether (this is also the same as shorting the collectors of
Q394verticaloutput stage transistors together), it is a very good indicationthat the CRTitself is good.
good.and Q494.If the trace is once again centered vertically, most likely Q394and Q494 aregood. Next, move the short to the base of Q374 and the base ofQ474. If thetrace is once again centered, most likely Q374 and Q474 are
thisYou canwork your way a stage at a time through the vertical amplifier
wireway untilyou do not get a centered trace. Now you are very close to theproblem andit is time to check for shorted or open transistors in thisimmediate area.Be careful not to brush ground with the loose end of the short
youwhile theinstrument is powered up and the other end is connected because
surewill havea LOT of destroyed transistors if you do that . . . Also, be
w7ni@e................................................................BOTH endsof the short wire are disconnected before connecting one end toanother partof the circuit . . .
signalhalf of screen and I have a small deflection of a square wave
haveso gain is poor. Should Q374and Q474 be a matched duo?
the Qgiven me. mikeHi Mike,
numbers was the one I now have up for sale on eBay right now. Youshould
look at auction #1226363944 and think about bidding on it.You can
test those for most defects with an ohmmeter right on the bench.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 theshorting process
to the previous stage, etc.......................................................................
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
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