Tektronix 2235 Intensity problem

[John B]

Recently purchased a Tek 2235 (does not have military option). It displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control has no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies when
the 'B' pot is turned as well as the output voltage on the emitter of Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't see
any components with visible damage, but there is a place on the board that
is brown from heat around Q254, Q255, Q256 which is the Vertical output to
CRT section. I'm guessing that this is unrelated to the intensity problem.
any help or ideas would be greatly appreciated.

Thanks,
John

 

[Terry Ilardi]

John B wrote:

Recently purchased a Tek 2235 (does not have military option). It displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control has no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies when
the 'B' pot is turned as well as the output voltage on the emitter of Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't see
any components with visible damage, but there is a place on the board that
is brown from heat around Q254, Q255, Q256 which is the Vertical output to
CRT section. I'm guessing that this is unrelated to the intensity problem.
any help or ideas would be greatly appreciated.

Thanks,
John



John,

Did you ever get any information on this? I have the same problem on my
2235 and have just ignored it for several years (I bought it used and it
came that way).

Thanks,

Terry Ilardi

 

[Kevin Carney]

I wrote a good explanation to original question. Do a Google search.

--
change .combo to .com for correct email

***************************************************
"We ought always to know precisely why a given job
is done in a particular way, and why it is done at
all, and why it can't be done more efficiently,
if it must be done at all."-- T.J.Watson

***************************************************

"Terry Ilardi" <ilardi@us.ibm.com> wrote in message
news:c1vodm$gam$1@news.btv.ibm.com...

John B wrote:

Recently purchased a Tek 2235 (does not have military option). It
displays
both traces ok as well as a square wave on both channels. Both traces
respond to the 'A' intensity control, while the 'B' intensity control
has no
effect. Has anyone else experienced this problem? Both the 'A' & 'B'
intensity control pots check out ok. Voltage at the base of Q814 varies
when
the 'B' pot is turned as well as the output voltage on the emitter of
Q814.
Voltages here are correct too. There is no voltage change at the node of
anodes CR818 and CR820 while turning the 'B' pot, but it does change
here
when the 'A' intensity pot is turned. I've checked all related
diodes --CR818, CR820, CR805, CR817, CR816, CR680, etc., and related
resistors. Q586 is biased and stays on in "Ch1", "CH2", and "Both"
positions, at least as far as I can tell with the voltmeter. I don't
see
any components with visible damage, but there is a place on the board
that
is brown from heat around Q254, Q255, Q256 which is the Vertical output
to
CRT section. I'm guessing that this is unrelated to the intensity
problem.
any help or ideas would be greatly appreciated.

Thanks,
John



John,

Did you ever get any information on this? I have the same problem on my
2235 and have just ignored it for several years (I bought it used and it
came that way).

Thanks,

Terry Ilardi