Tektronix 434 s/n below 500000 faulty ps.

[Craig]

Interesting. Qservice too.

[Nick]

I've bought from both Qservice and Sphere several times in the past and they are very good and helpful...

[johnmcgivern]

Hi, bit pricey how much p&p?
Attachment shows 940A voltages so hope these are good enough.

John.

   

[johnmcgivern]

Hi wee bit of luck been checking transistors as quite a lot are socketed.
Applied signal from generator and triggering stable apart from vertical green line from top to bottom and a horizontal faded line scrolling in Y direction bottom to top.
See photo.
When rotating intensity knob voltage varies from 8vdc to 89vdc.
Intensity too bright cannot reduce???
Any ideas.
Cheers, John.

       

[Craig]

TP924 does not sound right. According to the panels on the left, that should be at about 50V

[johnmcgivern]

I agree. Craig could you please write the set up for both scopes so I can test waveforms as I am not to sure.
Are the waveforms shown 1x or 10x probe?

Penny just dropped 940B is the rest of the pins on 940A doh.
Can't see pin1or pin 10 but voltages look ok.
Many thx, John.

[Craig]

I agree. Craig could you please write the set up for both scopes so I can test waveforms as I am not to sure.
Are the waveforms shown 1x or 10x probe?

It is all on page 8.2 of the manual.


Craig

[johnmcgivern]

Tried them settings but signal was walking.
Tp924 is ok when intensity mid position around 50volts.
-75 is too low. Measures -69.4
More testing tomorrow. Ha ha

[Craig]

Tp924 is ok when intensity mid position around 50volts.

OK - which implies that the A half the chip and the associated transistor network for TP924 are working.

Possibility is that there is a fault in the DC restorer (diode phut, transistor phut, capacitor phut etc), or there is a problem with the HT, which is handled by the chip B half and a resistor chain.

[Craig]

Incidentally, since you have a maximum brightness trace, you are using the position controls to put the trace off the top or bottom of the screen?