Hi everyone, the last time I asked a question I got some very good advice, so lets see if we have same luck this time.
I have the 1740A that I'm trying to restore, its in really good condition inside and out generally and certainly does not belong as landfill etc.
Last time I had distorted waveforms and your advice pointed me in the right direction and we resolved that issue and so while attempting to calibrate the scope a bit, the trace disappeared completely, did this a couple of times and never recovered. Pressing beam find confirmed that there was no HT.
Removed the HV cover and checked the supply rails coming in and all is correct but the oscillator is not running and I've confirmed this by using another scope and holding the probe in close proximity to the transformer and there is high frequency bleed at all. There is a 50Hz one if I turn the sensitivity all the way up, normally there is a high strength signal of around 30 to 40Khz but not on this one at present.
The voltages I'm getting on Q1, Q2 and Q3 are:
Q2?
Base? ? ? ? ?+16.8v
Emitter? ? ?+15v
Collector? ? 0v
Q1
Base? ? ? ? ?0v
Emitter? ? ?0v
Collector? ? +7.27v
Q3
Base? ? ? ? ?+7.27v
Emitter? ? ?0v
Collector? ? +22v
I should say as well that this particular board has the modifications to the Q1 and Q2 configuration which I have a photo of but not too sure how I can attach it in a fashion that you can see it, any ideas on how I submit the photo and on how I can resolve the oscillator issue?
All assistance is greatly appreciated.
Graham??
