Re: Repairing my Tektronix 454 oscilloscope need some advice


Victor
 

Albert,
With the 454 energized today I could make some of your recommended test. I start with the "less risky test" and the results was far from my expectations. After follow your process I applied to Q1430 collector 1V pp and the voltage at the HV test point was only - 3 to - 4 V. I change the frequency from 23 kHz until 27 kHz and no results and no voltage increase to 77 V DC.
Otherwise: The current at F1437 measured is 0.22A. 
Also adjustment on pot R1401 give any variation on the HV test point.
The voltage on HV test point actually (in normal operation) is  - 64V. 
I could'nt make other test mentioned on your message on 02/17.
My test equipment is : scope TEK 7603, wave generator Sound Technology 3100A, meter Fluke 87III.
Any thought from your side ? 
Thank you 
Victor

-----Original Message-----
From: Albert Otten <aodiversen@...>
To: TekScopes <TekScopes@groups.io>
Sent: Tue, Feb 18, 2020 5:44 pm
Subject: Re: [TekScopes] Repairing my Tektronix 454 oscilloscope need some advice

(continued)
I did an easier and less risky test. F1437 tied to GND, wire to "P" disconnected. Sine wave generator FG504, same GND , 50 ohm output applied to Q1430 collector (no other termination). Viewed waveform at Q1430 collector at a scope. Kept amplitude pp up to only  1 V so  Q1430 would never conduct.
Measurements:
Resonance at about 23 kHz, not very sharp but clear enough.
Amplitude 1 V pp at collector resulted in 77 V DC at the HV test point as measured with a 10M DMM.
Impedance was about 10 ohm.

Albert

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