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HP 339A oscillator problem
HP 339A oscillator problem
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Old 21st August 2018, 07:09 PM   #141
microx is offline microx  Spain
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R21 and R22 both measure 176K colour bands are very faint cant read and cannot find any Manual Change
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Old 21st August 2018, 07:21 PM   #142
BSST is offline BSST  United States
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Interesting. These two resistors are both 24.9K on my schematic. No worries. Let's repeat a VM test from a while back: if you place VM leads between TP1 and U3C pin 9, difference should be less than 10 mV. Same should be true at TP2 vs. U5D pin 9.
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Old 23rd August 2018, 01:05 PM   #143
microx is offline microx  Spain
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TP1 to pin 9 U3 +128mvdc. TP2 to pin 9 U5 +7.7vdc
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Old 23rd August 2018, 01:41 PM   #144
BSST is offline BSST  United States
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Sorry to hear of continuing troubles.

TP2 obviously not working, highly probable TP1 not working either. It you'd like to trouble shoot without resorting to component removal, we try.

As a check for at least partial opamp health, try measuring U3B (i.e.TP1) by using meter probe to join pins 7 and 6 simultaneously. This will produce unity gain and you should see 0V on meter if that opamp section is operable. Try same procedure at U5B.

If these checks look good, would you report opamp U3C voltages at +,-, and output pins, and Q1 base and emitter voltages? Similary, U5D and Q2?
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Old 23rd August 2018, 05:06 PM   #145
microx is offline microx  Spain
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ooops, my mistake counting pins the wrong way rou.

TP1 to pin 9 3mv. Tp2 to pin 9 jumping up and down from zero to 300mv

!!! found broken track between U5 and TP2, now TP2 to pin 9 3mv

Last edited by microx; 23rd August 2018 at 05:22 PM.
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Old 23rd August 2018, 05:53 PM   #146
BSST is offline BSST  United States
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Excellent sleuthing!

Good luck and please keep apprised of your progress!
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Old 23rd August 2018, 06:44 PM   #147
microx is offline microx  Spain
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Test 3-52 can now be performed, only the very low frequencies are unstable. The null with ext osc for 1kHz comes in at 1,100Hz. It more or less works now, how well is another thing
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Old 23rd August 2018, 06:54 PM   #148
BSST is offline BSST  United States
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Progress!

Don't hesitate to follow your own instincts, but I would suggest post #138 as a possible pursuit.
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Old 24th August 2018, 01:02 PM   #149
microx is offline microx  Spain
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Default It works!!

Using the internal oscillator I have 0.0012% at 1kHz. I need to go through every range etc but overall it works.

Many thanks to all who helped me esp BSST.
I don't know how I will fill my time now!
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