Power supply test points? Especially the +5.
Tom
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----- Original Message -----
From: sk_circuits@... [TekScopes]
To: TekScopes@...
Sent: Monday, December 15, 2014 1:43 AM
Subject: [TekScopes] tek 465 no sweep question
Hello to all the group members.
My tek 465 stopped working recently and I'm trying to find the offending circuit.
There is no horizontal trace on both channels on standard settings with auto triggering selected.
I can see a dot with beam finder button pushed but no trace.
In x-y mode the dot is visible and both x and y can be adjusted.
However both traces are visible (two solid lines) in 'chop' mode, but both disappear when I'm adjusting vertical position pots or any switch.
I don't have another scope to measure waveforms from the service manual so I followed the troubleshooting flow chart for the 'no trace' case and measured dc voltages on q1024 and u870 sweep logic chip.
q1024:
collector -0.2v (-1.7v in service manual)
emitter -4.6 OK
base -4v OK
u870 has incorrect voltages on some pins:
pin6 (auto rc) -0.3v (+5.2v in service manual)
pin17 (swp disable) -0.2v (+0.3 in manual)
pin19 (auto) 0v (+2.5v in manual)
All other pin voltages are in spec.
So now I'm stuck. Is it u870 fried or some other faulty component prevents it from working?
I could start desoldering transistors on the sweep/trigger board, but I don't fully grasp how the whole sweep circuit works so it would be a blind search.
Any help would be highly appreciated.
Thanks,
Serge.
