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Leader LBO-518 Scope W/ Y axis drift




 
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Author Topic: Leader LBO-518 Scope W/ Y axis drift  (Read 379 times)
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KA2PTE
KA2PTE
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« on: October 19, 2021, 08:05:00 PM »

Someone donated this to me a while back. The voltage / div controls were noisy and
the trace drifts randomly, so I cleaned up the wafer switches today and the controls are less noisy
but theres still drift on both channels.

The drift seems worse when you do the mag x10 pull on the knobs, eventually the trace floats
all the way off the top of the crt, usually when measuring something. If nothing is measured,
and its set to gnd, theres mostly negative drift, moreso if you tufn the knob to lower div settings.

I did just scrounge up the manual, any ideas on where to start looking?

* LBO-518.pdf (2272.91 KB - downloaded 37 times.)
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KA2PTE
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« Reply #1 on: October 20, 2021, 08:34:38 PM »

Someone linked me to this post:

https://www.electro-tech-online.com/threads/2n30809-dual-fet.104271/?highlight=#post851692

Apparently those FET's are a common problem, then he I guess isolated an issue with a Hybrid encapsulated IC
which is likely unobtanium.

When the scope is on a short time, the issue is not very prevalent, but seems the longer its on the
worse it is so it could be heat related.

2N3809 (Q23a/b) looks like a typo on the drawing (pg 38/39). Not sure if thats a dual FET....symbol looks wrong.
Guess I will have to eyball the board and see whats there.

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W1RKW
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« Reply #2 on: November 04, 2021, 07:15:37 AM »

Steve, 
Check your private messages.

Bob
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Bob
W1RKW
Home of GORT. A buddy of mine named the 813 rig GORT.
His fear was when I turned it on for the first time life on earth would come to a stand still.
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