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Postby IK3HZI » Mon May 11, 2015 5:17 pm

Hello everyone,
I have a problem with the display, the number of hundreds of kHz does not turn on.
Everything else OK, regularly reads the frequency, as well as the manual selection of MHZ.
The display (VFD tube) works, even decoding uPB249.
I replaced the integrated Q9 and Q10 7475 7486.

Does anyone have some advice for me?
The integrated MSM580 should set the reading from 500, which are integrated? They are as spare parts?

Thanks in advance

Posts: 2
Joined: Sun May 10, 2015 6:30 pm

Re: YC601

Postby n4qms » Mon May 25, 2015 1:49 am

If I interpret the diagram correctly, each digit is selected by a pair of NPN transistors that connect to pin 3 of each digit.

For the 100 kHz digit, I would check Q21 and Q22 for a fault.

A 'scope will reveal if the select pulse for that digit is being fed into the base terminal of Q21 from Q5 pin 11. If this positive pulse is absent, Q5 may be bad.

One accurate measurement is worth a thousand expert opinions"
-- Admiral Grace Hopper
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Location: Louisville, KY

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