Re: Tek 4654M; No Trace, No +5V, No +95V; Help


Chuck Harris
 

There is no point on working on the 95V supply until you have
the 5V supply working properly, as 5V is used to drive the regulator
circuitry, and it looks as though if it is missing, it may shut the
HV oscillator down... preventing the +95V from being made.

-Chuck Harris



buma7@comcast.net wrote:

Have been concentrating on the +5V circuitry. Checked everything out left to right from Figure F0-10 R741 and R742 through U722B to Q742 and Q744. Tried to test everything in place but did lift a lead on some items to get a better reading and especially if the in circuit reading was off and/or was affected by other elements of the circuitry. The only things I found out of spec were Pin 6 of U722B read 0.660V Spec is +5.0V. Also the Pin 7 of U722A (32V circuitry) read 14.71V. Spec is 6.0V. The Q742, R746, R747 junction reading was -0.125V Spec is +4.9V. Not sure where to go from here. Considering pulling Q744 and Q746. 744 is on the A11 interface board. Problem is to pull it the legs are so short I can't test it with a transistor tester. 746 is the large transistors mounted on the back panel of the scope. I haven't done checking of the +5 unregulated circuit coming off of CR741. Am planning on picking up the circuit at R748 and C748 and try to check the components to the right on the schematic. Regardless, still struggling on this one to find a fault. Current plan was to try to solve the +5V issue before moving on to the +95V issue. I'd appreciate any advice and guidance on this one. Thank you. Stay safe and healthy. Harrison N1FAM



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