general-el: motorboating noise

Anybody experiencing motorboat noise during alignment proceeding on this Radio: GE 515F? Let me know what did you do to eliminate it.

Thanks:

Steve

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In most cases, motorboading occurs, if the electrolyt capacitors of the B+ voltage have lost their capacity. In this model this is a dual elyt C23A & C23B, both should have 50μF.

Try to solder an elyt of 47μF in parallel to C23A, and probably another in parallel to C23B. If motorboating stops, you were sure to replace C23A&B.

Good luck,

Dietmar

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Hi Dietmar,

I check both electrolyte (C23A, C23B) show 54.7uF, because I recap the whole system before I try to do alignment on it. Even I "cuered" the SMD (Silver Mica Desease) as you can see in the picture.

I do not see any other electrolyte cap in this Radio. If you have another tip it would highly appreciated.

Steve

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Hi Steve,

when recapping, often mistakes occur when the numbers on the capacitors were mis interpreted. One capacitor is critical in this sense, namely C20 (5nF). Please check its value. If C20 has to big a capacity, motorboading is very probable. This is also true for C17, which should have 2 nF.

Regards, Dietmar

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Regarding C17 and C20 they are together with C19 and C26 in one unit CERAMIC caps. I did not bother them (yet!) Now I just check C17 2.87 nF (should be 2 nF) C20 6.49 nF (instead of 5 nF)

Do you think they are too high in value and worthed to replacing? I think I do not have at Home ceramic caps in those value.

I want to tell you the whole story about motorboating: I followed the alignment chart, step one was ok, but when I want to do step two I get the motorboating when give the 455 kHz from my SG-8. 

Before I start alignment I can get two (only 2) local Station fairly clear with good volume without any motorboating noise. I hear this noise ONLY when I want to do alignment.

This will help to solve the motorboating noise?

Thanks:

Steve

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What you are describing looks like a feedback between the generator and the radio.  Please try to operate the radio via an isolating transformer.

Do you use a probe tip to inject the intermediate frequency? Else you may inject in the way shown in the graphics.

The ceramic capacitors look pretty o.k. Now I think, there will be no problem with them.

Regards, Dietmar

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Thank you very much for your illustration. I never put my wire loop in the cardboard, however this is a very clever idea. BTW mine loop (only in the Air without suppor by anything) is working well also.

Finally I finished the Alignment and I'm satisfied with it. Here you can see and hear (33 sec.)

Thanks again.

Steve

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