HK 330C - Dead FM

A Sound Mind

Reckless Tinkerer
Hi All,
I get no FM output either in mono or stereo mode. I tracked the signal on the tuner board to the BA1310 multiplexer IC. Pins 4 and 5 should have an output signal, but do not. I tested all the transistors and diodes in this area and they're fine. I don't fully understand the FM multiplexing circuit and don't want to replace this $10 IC if it isn't necessary. Also, the stereo indicator doesn't light. AM/phono/aux all work fine. Does anyone know of a common cause of FM failure with this model? Can someone help me to zero in on the source?
 
check for FM at pin 2 of that IC. I have seen them fail and not provide FM stereo lite, and can fail totally. If you don't have a signal on pin 2 the IC is probably good, and you problem is earlier like in IF section. Trace back looking at both sides of the C402 cap (4.7uf). I signal on one side of the cap it it probsably bad. And troubleshoot with the muting off to see if you have any signal along the dial. (I assume you are using a signal tracer to check for sound.)
 
Thanks Tom - Pin 2 is dead. Tracing the signal from the origin, there's nothing coming out of pins 3 and 5 of IC202 (BA401). There is signal at the collector of Q204 up thru pins 8 and 9 of IC301 (BA1310). Why do I see a signal on the collector of Q204 and nothing coming out of IC202?
(This model has no muting control)
 
I had the same issue on a 330C and dropping a BA1310 from a 330B worked like a charm. I've since bought two spares IC from eBay and only paid $10 for the pair. A little research told me these were all equivalent, if that helps: ba1310, ba1310f, lm1310, lm1310n
 
If you decide you do need one and want one of mine, I'm happy to send it to you USPS.
 
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