I'm restoring a Harmon Kardon HK560 receiver, and all now works EXCEPT the AM tuner section. I can amplify an untuned AM band signal from the antenna, but no tuneable signal. FM reception and tuning works normally.

I've located the AM IF filter, which is identified in schematic as 445CL. The plastic case is partially melted, so no external markings can be read. It is a small PCB-mount 3-pin chip that looks physically similar to a Murata SFU455.

I can't find a source for this Murata chip anywhere online, though I have a spec sheet for it. Can anybody recommend a source for this or compatible filter?

The nearest functional equivalent I have found is an unbranded 5-pin ceramic 455kHz AM filter from Wagner Electronics in Sydney. The catalogue includes a rudimentary pinout that I don't understand. My guess is that selection among the three available ground pins determines voltage at the output pin.

I'm sending a clip image from the catalogue - hope it gets uploaded.

Any advice on sourcing a direct replacement filter, or adapting the available filter from Wagner, would be greatly appreciated.

Maven [back from a few years of other distractions]

hope it gets uploaded

It is.

I can't find a source for this Murata chip anywhere online

FWIW: https://latinafy.com/products/sfu-455-a-murata-ceramic-filter-made-in-japan/

Thanks GTC for the reference. The price, including FedEx shipping (no alternative) comes to around A$93!

This makes me more keen on repurposing the item available from Wagner locally, if that is feasible.

Maven

Hi Maven

All you need are the input and output pins. Ground everything else.
The numbers refer to the pin spacing in mm.

10kHz bandwidth, eh? Should sound good for AM.

In an emergency you can bridge the input to output with a small ceramic capacitor, ignoring the earth terminals.

You could try it, just to make sure it was the filter that caused the problem.

Robbert - for your suggested test, a few questions from a late learner...

1. Do you mean bridging between the Input and Output PCB pins for the IF filter with a capacitor alone, or capacitor in parallel with the proposed new filter, prior to soldering?
2. I have a random assortment of small caps. What sort of values should I use for this test?
3. What kind of signal output should I be looking for during this test?

Thanks for advice
Maven

1. With the capacitor alone - solder it in.

2. It's so long since I've done this, I can't remember if I used 100pf or 0.01μF - I guess there's a wide range. After all, you only want to hear some audio, for the test you don't need the right level.

3.As above - it's only a test, you just want to hear something.