Nakamichi Soundspace 3 no FM radio, bad diode?

[dplatt]

I bought a Soundspace 3 new back in 2003 and it's faithfully woken me up until recently because it's lost the ability to receive FM radio stations (AM, CD, AUX works fine).
When switched to FM, you can hear static normally but as soon as I hit a stereo broadcast the volume goes dead and I have to turn it up to max to barely hear the broadcast. I have basic diagnostic troubleshooting experience but I'm perplexed about diodes. I've found a bad diode (circled) It's wired in series, not parallel, with D109. D109 works like it should. D110 it lets current through both ways. Does anyone know the identity of this diode. My initial inspection also found a bad capacitor. Not sure if that's electrolyte or glue at the base but it displayed a steady resistance when checked-didn't increase to OL and had a slightly bulged top. So I have a new one on order. But any info on that diode would be great!

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

That is Zener Diode, did you test it off the board?

[dplatt]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

did you test it off the board?

Thanks for the reply, I haven't pulled yet but am planning to soon. It appears that it's wired in series with the other one and there are no connections between them so I am assuming there should be only current flowing one way like the other one. Unfortunately, I don't have the datasheet so I don't have a part number. If it's bad there's really no easy way to figure out the voltage and I'll have to the do it the hard way with a power supply, resistor, and multimeter, correct?

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

Just have to find out for sure first if it is bad out off the circuit. Another thing on the board is the yellow glue (turning dark brown) on the component, it is corrosive and also conductive so it must be removed.
Pictures of the whole top and bottom side of the board?

[dplatt]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

There are three units: the main, companion, and subwoofer. Behavior isn't altered with/out the subwoofer attached-so not pictured. Order of attached pictures are main top; main bottom; companion top; companion bottom (all pictures are maximum size 1333x2000 (click to enlarge)

As an interesting aside, the capacitor change didn't do anything to fix the radio-but it does now retain the time if the power is lost (previously would have to reset clock after power failure) and it doesn't make crackling sounds when the volume is turned up and down-don't you just love fixing things other than what you set out to fix...

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

The pictures are mirror images hard to read the part's designators, P/N of the IC 102? it looks like AM/FM IF DETECTOR IC.
LA1833??
http://pdf1.alldatasheet.com/datashe...O/LA1833N.html

You check the Voltages and the L & R output of the IC.

[ben7]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

Based on the graphic under diode D110, it looks like it is a zener diode. Zener diodes are meant to conduct both ways, however one way is like a normal diode and the other is with a certain voltage drop (ex: 5.1v, 16v, 13.6v......)

It might be the radio receiver IC that is bad.

PS I mirrored the image for you:

[dplatt]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

Sorry I thought that mirroring would make it easier to id the top components on the bottom of the board. Anyway, voltages from the L & R output of the IC (pins 13 and 14): 48mV (supposed to be 1.8V according to the data sheet) and have a resistance of 6.64 k ohms (supposed to be 3.3 k ohms according to the data sheet).

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

What DC voltage do you get at the VCC pin?

[dplatt]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

What DC voltage do you get at the VCC pin?

I'm assuming that's between pins 9 and 5 (GND)- never tested an IC before: it's 5 volts... which looks like it's within spec. So a bad IC then?

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

OK, that is OK.

[dplatt]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

Hmm... where do I go next? I checked the film capacitors and I found one circled that was supposed to read 220 nF but measured ~193 nF. The others were ~1 nF around their expected values. There is no letter code on it-indicating tolerance as I understand it…

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

That is OK, it should have letter after the value, J = 5%, K = 10%.
You will need the scope to look at the audio output signals from the IC to see if the level is low.

[dplatt]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

Is there any way to perform an equivalent of this test without a scope-the only tool I have at the moment is DMM

[budm]

Re: Nakamichi Soundspace 3 no FM radio, bad diode?

Audio signal tracer using PC powered speakers with 1K resistor, 0.1 uf cap.