Marantz 2235B Tuner Issue???

[mikejennens]

I have a 2235B and everything works fine except the tuner. It picks up a few stations, but misses many (We have less than a dozen FM stations from which to choose).
-I know I can get stations; I do on other receivers.
-The stations that do come in are very weak; I have to turn up the volume quite a bit to hear them.
-The tuning meter, signal strength meter, and the stereo light never budge, even when I manage to pull in a station.
-When I do have a station pulled in and I push the FM Dolby 25us button, the station gets muted to the point I can't hear it.
-The FM muting button has no effect; I don't hear the usual "rushing" sound with FM muting not selected.
-I get no AM reception at all.
-I have de-ox'ed and faderlubed all my switches more than once.

Any input on what the issue might be? I don't have an o'scope, so if it's an alignment issue, I'll have to either take it to someone or live with it.

Thanks in advance for any suggestions or input.
Mike

 

[Conrad Hoffman]

I don't know how integrated the tuner circuits are, but it could be a bad transistor that kills the gain, a bad coupling cap, a cracked trace (signal still gets across the capacitance of the bread, or about fifty other things. Without a scope and a schematic I wouldn't know where to start. That's the only good way to troubleshoot this. Whatever you do, don't go turning any of the alignment adjustments!

 

[infinia]

-I get no AM reception at all.

This might be the key somes they share common circuits. but sounds like the RF or IF tuned circuits have drifted off a bit.

 

[east electronics]

a 2235 unit

is probably 25-30 years old ..... similar units like 2245 and more come in to my shop for repiar or upgrade

none of the existing electrolytics inside was even close to the original value ...

you may recap the all unit but simply do not touch any trimmer especially in the tuner area

this will make everything back to normal

 

[infinia]

Yes the AGC detector is usually common to both AM and FM, look there first, could be a leaky small bypass electo. If it is loss of gain due to drifted tuning, then you would most likely hear distorted audio.

sakis. I like your trouble shooting style, works best without schematic or equipment

 

[east electronics]

we meet infinia

yet again on a repair issue

but it seems that we might share the same feelings about greek wine but not about repairs

i wasnt talking about "a" capacitor ....i was talking about ALL capacitors ...

22XX family i repaired i think 4 pcs this year none of them had a proper electrolytic inside

only one of them that i repaired i replace all of them inside and since tuner seemed to work properly i left all electros there as was ...

costumer takes the amp very happy with it ....operate it for a month and then return it with the problem of 1KHZ sound to all inputs ....

the electros i didnt change in the tuner area produced some oscilation that was audible in the all amp ....replaced them to and all is fine ...

 

[infinia]

-The stations that do come in are very weak; I have to turn up the volume quite a bit to hear them.
-The tuning meter, signal strength meter, and the stereo light never budge, even when I manage to pull in a station.

OK Sounds like the AGC detector. ( but it is part of a control loop )


sakis here we call that shotgun trouble-shooting

 

[mikejennens]

Thanks for all the input.

How do I identify the AGC detector?

I have done some recapping, but not on the tuner section.

Thanks,
Mike

 

[infinia]

Really need a schematic or picture
What mods or repairs have you made so far.

 

[mikejennens]

Infinia,
I recapped and replaced the diodes and transistors on the PS board.
Mike

 

[infinia]

The AGC detector is the last part of the AM tuner (usually part of an IC) also functions as AM demodulator besides FM AGC det. But that detector control output goes everywhere so you might trace it out on the schematic and use your DMM to check the voltage as you tune across a strong station.

I'm not sure what skill level you are at, but you could take sakis approach and recap around that IF/AGC IC when you locate it.

 

[mikejennens]

Infinia,
Thanks. I found the service manual so I'll look through it and see what I can find.
Mike