Alpine CDA-7840 low volume

[junktv]

Hi guys. I was hoping someone here may be able to help me out. This older Alpine CDA-7840 I have started acting like it was almost muted a while back so I pulled it and got a new one. Well I found it in the back of the closet and figured I'd give it a try again.

When I say almost muted I mean both speaker out puts and rca are barely audible cranked all the way up. When it first started this it was somewhat intermittent then got worse to where it is quiet all the time.

I can't visually see anything wrong other than it had a little white oxidation near the face plate header which in he pics is on the bottom edge in both. I've double check that the cell mute and button mute are off. What would be the likely failure here?

[DJduck]

Re: Alpine CDA-7840 low volume

Check how the signal is on the output IC's input legs. If it's normal, your problem is likely the chip, if it's too low, your problem is the pre-amplifier.
That's the first thing I check on car stereos

[junktv]

Re: Alpine CDA-7840 low volume

I'm a noob at this and not sure what is what other than being able to identify if it's a IC, diode, resistor , chip or cap. Would you mind telling me which IC's to check? If I remember correctly I'm thinking I can then find a spec sheet for the IC to figure out what legs to check and what voltage it should be.

Sound quality is great just really low volume through wired or rca.

[budm]

Re: Alpine CDA-7840 low volume

"When I say almost muted I mean both speaker out puts and rca are barely audible cranked all the way up" Since the Line level RCA outputs are also low, then I would suspect something in the preamp section or audio processing circuit control circuit which will be common to both channel. There are so many ICs on the board, you will need to get the P/N as printed on top of the ICs and start looking for spec sheet of the ICs to get the pin out to at least check the DC power supply voltages feeding the ICs first, then use the oscilloscope to look at where the signals drops out in level. Circuit diagrams will be a big help for sure. The cause of the problem has to be something common to both channels.

[junktv]

Re: Alpine CDA-7840 low volume

For tools I have a cheap DMT7 digital multimeter. No luck finding a service manual by alpine model # or board number 84D20428Y01(the 6Y is a possible 6 or 9Y).

Can You ID the pre-amp section for me so I know which ones to look at?

[budm]

Re: Alpine CDA-7840 low volume

It has lots of OP-AMP ICs 4560, and Sound Fader control TEA6320. All you can do is the voltage check but you will not be able to do much without the scope or audio signal tracer.

[junktv]

Re: Alpine CDA-7840 low volume

Got the 4560's checked and they all read the same. The values are in the pic. I noticed when I checked IC260 on the board pin 2 and 6 would get a static like a loose wire. From 1-35 the static was just as loud as if it was turned all the way up but none when on 0. Pin 6 was the right front speaker and pin 2 was the left front. No speakers on the rear.

Wanted to add that the voltages stayed the same no matter what volume or if muted.

[junktv]

Re: Alpine CDA-7840 low volume

I don't think I have the tooling or knowledge to continue. To the parts bin it goes.