How can I identify and fix a capacitor issue on my Kenwood A/V receiver?

[JoshB.]

Hello everyone!

I need help identifying a capacitor. It reads 12.C29 Its very small, maybe .25" long.
It's on an audio input board from my Kenwood A/V receiver. Thanks for the help!
Josh

 

[Bystander]

https://www.google.com/search?q=tan...pedia.org%2Fwiki%2FTantalum_capacitor;960;556

 

[berkeman]

Hello everyone!

I need help identifying a capacitor. It reads 12.C29 Its very small, maybe .25" long.
It's on an audio input board from my Kenwood A/V receiver.Thanks for the help!
Josh

Looks more like a cylindrical package crystal from that angle...

 

[davenn]

Looks more like a cylindrical package crystal from that angle...

Totally agree Mike. definitely, no doubts, a crystal OP reread it ... its 12.2x29 the x may be a 0 (zero)
12.2 MHz or possible 12.2 kHz

to the OP
I can see a Hz printed on the PCB just to the right of that brown electro capacitor what comes before that ( hidden from view by the cap) ??

Dave

 

[JoshB.]

WOW - You guys are good.

Dave - It says 12.288MHz

Any Idea on where I can a replacement?

EDIT - Just found a pack of 10 on Ebay for a few dollars.. worried about quality though.

 

[berkeman]

Check Digikey and use their part sorting feature to look for cylindrical crystals.

Although, as long as it fits in that area of the PCB, you could use a traditionally packaged crystal instead (still through-hole leads).

 

[berkeman]

12.2x29 the x may be a 0 (zero)

Dave - It says 12.288MHz

BTW, those two numbers are far enough apart that using the wrong frequency could affect circuit operation, especially in a radio receiver. I'd go with the frequency on the part. Do you have any idea why the frequency on the part differs from the silkscreen number on the PCB?

 

[JoshB.]

BTW, those two numbers are far enough apart that using the wrong frequency could affect circuit operation, especially in a radio receiver. I'd go with the frequency on the part. Do you have any idea why the frequency on the part differs from the silkscreen number on the PCB?

Maybe they rounded the .288 to .29?

 

[davenn]

its most likely to be the clock oscillator crystal for that large micro chip to the right of the crystal
I would hesitantly guess ( in this situation) that several 10's of kHz probably won't make too much differenceDave

 

[JoshB.]

its most likely to be the clock oscillator crystal for that large micro chip to the right of the crystal
I would hesitantly guess ( in this situation) that several 10's of kHz probably won't make too much differenceDave

How can I find its load capacitance? I'm guessing 16pf.

You've all been very helpful, I thank you!

 

[davenn]

you would need the service manual or detailed schematic of that part of the board
parts list and/or schematic would have that info

 

[berkeman]

How can I find its load capacitance? I'm guessing 16pf.

That's a good ballpark guess for the crystal spec -- at that frequency 16-18pF is very common. Can you see any explicit caps on the PCB on the crystal nets? The total capacitance seen by the crystal oscillator circuit would be the two PCB caps in series (so half of their value) in parallel with whatever the input capacitance of the oscillator is.

 

[JoshB.]

I really can't tell what the caps are - I am still very new to circuitry.

What would happen if I placed an incorrect crystal on this board?

 

[berkeman]

I really can't tell what the caps are - I am still very new to circuitry.

What would happen if I placed an incorrect crystal on this board?

Hard to tell. What is the microcontroller (uC) chip to the right? Can you read a part number off of it? If so, the datasheet for that part may specify a particular crystal capacitance value, and recommend the corresponding PCB capacitors to get to that overall parallel resonant capacitance value.

 

[JoshB.]

Well, the two caps next to the crystal say 10v100uf - as for the chip "Analog Devices ADSST-MEL322 173068.1-0.2 0240"

 

[berkeman]

No, those are big electrolytic capacitors for the voltage rails. The caps I'm referring to would be small SMT capacitors, one from each leg of the crystal to ground.

 

[JoshB.]

The SMT's are so small, there is nothing printed. I tried to get a picture, but my phone has no macro setting so close up photos are blurry. I'm going to hunt for the manual, but I doubt I'll find it.

 

[berkeman]

The SMT's are so small, there is nothing printed. I tried to get a picture, but my phone has no macro setting so close up photos are blurry. I'm going to hunt for the manual, but I doubt I'll find it.

You would need an LCR tester, or a "capacitance" test range on your DMM to measure the caps. They would likely be in the 30pF range.

Just start with 18pF or so for the first crystals you buy. That should be pretty close.

 

[Baluncore]

Why fix the crystal if it ain't broke? The brown stuff looks like glue to hold it in place.

 

[davenn]

Why fix the crystal if it ain't broke? The brown stuff looks like glue to hold it in place.

well he thought it was a capacitor initially

but it still begs the Q you asked ...

JoshB ... why do you want to replace the crystal ? it doesn't look damaged
This thread so so far offtrack because of things not being established in the original post

I think you need to start over and tell us all why you are delving into this receiver audio board unit and what is its fault / symptoms ?

Dave

 

[JoshB.]

OK - I thought it was damaged and the brown stuff looks to be coming out of the crystal which I thought was a cap. (I'm very new to circuitry and components)

So I've had this A/V receiver (VR-7070) for many years - then suddenly a very loud high pitched whine would come from all speakers. So I assumed it blew a cap somewhere. When I dug into it, this crystal is all I could find with visible damage ( or so I thought).

You guys really know your stuff - and I appreciate your help.

Anyone know what I should look for? Or how I should approach fixing this?

Josh

 

[Wes Tausend]

Josh,

The high pitched whine usually means some sort of feed-back has developed. The most likely cause will be a electrolytic capacitor to ground, that has failed, and now does not decouple a hf audio ac signal (aka feed-back whine) on a dc feed-back bias voltage line. The good news is the circuit is obviously still ampilfying, although strong feed-back can soon overheat delicate parts.

It really would help to come up with a schematic since they often show a common feed-back circuit derived from the heavy duty output stages. But finding the factory pin read-out and specs, from the IC audio pre-amp chip may be just as good. Look for a pin that requires dc bias voltage and then replace the electrolytic capacitor that is supposed to decouple hf audio. Electrolytic caps are the most likely failure of aging equipment, so you were likely on the right logic track and do suffer from parts non-recognition just like you also suspected. The electrolytics are in cans, and have a plastic sleeve over them. I can see two with black plastic sleeves near the bottom of your photo for instance. The light stripe usually designates the voltage polarity. They are usuallly large enough that the volt and capacitance ratings can be easily read to facilitate replacement. Sometimes the sleeve is blue instead of black.

If you are ambitious, you could replace all the electrolytic caps on the board with new, or known good used items.

Wes
...

 

[sophiecentaur]

well he thought it was a capacitor initially

but it still begs the Q you asked ...

JoshB ... why do you want to replace the crystal ? it doesn't look damaged
This thread so so far offtrack because of things not being established in the original post

I think you need to start over and tell us all why you are delving into this receiver audio board unit and what is its fault / symptoms ?

Dave

And you wouldn't have the wherewithall to test it in any case. It will measure as an open circuit / very small capacitor. I guess if it had the damp in it, you may measure some conductance.
PS did you ever see a 12kHz crystal? http://www.ebay.co.uk/itm/12-kHz-Vintage-Quartz-Crystal-Oscillator-QTY-1-/261476500409 This eBay link may not last long. :)

 

[JoshB.]

Hey guys - I've managed to find the service manual, but if I could read it as intended I would be in a higher pay bracket...

Manual

If it helps, all I hear is the feedback - not the audio source. And would a bad cap show signs of damage in this case?
Too bad I'm in school for Mechanical engineering and not electrical...

Thanks again guys - this is a great forum!

Josh

 

[davenn]

Hi Josh

unfortunately I don't really want to signup to a site just to download the file so I can read it
I suspect others will probably feel the same way

wonder if you can pick another site, thanks ? :)

 

[JoshB.]

oh sorry - didnt know you had to signup for it.
Anyone know of a good free hosting site?

 

[Wes Tausend]

oh sorry - didnt know you had to signup for it.
Anyone know of a good free hosting site?

Josh,

The 32 page pdf manual did download, without sign-up, on my miserable atom-powered 10" netbook with Explorer 8, but I can't magnify it enough to read it decently without crashing. The site did complain about my ancient browser but I am not sure my meager chipset can handle any more data from a newer version. And I don't trust microsoft to let me back out without re-installing my op sys..

I think I did see a set of output IC's (IC123's 1, 2) fed by a single IC pre-amp (IC12). They terminate FR and FL which seems to indicate a stero output section for front right, left. From there a feedback path is fed back to IC12 pins 5 and 25, but I don't see a decoupling capacitor on these.

Another detrimental feedback path is sometimes inadvertently established by a power feed where the current draw of an output stage overloads the stability of a normally steady dc supply and this wavering cycle is fed back to the power supply feed of an earlier amplifier stage. There again a local filtering capacitor to ground from the supply line may have failed, but this is also true of the main supply in some cases. In any case, a leaky power transistor may also draw too much current for the voltage divider circuit design to filter smoothly. Discreet transistors are not used much anymore, except for outputs. I thought IC's 123 might each be a black-box push-pull set combo.

Does your feedback whine travel through all audio channels equally? I'm imagining you don't have a lot of test equipment to work with. You might be able to measure (or hear) a higher audio ac voltage on one channel more than the others with an ordinary multimeter. If so, it might be possible to isolate a single channel as the source of unwanted feedback generation. Don't know what else to tell you.

I need an updated computer. Even the new PF forum software no longer renders correctly, making posting a chore. The above drop-down tabs often get stuck on my screen and, after saving a prospective post to clipboard, I must laborously reload the page to get rid of them.

Good luck.

Wes
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