Something new...to me at least.

oldskool69 · Jan 13, 2010

Got a Sony CFD-5 from a thrifty on December 29. :thumbsup:

I got the deck going again which is great but I could not get volume out of the right channel. I know the signal is good from the tuner, line in, etc. Well,I pulled the PCB and noticed what appeerd to be a creeping black corrosion, almost like a mold got under the etching. Has anyone seen this before? :huh:

I am prepared to rework the PCB if ultimately that is it, but am curious about this phenomenon...

Superduper · Jan 13, 2010

I've seen corrosion of all sorts but haven't seen what you are describing. The etching is actually just a copper foil that is "glued" onto the board. Perhaps some chemical that is corrosive to the adhesive got on there and is slowly eating the glue.

Fatdog · Jan 14, 2010

That does sound kind of freaky. :hmmm:

Almost like a horror movie for boomboxes. :-D

Can you post a pic?

oldskool69 · Jan 14, 2010

Fatdog said:
That does sound kind of freaky. Almost like a horror movie for boomboxes.

Can you post a pic?

Will do this evening when I get home... :-)

oldskool69 · Jan 14, 2010

Well...apparently this poor thing was subject to moisture... :-/

As stated before, you know the signal is there, you can hear the left channel fine, the right channel faintly with the volume all the way up... :-/

Volume, tuner wheel, and EQ Board:

Mainboard: (Follow from left go down and to right...)

"Sigh..."

Fatdog · Jan 14, 2010

Is there a clean point to bridge it? :huh:

oldskool69 · Jan 14, 2010

Fatdog said:
Is there a clean point to bridge it?

Stopped working on it tonight, will resume tommorow. If need be I will retrace the circuits. Hopefully it will not need more parts... :-/

Superduper · Jan 14, 2010

Most modern circuit boards are conformal coated after assembly and before installation. This makes it hard and next to impossible to check for continuity between solder pads. Reflowing the solder pads prior to checking with DMM will make the process more palatable. When done, I recommend recoating the board to protect and improve the board's weather resistance.

If you can't find any obvious bad spots with a DMM, then use a circuit tracer to determine where the signal attenuation begins, but then you probably already know that. :-)

oldskool69 · Jan 15, 2010

Superduper said:
...Reflowing the solder pads prior to checking with DMM will make the process more palatable. When done, I recommend recoating the board to protect and improve the board's weather resistance...

That actually is what I started doing. I actually used a superfine sandpaper to remove the coating/corrosion and expose the traces. I found out, much to my dissapointment, the copper had been compromised. Once I finish removing the corrosion, I will wash the board with electronics circuit cleaner/deoxidizer, will retrace the circuits, check continuity and go from there. If all is well, I will recoat the board and move on. Hopefully no board components were damaged... :hmmm:

eldorado · Jan 15, 2010

doesnt seem very hard to do...

just clean it well with alcohol ,

not whisky,

of course,

:-D

and if that area is related to audio , you may have found the problem

try some fixing with solder... on those broken places, maybe if its too extense, with some wire.

monchito · Jan 15, 2010

i have seen that and battery acid ruined boards too :yes:

oldskool69 · Jan 15, 2010

I PM'd Sin to see if he still had the service manual for th CFD-5... :-)

oldskool69 · Jan 16, 2010

Update....

Left and Right channel amp OK! :thumbsup:

Left channel functional throughput is fine.

Moving onto line level throughput at the right channel...issue is somehwere in the pre-amp? :hmmm:

Fatdog · Jan 16, 2010

So far, so good. I hope it's nothing serious. :yes:

oldskool69 · Jan 16, 2010

Fatdog said:
So far, so good. I hope it's nothing serious.

Well, the EQ and volme control board checked out OK. :thumbsup:

So now onto th mainboard and pre-amp. The selector switch was crusty as well so it may ultimately be the culprit, we'll see...

The corrosion made for a heck of a mess to the circuit functionality :thumbsdown:

, and the more I looked, the more I cleaned... :-/

Superduper · Jan 16, 2010

Sounds like you are making good progress. I would never use abrasives to clean off the conformal coating, especially when the copper condition might already be suspect -- they make chemicals (conformal coating removers) that will make quick work of it but it's not something most people keep in their tool chests so I guess use what you have.

oldskool69 · Jan 16, 2010

Superduper said:
Sounds like you are making good progress. I would never use abrasives to clean off the conformal coating, especially when the copper condition might already be suspect -- they make chemicals (conformal coating removers) that will make quick work of it but it's not something most people keep in their tool chests so I guess use what you have.

I agree with you about the abrasives...the abrasive I used is more of a wet finishing polish sandpaper with a very gentle touch. :yes:

And you're right, the coating remover is not exactly something I had lying around so I went old school like my dad taught me years ago. :lol:

(He's been in the elctronics repair business for 45+ years. :-D

)

Looks like I'm going to hit the wall unless I get a service manual to tell me what values I should be seeing from pre-amp to amp...or I'm just getting tired. :lol:

Superduper · Jan 16, 2010

You've got one good side. Using a circuit tracer, you should be able to compare signal levels from identical places L/R and the location where attentuation is discovered will be the problem area. I know, I know, it's sound easy but in reality, is easier said than done .... :lol:

oldskool69 · Jan 16, 2010

Superduper said:
You've got one good side. Using a circuit tracer, you should be able to compare signal levels from identical places L/R and the location where attentuation is discovered will be the problem area. I know, I know, it's sound easy but in reality, is easier said than done ....

Oh I know, that's exactly what I'll be doing tommorow...just tired...which is making me lazy. :lol:

Thus wanting the service manual so I can say...play a little less Carmen Sandiego/Where's Waldo tracing the circuit. :lol:

Superduper · Jan 17, 2010

oldskool69 said:
Superduper said:

You've got one good side. Using a circuit tracer, you should be able to compare signal levels from identical places L/R and the location where attentuation is discovered will be the problem area. I know, I know, it's sound easy but in reality, is easier said than done ....

Click to expand...

Oh I know, that's exactly what I'll be doing tommorow...just tired...which is making me lazy.

Thus wanting the service manual so I can say...play a little less Carmen Sandiego/Where's Waldo tracing the circuit.

Sin didn't get you the schematic? I know he has the SM, he told me so yesterday so unless it vanished between now and then, he should have it.

Something new...to me at least.

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