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When DeOxIt doesn't do it . . .

Macaroon

Macaroon

Active Member
I recently got a 2238B from eBay which was advertised as having a scratchy volume control. I've bought 7 or 8 receivers in the past year or so, most of which had scratchy pots and were priced accordingly ( I usually buy the lower-priced stuff due to my chronic brokeness). When they show up I pull out the Caig's and get to squirting—and almost always have successful results right away. I think my luck has run out.

This time, the volume and balance pots were in need, and after the first treatment the balance responded nicely. The volume . . . not so good. I've given it, probably, 10 good doses of DeOxIt over the past week, turning the knob a couple hundred times after each one. Still, it's scratchy. Actually, it's scratchy in the left channel and cuts out in the right. And more weirdness: if I let it play for an hour or so, it seems to get better. Much less scratch and very little cutting out.

It has other symptoms, too. The right channel might be a bit weaker than the left, and there's a buzz in both (like a bad-ground 60-cycle thing, but not too loud). Finally, tonight the single working dial lamp was pulsing, seemingly in sync with the channel cutting out. It's alive!!

Does it sound like this guy needs major surgery? And light you can shed is much appreciated.
 
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Confession: my eletronics repair prowess at present is limited to applying DeOxit and replacing lamps. But I'll check the joints out. Are bad ones visible to the naked eye?
 
Macaroon said:
Confession: my eletronics repair prowess at present is limited to applying DeOxit and replacing lamps. But I'll check the joints out. Are bad ones visible to the naked eye?
Click to expand...
Hi Macaroon,
To my naked eyes, no they aren't, unfortunately. I use a lens to check bad solder joints, but otherwise you can just wiggle the potentiometer body slightly.

Given the other symptoms I would say your receiver needs a little more attention than a few sprays of De-Oxit.

Since the 2238B is a great "small" Marantz I would suggest taking it to a reliable electronics repair shop for an overhaul, I think it's more than worth spending a little to keep it in perfect shape.
 
Check which version of DeOxIt you're using, 100% or 5%. The 5% can actually harm certain types of potentiometers that have carbon contact surfaces.
Caig Tech Support said:
"Normal" carbon surfaces will not be adversely affected by the D5 spray, however, you are working with vintage equipment, and it’s highly probable that the already fragile or mechanically weak pots will sustain damage after exposure to solvent, causing the removal of carbon.
Click to expand...

Good thread HERE, follow the links in the posts to more info.
 
Gigapod said:
Hi Macaroon,
To my naked eyes, no they aren't, unfortunately. I use a lens to check bad solder joints, but otherwise you can just wiggle the potentiometer body slightly.

Given the other symptoms I would say your receiver needs a little more attention than a few sprays of De-Oxit.

Since the 2238B is a great "small" Marantz I would suggest taking it to a reliable electronics repair shop for an overhaul, I think it's more than worth spending a little to keep it in perfect shape.
Click to expand...

I wiggled the pot body, and there was no effect. In fact, it didn't really wiggle; it's quite firm. If the solder joints are the little nibs on the green side of the pc board, one looks like it might have a tiny spot of rust, but that's it. I'm afraid you're right about the need for an overhaul. Thanks for the info.
 
ozmoid said:
Check which version of DeOxIt you're using, 100% or 5%. The 5% can actually harm certain types of potentiometers that have carbon contact surfaces.
Click to expand...

I thought it was the 100% that ate carbon for breakfast. Oops. I've fed this volume pot a varied diet of D5, Gold, and Faderlube, all with pretty much the same effect (none). Thanks for linking me to the other thread. Good guidelines for caution.
 
Hi Macaroon,
Do you get a scratchy sound/cuts only when turning the volume up/down, or all the time?
I had exactly the same problem in my 2238BL and finally traced it down to a faulty transistor in the tone control/preamp circuit.
The hum/buzz also seems to indicate a problem with the power supply, and so does the pulsing dial lamp.
These are simple problems to solve for an experienced technician with the proper service manual, so I really suggest you find a honest one in your area.
I don't know how far you are from Fred Longworth's shop but it may be a good idea to check with him.
 
Macaroon,

The important clue here is that after the machine has been playing for an hour or so, the symptoms are much reduced.

Potentiometers don't heal themselves that way. I suspect either transistors or capacitors in the preamp section -- and I'd place my wager on the caps.

If you want to proceed on your own, get service literature on your machine, and consider replacing the population of electrolytic capacitors on the preamp circuit boards.

* * * * *

Also, I would pull the bottom off your Marantz, and take a close look at the preamp circuit boards that the frontpanel controls and switches attach to. Does it look like someone has pulled the frontpanel and taken these boards loose? Do the wires to the boards have a "disorganized" look? Do you see a pinched wire? Can you find a terminal on one of these boards with fresh solder on it, suggesting a wire may have come loose and had to be resoldered?

Best,

Fred Longworth
 
Gigapod said:
Hi Macaroon,
Do you get a scratchy sound/cuts only when turning the volume up/down, or all the time?
I had exactly the same problem in my 2238BL and finally traced it down to a faulty transistor in the tone control/preamp circuit.
The hum/buzz also seems to indicate a problem with the power supply, and so does the pulsing dial lamp.
These are simple problems to solve for an experienced technician with the proper service manual, so I really suggest you find a honest one in your area.
I don't know how far you are from Fred Longworth's shop but it may be a good idea to check with him.
Click to expand...

Hi Gigapod,

The scratchy sound (left channel) is pretty much only when turning the volume knob. When first powered on, it makes noise from the start position (about 7 o'clock), to about 10 o'clock. After warm-up it seems to be just a little scritch that ends before the 8 o'clock position. The cut-out (right channel) happens in the same positions at power on AND continues cutting out by itself until it's warmed up. The buzz is always there, unaffected by volume.

I'm glad to hear that the problems are simple for a tech, even though they're far beyond my expertise. I wonder if any of the local electronics shops take Blue Shield.

Thanks a lot for the input.
 
I agree with what they said--the volume pot is probably not the problem. There is pprobabbly a loose soder joint or a bad xistor or cap somewhere.

Regardsm
 
Fred Longworth said:
Macaroon,

The important clue here is that after the machine has been playing for an hour or so, the symptoms are much reduced.

Potentiometers don't heal themselves that way. I suspect either transistors or capacitors in the preamp section -- and I'd place my wager on the caps.

If you want to proceed on your own, get service literature on your machine, and consider replacing the population of electrolytic capacitors on the preamp circuit boards.

* * * * *

Also, I would pull the bottom off your Marantz, and take a close look at the preamp circuit boards that the frontpanel controls and switches attach to. Does it look like someone has pulled the frontpanel and taken these boards loose? Do the wires to the boards have a "disorganized" look? Do you see a pinched wire? Can you find a terminal on one of these boards with fresh solder on it, suggesting a wire may have come loose and had to be resoldered?

Best,

Fred Longworth
Click to expand...

Thanks for the guidance, Fred,

Though I hope to expand my abilities in receiver repair in the near future, right now replacing the caps on the circuit board is in the same realm as rebuilding a tranmission or performing a kidney transplant. All three would end tragically. Best I leave it to the pros.

I'm not home today, so I can't check the receiver underneath, but as I recall, everything looked clean, organized, and unmolested. So clean, in fact, that I'm not sure I could tell a fresh solder from an old one. (I've been gazing at the area quite a bit; the bottom cover's been off most of the time I've owned it.) The view under the top cover is a different story: quite a bit of soil across the landscape.

I'll be back home tomorrow night and look more closely at the areas you mention.
 
Bad caps and solder

your problem may be worn out pot. The oxidation acts like an abrasive and after time will wear the contact surfaces in the pot. You can sometimes find a replacement pot on ebay or I can research one for you. Also, I have used Rat Shack's Control/contact CLeaner & Lubricant spray with good results on dirty pots. Be sure to clean the switches as well. Make sure that your cleaner is getting into the pot itself.
The other problem you are having (hum) is due to bad capacitors in the power supply. Look for bloated caps or ones that have leaked. Also look for any heat discoloration on the board. That is a sign of bad connection due to poor solder. Get a magnifier and look at the solder connections. Remove and resolder ones that look bad or questionable.
Good luck
~RB
 
I've taken the coward's way out for the time being, and resigned myself to letting the 2238b warm up for an hour before I play it. I took a look underneath and didn't see anything too alarming, but just in case I'm missing something I took some pictures and attached 'em. The only thing that looks unusual to my very UNtrained eye is in the picture labelled BlueThing; it looks like some type of capacitor (obscured mostly by a black wire), but near where it connects there's something brown.

Despite its quirks, this is really a good sounding receiver and I'm growing attached.
 

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Well.. pictures are waaay too small, but it looks just like one of Marantz' favourite practices: components on the solder side of the board (that's a resistor, isn't it?) with insulation and brown glue to keep them firm :yes:

Warmest regards,
Carlo
 
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