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2385 reconnect PS00 to P400 pin question

Im meeting with a friend of mine that is an electrical engineer this Monday. He will look at the RE42 and connections to hopefully find what the issue is. Hes a little worried its the volume pot.
 
Sadly my issue is with the volume pot, never was the board or connections. Testing as per photo... I may need to open it
 

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Hi Dan, where the volume stem meets the first pot there is a thin copper or brass ring, do you know how its removed to get the cover off of the first pot? ( I got the clip out but something is still holding the first cover from coming off, i have all four tabs bent back, Just dont want to pull hard unless there is something else that needs to be removed. )
 

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From looking on the internet, it looks like you might be able to slide the front metal plate with the threads off (green arrow), then remove the wafer (orange arrow).
The shaft looks to be attached to the rotating board with the brass spring contacts that slide on the carbon traces on the other layer.

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dankik said:
From looking on the internet, it looks like you might be able to slide the front metal plate with the threads off (green arrow), then remove the wafer (orange arrow).
The shaft looks to be attached to the rotating board with the brass spring contacts that slide on the carbon traces on the other layer.

View attachment 3812074
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It seems like the green piece is stuck to the wafer, i can wiggle it a bit but feel it may break the wafer if i pry any harder. Do you think it is fused due to time, if so do you believe heat will help it sperate from the wafer?
 
If your control is constructed similar to the one in this photo, my guess is that you can pull out
part 1 - bushing​
part 2 - resistor wafer​
part 3 - contact wiper and shaft​
... as one piece from part 4, the can housing. Gently see if you can pry it loose where the red arrow shows between the wafer and the metal can
Once these are removed maybe you can see what is keeping it held together.

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dankik said:
If your control is constructed similar to the one in this photo, my guess is that you can pull out
part 1 - bushing​
part 2 - resistor wafer​
part 3 - contact wiper and shaft​
... as one piece from part 4, the can housing. Gently see if you can pry it loose where the red arrow shows between the wafer and the metal can
Once these are removed maybe you can see what is keeping it held together.

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Hi again, ive tried with a bit of force but nothing is moving, . As you can see in my photo there is a slot at the end of the stem, it is not needed for the knob, The knob slides on and fastens with a set screw. Is it possible the stem is screwed on? .
 

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Whatever you do, be careful not to damage that volume pot. The 2385 volume control is apparently extremely hard to find.
sendust said:
where the volume stem meets the first pot there is a thin copper or brass ring, do you know how its removed to get the cover off of the first pot?
Click to expand...
Watch this video on how to take apart a volume control that looks almost identical in construction as yours.
He removes a ring (maybe like yours described in your post) around the shaft and is then able to slide off the threaded parrt of the control, and carbon ring to clean and lube it.
How to rebuild a volume control (Potentiometer)

The slot on the end of the volume shaft is NOT to unscrew it. Typically, it is used for providing friction tension to hold the knob onto the shaft. The metal is fragile and if you put a screwdriver into the slot to pry it you will snap off one of the sides and will need a replacement.
 
Maybe start by taking the back section off first?
Reverse of the way they assembled it.
Also check that the rivets on the defective one make proper contact with the carbon traces.
 
I watched that and 4 others before i started, in all videos after bending the first 4 tabs the threaded plate came off easy. mine doesnt move out at all, do you think penetrating oil at the shaft will help, heating the threaded part or sanding shaft to decrease diameter
 
rcs16 said:
Maybe start by taking the back section off first?
Reverse of the way they assembled it.
Also check that the rivets on the defective one make proper contact with the carbon traces.
Click to expand...
I can see the tabs that touch the wiper in the bad pot, seems like great contact. when moving volume up all is good untill half way, then it goes OL and then numbers are crazy, down after half way almost perfect.
 
Hi Rick and Dan, it does come apart only from the back, as you can see in the photo the first pot the plastic piece does not slide on like the rest, it has two tabs holding it. Im not sure i should try and release tabs, i may just clean as well as i can with what i have.. Any thought on that.
 

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Are you sure that you can't remove that retaining ring on the shaft, then slide the front metal piece and wafer off of the shaft from the front?
 
dankik said:
Are you sure that you can't remove that retaining ring on the shaft, then slide the front metal piece and wafer off of the shaft from the front?
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I removed the retaining ring before i started to disassemble. The front piece when pulling moves forward past where the retaining ring was but soon as it hits the shaft its a dead stop. I tried to hold both sided of the wafer and push the stem forward but it feels like it hits something, maybe i can use penetrating oil if its some kind of build up but it seems like there is something inside that is smaller than the shaft.
 

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Maybe the shaft needs to be rotated to a specific position to allow the front piece to slide off?
 
dankik said:
Maybe the shaft needs to be rotated to a specific position to allow the front piece to slide off?
Click to expand...
Under high magnification I can see a black collar or ring in the piece i am trying to remove. there is no way for me to get a tool in there to remove it. It stops it soon as it hits the wider portion of the shaft. I think the only chance is remove the clips on the other side. I also realized the clip i removed on the shaft was not to remove anything, it is spring steel to keep pressure back to the wafers.
 

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Hi Dan, as you can see i took the RE42 apart except for the piece that is connected with the two tabs, cleaned all of the wipers with 97% alcohol , let dry cleaned opposite side also with alcohol, then gently bent the tabs that touch the wipers out a bit to assure good contact. I then used Deoxit D100 and applied to the wipers . The three sections of the RE42 that worked before now are much more sensitive and work perfectly. The section i cleaned without taking apart, i used a flattened Qtip, it fit in nicely, also applied Deoxit 100 works perfectly at volume off but so far on full volume it starts out 50 ohms then if you wait goes down to about 3 ohms, Not sure if completely disassembling that section will make it better, i cleaned it well with alcohol and after it was perfectly dry used the d100. Thoughts on this?
 

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Hi Pete,
Good that you figured out to dis-assemble the pot starting from the back section to take apart.
lets figure out this quad pot
On p48 in the SM, RE42 is documented as two 20K-ohm(B) and two 200K-ohm(V) sections. (B) & (V), I believe define the tapers or configuration.
In a lot of pots "B" refers to a log taper, "V" I am not sure what it refers to, so you can verify. It could refer to it having the loudness tap, which have the blue wires
You can verify the taps for the loudness by measuring from each outside terminal to the taps, they should add up to the total
To determine tapers, Measuring from one of the end terminals to the middle term (wiper) as you rotate the pot(wiper) in degrees.
Usually a pot is something like 270 degrees of rotation.
When you measure from each of the outside terminals, do your measurements and confirm these value totals of ~20K and ~200K for each section?
In your post #742 you show
1) front section (1st) being 77K, but that is measuring from the right outside to the wiper, where you are having an issue
2) 2nd section 16.3K which seems right, within tolerances, for a 20K spec
3) 3rd section 255K, which seems correct for a spec of 200K. This has the loudness tap
4) 4th section 233K, which seems right for a spec of 200K. Also has the loudness tap
Are sections #3 and #4 the reverse of each other? I mean do the values from each end terminal to wiper, set in the middle, match?
Rick
 
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