Trimmer pot replacements? (Bourns, etc.)

ssouci

Well-Known Member
hi, I'm looking for some trimmer pot replacements for my Marantz 2275 and 2230... (eg. 10-turn, 25-turn, etc. like those made by Bourns, etc.)

the originals drive me crazy, because the adjustment is so very touchy and very difficult to get dead on... the slightest bump, and the reading moves! (DC offset adjustment, etc.)

hoping for something that will drop right in and that I can still access for easy adjustments... also, looking for a good big supplier of these (hopefully in Canada)

I looked in my units and they are labelled:

2275
-------------------
R742: "202f6"
R7??: "202f6"

2230
-------------------
R760: "472-100K(ohm symbol)B"
R765: "472-470(ohm symbol)B"

thanks for any suggestions for the "best ones" to use!

the PHOTOS shows the backside of the 2 pots on the 2275, the white plastic parts (in the top-left corner), and also the 2 pots on the 2230 with adjustment screw (at top of amp module):
 

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The reason they are so touchy is because it is an open trimmer and after sitting at it's setting for 40 years it can get pretty crappy and touchy.

IMO there is no need for anything but a single turn. A good single turn when put in is not touchy but precise and they are sealed units. I favor the Bournes 3329 series they cost a bit more but track excellent fit well and are easily adjustable.

This would be what you may use on the 2275, the SM says a 1K and a 2K, but like the 2245/2270 I think they are both actually 2.2K as per what you say they are labled.

I can not see if the wiper is top or bottom in your pic: so below is an example:

http://www.digikey.com/product-detail/en/3329X-1-202LF/3329X-202LF-ND/1088273
 
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single turn sounds fine, because I think the originals are like that

do you know if a single part # can be used in the 2 amplifier trimmer positions on BOTH the 2230 and 2275?

thanks
 
no because the values are different on the 2275 and 2230.

Question are you able to adjust your 2230 or is it jumpy?
 
no because the values are different on the 2275 and 2230.

Question are you able to adjust your 2230 or is it jumpy?

2230:
making one setting is "OK", the other very jumpy... the value will change even if there is no rotation, rather just the slightest "bump" in my twisting motion... I have to go back/forth 20 times until I get it to settle in the right spot by chance

2275:
I think it was very similar to above (but haven't done it for awhile)

on the other hand, I've always wondered how accurate these settings need to be?... for eg, is 11.0V necessary or would 10.2V still be OK? (fake numbers)
 
2230:
making one setting is "OK", the other very jumpy... the value will change even if there is no rotation, rather just the slightest "bump" in my twisting motion... I have to go back/forth 20 times until I get it to settle in the right spot by chance

2275:
I think it was very similar to above (but haven't done it for awhile)

on the other hand, I've always wondered how accurate these settings need to be?... for eg, is 11.0V necessary or would 10.2V still be OK? (fake numbers)

Yes close enough.

Make sure you think it through you have 2 functioning units and if you are replacing the trimmers as a first time you need to be very careful as to rotation when installed because each channel may go in opposite directions. You can measure the old ones when removed and preset the new ones. The bias circuit will dictate the direction.
 
what about CLEANING these things?... I have used Dexoit D5 5% spray before, plus lots of turning back & forth, but I don't think it made much difference

what about using 100% strength red liquid Dexoit... might that help?... or another method or chemical?...

it would be much easier & safer to keep the exiting trimmers, and I'd be happy if they were just a bit more adjustment-friendly
 
IMHO you will be much better off going with new Bourns trimmers. The old ones may not be reliable even if you Deoxit them.

There is a small learning curve, and I have only been through the process a few times myself. But once they are in it is well worth the time.

Like Pat says, measure the resistance settings from the old trimmers AFTER the bias (or DC offset) is adjusted correctly. Remove the old trimmer and measure pin 1-2, 2-3, and just to be sure you are installing the right value measure pin 1-3 too. Write those settings down somewhere being certain to keep L channel separate from R. First time maybe do just one trimmer at a time so that any errors can be caught quickly. Adjust the new trimmer as closely as possible before installing. Then after it is in place check bias (or DC offset) as soon as the unit is turned on then watch it while the unit warms up.

There are 3 pins on a trimmer. Pins 1 and 3 are the nominal value of the trimmer. Pin 2 is the wiper. The datasheet is very helpful. Play around reading values between pins then turning the adjustment.
 
thanks so far everyone...

I'm wondering if I might be able to order *just one* Bourns part # to use in all 4 locations?

seems like those for the 2230 and 2275 are quite different... here's all the info including what the service manual lists

2275
-------------------
R741: "202f6" (SM = trimming 2Kohm (B))
R742: "202f6" (SM = trimming 1Kohm (B))

2230
-------------------
R760: "472-100K(ohm symbol)B" (SM = trimmer 100Kohm+/-25% B)
R765: "472-470(ohm symbol)B" (SM = trimmer 470Kohm+/-25% B)

what do you think?
 
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As mentioned before each trimmer has a different value, so you will need to match each position. The 2275 seems like it is like the 2270 which actually uses Qty 2 of 2.2K for each amp module. So yes for the 2275 you can order 4 of the same bournes trimmer.

For the 2230 you will need 2 @100K and 2 @ 470 Ohms not "K"

I have the ones for the 2275 here if you need the Mouser part# let me know.

I can also provide part numbers for 2230.





thanks so far everyone...

I'm wondering if I might be able to order *just one* Bourns part # to use in all 4 locations?

seems like those for the 2230 and 2275 are quite different... here's all the info including what the service manual lists

2275
-------------------
R741: "202f6" (SM = trimming 2Kohm (B))
R742: "202f6" (SM = trimming 1Kohm (B))

2230
-------------------
R760: "472-100K(ohm symbol)B" (SM = trimmer 100Kohm+/-25% B)
R765: "472-470K(ohm symbol)B" (SM = trimmer 470Kohm+/-25% B)

what do you think?
 
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As mentioned before each trimmer has a different value, so you will need to match each position. The 2275 seems like it is like the 2270 which actually uses Qty 2 of 2.2K for each amp module. So yes for the 2275 you can order 4 of the same bournes trimmer.

For the 2230 you will need 2 @100K and 2 @ 470 Ohms not "K"

I have the ones for the 2275 here if you need the Mouser part# let me know.

I can also provide part numbers for 2230.

Patfont:

sure, I would love the part #s if possible!

(there are so many of these darned trimmers available...)
 
I will def say the trimmers in the 2245/2270 and 2275 are turds, but I have not had a problem with the ones in the 2230, you may have other problems.:scratch2:

Proceed with caution and at your own risk, you have 2 working receivers.


http://www.digikey.com/product-detail/en/3329P-1-501LF/3329P-501LF-ND/1088250


http://www.digikey.com/product-detail/en/3329P-1-104LF/3329P-104LF-ND/1088243


http://www.digikey.com/product-detail/en/3386H-1-202LF/3386H-202LF-ND/1088512



Patfont:

sure, I would love the part #s if possible!

(there are so many of these darned trimmers available...)
 
I will def say the trimmers in the 2245/2270 and 2275 are turds, but I have not had a problem with the ones in the 2230, you may have other problems.:scratch2:

Proceed with caution and at your own risk, you have 2 working receivers.


http://www.digikey.com/product-detail/en/3329P-1-501LF/3329P-501LF-ND/1088250


http://www.digikey.com/product-detail/en/3329P-1-104LF/3329P-104LF-ND/1088243


http://www.digikey.com/product-detail/en/3386H-1-202LF/3386H-202LF-ND/1088512


Patfont:

fantastic and thanks so much for hunting down those part #s --- hugely appreciated, because there seem to be so many variations of these things

great to see from Digikey as well, since that's where I plan to order all my parts from today (finally...) for my RE-recap of my 2230 and 2275

gotta love AK
 
I hope all goes well on your work.

Just know that replacing a trimmer in not like replacing a cap. They are sensitive circuits and on some the adjustments have to be correct. I forget, but have you built a dim bulb tester?
 
no dim bulb tester...

however, I'm thinking I will use my basic multimeter to measure resistances across the 3 pins to get things in the ballpark before installing & powering up (ie., try to match the old part I removed).... that should be OK ????
 
This is only me, but someone else is welcome to jump in. You have not done this before I will say a dim bulb tester is mandatory, $20.00 from Lowes and 15min. to assemble. (It just makes good sense for insurance)

It is easy to get confused quick measuring the old trimmers, as in the 2275 one set has to be removed to even measure, you can not measure in circuit. The other set you can.

Bias circuits can be of the same- as in you turn to the right for both and they do the same thing.

Mirror imaged-as in you would turn away from each other to arrive at your setting.

or turn inwards to each other to arrive at the same setting. You need to look at the board to see which leg is on the same trace as the wiper in the circuit.

Your idea- measure and get close can work, but I would not do it without the DBT.:D







no dim bulb tester...

however, I'm thinking I will use my basic multimeter to measure resistances across the 3 pins to get things in the ballpark before installing & powering up (ie., try to match the old part I removed).... that should be OK ????
 
I think Pat makes a lot of good points. This would need to be done right.
ssouci, I have not followed your threads so I am not able to assess your skill level.

But if you are confident in your soldering and organizational abilities then, IMHO, this can be done without a DBT. I have changed trimmers in 4 amps now with no issues.

My previous post was not as clear as it could have been, hopefully this is an improvement:

(assuming that you have the correct new trimmer and the pins will match up to your PCB)

1) set bias and/or DC offset with old trimmers in place
2) remove one trimmer and identify Pin 2, it should have some type of marking to differentiate it from the other pins
3) measure and write down resistance readings pins 1-2 and 2-3. I draw myself a picture when doing this.
4) measure and write down resistance reading pins 1-3. This is the nominal value of the trimmer but it may not match precisely either the value in the parts list or the value of the new trimmer.
5) on the new trimmer measure the resistance between pins 1-3. this is simply to verify that you are using the correct trimmer (or as close as you can get from the parts supplier)
6) on the new trimmer, approximate as closely as possible the values between pins 1-2 and 2-3 (from step 3) In my brief experience it has not been possible to get these exact.
7) install new trimmer making sure to get Pin 2 in the right hole. Fire up the amp with DMM leads attached to appropriate test points so that you can immediately spot any potential issues. Be aware that when the amp is cold you will probably not be seeing the correct readings. Just don't let bias or offset go way high. Once the amp is warmed up set to correct value.
8) repeat steps 2-8 for remaining trimmers

good luck

OTOH, it is good to have a DBT around too....
 
I think Pat makes a lot of good points. This would need to be done right.
ssouci, I have not followed your threads so I am not able to assess your skill level.

But if you are confident in your soldering and organizational abilities then, IMHO, this can be done without a DBT. I have changed trimmers in 4 amps now with no issues.

My previous post was not as clear as it could have been, hopefully this is an improvement:

(assuming that you have the correct new trimmer and the pins will match up to your PCB)

1) set bias and/or DC offset with old trimmers in place
2) remove one trimmer and identify Pin 2, it should have some type of marking to differentiate it from the other pins
3) measure and write down resistance readings pins 1-2 and 2-3. I draw myself a picture when doing this.
4) measure and write down resistance reading pins 1-3. This is the nominal value of the trimmer but it may not match precisely either the value in the parts list or the value of the new trimmer.
5) on the new trimmer measure the resistance between pins 1-3. this is simply to verify that you are using the correct trimmer (or as close as you can get from the parts supplier)
6) on the new trimmer, approximate as closely as possible the values between pins 1-2 and 2-3 (from step 3) In my brief experience it has not been possible to get these exact.
7) install new trimmer making sure to get Pin 2 in the right hole. Fire up the amp with DMM leads attached to appropriate test points so that you can immediately spot any potential issues. Be aware that when the amp is cold you will probably not be seeing the correct readings. Just don't let bias or offset go way high. Once the amp is warmed up set to correct value.
8) repeat steps 2-8 for remaining trimmers

good luck

OTOH, it is good to have a DBT around too....

Roger2:

thanks for the detailed info!... I think I will try doing this, because in my experience, trying to get the adjustments set with the useless old pots takes a lot of time and is frustrating... plus, you have to wonder how well those pots can *hold* the settings over time?... will even the slightest bump on the receiver screw up the settings?

can you (or Patfont) confirm that the pin layout (a "tripod" formation) from old part to the suggested new Bourns parts will be a direct match, or has anyone ever had to bend pins, install upside down, or ???

thx
 
well said roger2 but............

So is he really going to install one trimmer on the 2275 and then reassemble set trimmer etc and then do it again. That is like 4 RandR's to do both amp modules granted the 2275 is an amp module but it still has to be opened up to solder and have to take care of that bias diode.

Some do this although I do not

offset trimmers=adjust to center
bias=set for min. bias current







I think Pat makes a lot of good points. This would need to be done right.
ssouci, I have not followed your threads so I am not able to assess your skill level.

But if you are confident in your soldering and organizational abilities then, IMHO, this can be done without a DBT. I have changed trimmers in 4 amps now with no issues.

My previous post was not as clear as it could have been, hopefully this is an improvement:

(assuming that you have the correct new trimmer and the pins will match up to your PCB)

1) set bias and/or DC offset with old trimmers in place
2) remove one trimmer and identify Pin 2, it should have some type of marking to differentiate it from the other pins
3) measure and write down resistance readings pins 1-2 and 2-3. I draw myself a picture when doing this.
4) measure and write down resistance reading pins 1-3. This is the nominal value of the trimmer but it may not match precisely either the value in the parts list or the value of the new trimmer.
5) on the new trimmer measure the resistance between pins 1-3. this is simply to verify that you are using the correct trimmer (or as close as you can get from the parts supplier)
6) on the new trimmer, approximate as closely as possible the values between pins 1-2 and 2-3 (from step 3) In my brief experience it has not been possible to get these exact.
7) install new trimmer making sure to get Pin 2 in the right hole. Fire up the amp with DMM leads attached to appropriate test points so that you can immediately spot any potential issues. Be aware that when the amp is cold you will probably not be seeing the correct readings. Just don't let bias or offset go way high. Once the amp is warmed up set to correct value.
8) repeat steps 2-8 for remaining trimmers

good luck

OTOH, it is good to have a DBT around too....
 
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