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VR resistor question

R

Rymdis

Member
Hi there!

I have a burned one 100 ohm VR resistor and was wondering it that could be replace with a 1k ohm resistor? I have marked the VR with a red circle on the pictures. This VR adjust the idle current. I have no idea what will happen if i use a bigger one :) Mybe some wiz can help me out looking at the schematics. Its in an Pioneer SX550. It will be harder to pinpoint the exact current but i just wondering if its safe to use a 1k VR?


Many thanks
 

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A designer will target a pot to have a useful range on it's adjustment. If it was mid scale, then it was using about 50 ohms.

Ideally, you'd check an identical one in another part of the circuit and see if that's about right. Then take your 1K pot (you are referring to using a pot, right?) and see if with an ohm meter you can comfortably adjust it in the 50 ohm (or whatever value is really in use) range. Chances are, that'd be difficult and it'd be tough to get a reliable value and be risking the output transistors.

So while you can possible achieve the running value, adjustment would be very touchy and tough to have be very stable. Not really such a good idea when you can wait a few days and get a correct value and not risk further problems!

Good luck and hope that's all the issues you've got in there!

Mark
 
Thanks for the answers!

Yeah, this amp is a mess, thats for sure :) But using a 1k Pot wont destroy anything, right? And i could see if adjusting it to 50ohm and around is very tricky.
ill see if 0-100ohm is out of range when turnings it. But if i manage to get it right, will it not be stable then?


/R
 
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The slightest twitch will overbias the output stage, and you'll have a rather dead amplifier. Not recommended. Get the proper part.
 
But if i turn it to 50ohm just for testing pruposes, then that would be ok, or? I wouldnt touch it when its on as i saw it was VERY sensitive :)

/R
 
EchoWars said:
Put a 4.7~10 ohm resistor in there if you just want to test for functionality.
Click to expand...

cool! As im no electrician i have to ask how to put this resistor. The Pot has three legs. In which two holes should i solder it? When i check the Pot there are two legs that gives the maximum resistance of that pot. is it in these two holes i should put the resistor?

thanks
 
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Can't tell from here, but two of the holes where the original trimpot was mounted are likely on the same foil trace. One side of the resistor would go here (either hole, since they are at the same electrical potential), and the other side to the third hole.

If you get this wrong, Bad Things™ will happen.
 
EchoWars said:
Can't tell from here, but two of the holes where the original trimpot was mounted are likely on the same foil trace. One side of the resistor would go here (either hole, since they are at the same electrical potential), and the other side to the third hole.
Click to expand...

I dont know the term "foil trace" :(

but ive made a pic of a pot that ive numbered the legs. from what i understand the resistor should be either in hole 1 or 2 and in 3? I took a 100 ohm pot as example.

and why use such low as 4.7~10 ohm resistor ?


thanks for the help. really appreciate it!!!
 

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Look at the back (solder-side) of the board. Two of the traces should be on the same foil.
 
ah, you mean the copper-foil? From Sweden so i have some problems with these terms :(

Yes, there are two pins on the same copper-segment and one pin on another. Should one leg of the resistor be in one of the two holeson the same copper-sgement amd the other leg in the other hole then?

ive attached a pic where the pot used to be. Sorry for nagging but i just want to be sure here :)

the two left are on the same foil and the right one is on another.

and is there a reason to use such a low resistor?


thanks
R
 

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The single resistor needs to be mounted in the position of the "red" line. The white line is pointing to a torn foil trace.You will need to do a little repair work there when the time comes...
 

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avionic said:
The single resistor needs to be mounted in the position of the "red" line. The white line is pointing to a torn foil trace.You will need to do a little repair work there when the time comes...
Click to expand...

ok, thanks. But i dont understand why to use a low 4-10 ohm resistance here? What is the benefit?

yeah, some repair is on the way :)
 
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