Help with resistor replacement


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Old 08-28-17, 12:38 AM
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Help with resistor replacement

Hi everyone, sorry to drop bomb a question on new forum. (not comfortable carry out this repair without some knowledgeable advice)

I've identified 3 resistors in my guitar amp that are faulty and need replacing, took them out and I wasn't having much luck identifying their rating, only place in town that could help me didn't have the same ones and he's given me some that are slightly different, said they should be fine...

I'm not comfortable fitting these because after trying out some online rating calculators Ive come out with the results of 22k ohms 5 colour bands being replaced with 2.2m ohms 4 colour bands (correct me if im wrong), Ill attach a picture of both old and new.

Any help would be much appreciated, and im happy to provide more info if required.
 
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Old 08-28-17, 01:02 AM
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Here's the pic. also, on the parts listing of the circuit board, the original resistors are listed as, 22k-1/4w-5*
 
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Old 08-28-17, 02:47 AM
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...or is anyone able to tell me what I should be searching for to replace them with matching new ones?..
 
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Old 08-28-17, 04:29 AM
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Hi Jackson and welcome to the forum.
You are correct, that would not be a good replacement. What you want is a Red, Red, Orange for the first three colors. The fourth color is a tolerance so gold or silver would be fine but your 5* may be signifying 5% so gold if you can find it.

Note his Red, Red, Green is 22 times 10 to the 5th power or 5 zeros, thus the 2.2 meg you stated. (that's for other readers in the future).

Bud
 
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Old 08-28-17, 04:36 AM
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Too hard to see on my phone, I can only see color 4 bands, I can't tell which ones in the pic are 4 bands and which are 5. Here's a link to an online calculator that should help you. Just click the correct button for the # of color bands:

https://www.digikey.com/en/resources...or-code-4-band

Edit: In rereading your post, I see that the old ones on the bottom have 5 bands. They are very different.
 

Last edited by JoeWilson; 08-28-17 at 05:21 AM.
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Old 08-28-17, 07:12 AM
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Short answer: You would want to find resistors with the same color band pattern.

I see the old resistors on the bottom with just 4 bands, and with a value of twenty two ohms and not 22K.

(Starting from the end with a non-metallic band, red for 2, red for 2, black for add no zeroes.)

The gold band further on stands for resistance value plus or minus 5%.

Double check the schematic or parts list or circuit board markings.

Don't forget that, when measuring resistance, turn off the power and also one of the two places you touch the meter probes to must be unhooked from where it was connected (or if it is a terminal, have all other wires unhooked from it.)
 
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Old 08-28-17, 07:23 AM
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Now confused as he posted "on the parts listing of the circuit board, the original resistors are listed as, 22k-1/4w-5*"
I agree, if those are the ones he removed they are not 22K.

Bud
 
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Old 08-28-17, 07:57 AM
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Now confused as he posted "on the parts listing of the circuit board, the original resistors are listed as, 22k-1/4w-5*"
I agree, if those are the ones he removed they are not 22K.
That's where I got confused, he also said the originals had 5 bands, so I assumed that there was a color in between the last 2 that I couldn't see on my phone. It would have to be red to be 22K, which we'd be able to see, so it's not a 22K. I assumed it was yellow making it a 2.2M.

A 4 band Red, Red, Green, Gold is also a 2.2M, so they'd be the same.

If the old ones were 5 bands (Red, Red, Black, Yellow, Gold), and the new ones have 4 bands (Red, Red, Green, Gold) they are the same.
 
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Old 08-28-17, 08:43 AM
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I never had 5 band resistors to work with so not used to the separation between bands, but I enhanced that image as best I could and a fifth band did not show up. My guess is those bottom resistors are 22 ohms and that leaves the question as to what the parts listing is vs what was on the board. Certainly wouldn't want to install 22 ohms where a much larger resistor should be.

I'll wait for Jackson to clarify.

bud
 
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Old 08-28-17, 09:50 AM
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The picture is of the ones he received as replacements.

He needs the 22k @ 5% which is the red-red-orange-gold.

Pretty rare for a 22k to go bad so be sure to check yours with one side disconnected.
 
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Old 08-29-17, 05:31 AM
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Easy to check he two resistors that are already detached from the board as shown in the picture.
 
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Old 08-29-17, 08:15 PM
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Thumbs up

Champions, thanks for the reply.

Ive just noticed the schematics are from 1999, and this is a far more recent model. (always good to check the fine print, trying to find more recent prints)

*Regardless, Im definitely taking the option of replacing them with identical resistors as the ones removed*

The lady at our local Jaycar is able to order in some, but she says she needs to know which ones they are (its at this point I got confused) I've tried the online calculators, and there doesn't seem to be and option for 5 band resistors with white as the 5th band, so I've entered in as 4 band (Red, Red, Black, Gold) and its results show..

22ohms 5%... once again, this is disregarding the white band.

So basically my final questions, Is 22ohms 5% what I request at Jaycar, or eBay as another option, Or are these resistors identified with another specific name/listing?

Thanks again guys.
 
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Old 08-29-17, 08:52 PM
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Pretty sure those are standard 4 band resistors.
A guitar amp would not usually need 5 band precision resistors.

Based on your picture..... you need 22 ohm 1/2 watt 5% resistors.
From Jaycar... jaycar/22-ohm-0-5-watt-metal-film-resistors/RR0532


Ive just noticed the schematics are from 1999, and this is a far more recent model.
It is extremely unlikely that the design changed from 22k ohms to 22 ohms. The k probably should have been ohms and the improvement would be from 1/4w to 1/2w size.
 
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Old 08-29-17, 09:38 PM
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Just curious... how did you identify those resistors as faulty? What do they read now?
 
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Old 08-30-17, 01:32 PM
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They don't look bad to me-I've seen em burnt,brown,&blistered and still ok.
 
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Old 08-30-17, 02:09 PM
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BTW you can get phone apps for resistor color codes. Mine agrees that it's a 22 ohm 5% resistor.
 
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Old 08-30-17, 06:37 PM
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As others already mentioned, it is very rare for resistor to go bad unless it is burnt, which will show visible signs.
How did you come to the conclusion your resistors are bad?
 
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Old 08-31-17, 01:37 AM
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Someone online had the same problem and he identified 3 faulty resisters (labelled r18,r107 &r108 on the circuit board). This amp belongs to my cousin, its the same model as mine, so we swapped out circuit boards to narrow down possibilities, and could confirm that it is the board that the 3 resistors are on, so in good faith we're just gonna replace them and hope for the best, and yeah.. the guy at the auto electrical place tested them with a multi-meter and 2 out of 3 are faulty. He got out the 3 with green bands and said that's the closest he had.

As soon as the replacements get in I'll post the results.
 
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Old 08-31-17, 07:49 AM
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I have years of board repair experience as do others here and yes you can have a bad resistor, but no it did not fail by itself. If a resistor is cooked something else took it out. (99% probability)
As for "the guy at the auto electrical place tested them " I would have no confidence in his advice.

Bud
 
 

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