Severe humm in Squier Champ 15G guitar amp by Fender - diyAudio
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Old 9th September 2005, 04:11 PM   #1
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Default Severe humm in Squier Champ 15G guitar amp by Fender

Squier Champ 15G guitar amp by Fender
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Ok , I'm trying to find some information on the above amp , the one I have has developed a severe humm / static coming through the speaker when turned on with or without guitar pluged in . I'm assuming it is the transformer .The transformer is showing 16.4 volt ac on both + leads . question is what should the output be for this transformer of does anyone have a service manual / wiring schematics diagram for this amp . I contacted fender company and was told they had no longer had information on this amp and could not offer any suggestions . Any help would be appreciated.Also if I appear to be lookingin the wrong direction with the transformer being the problem I'd appreciate any suggetions on other possible causes .
Thanks
Fort
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Old 9th September 2005, 05:22 PM   #2
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I think the voltage U are reading (16.4VAC) on the seconday of the power transformer is probably correct. The hum you are hearing is probably caused by a bad filter capacitor in the power supply. These are big electrolytic capacitors and they can go bad and cause the problem U described. Lemme know if U need further assistance. I work on amps all the time.

Bob

bob4analog@yahoo.com
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Old 10th September 2005, 03:20 AM   #3
Enzo is offline Enzo  United States
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The transformer is just about the last thing likely to be bad. It would not cause hum in any case.

There are two kinds of loud hum in little amps like this. Either the amp makes hum and nothing else, or the amp basically functions but loud hum is added to the music.

If the music comes through with the loud hum on top, then the filter cap is probably cracked free of its solder, or the input jack is broken free of its solder. If the hum is present even with ALL the controls set to zero, then the filter cap is suspect. The cap itself could be bad, but it is far more common for the solder to be bnroken.

If the hum can be turned up and down by some control, then it is coming from the preamp and the input jack is the first place to look.

But if the hum is loud and there is no music at all in there, check the output for DC voltage across the speaker. Another way is to simply look at the speaker cone. When you flip the power on, if the speaker cone moves one direction a bit and stays there, that is DC on the output. Don't leave it on any time please.

If ther is DC on the output, the output device on the board is bad. it is probably a TDA2030 or TDA2040. Those are five leg things that look like a TO220 tab top transistor. It will be on a heat sink.

I don't recall any Squire amps using anything more sophisticated than that.
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Old 10th September 2005, 03:41 PM   #4
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The music comes through with the loud hum on top , you can turn the gain and vol down to half or less and the humm is annoying but useable , even with both gain controls and the vol set to 0 there is still humm from the speaker . There is no DC voltage across the speaker ,so will check solder joints first and post results.
Thanks
Fort
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Old 12th September 2005, 08:59 PM   #5
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Ok , pulled the electronics from the amp , visual inspection showed no bad solder joints under 10x mag so pretty sure thats not the problem .There are 2 caps rated 2200uf 35V , checked each one while in circuit , *unpluged and discharged* with a DVOM , set meter at 200k ohm and checked first cap , runs up to 200k and stops and charge holds , checked second one and it goes to 10.5k and stops , discharges instantly after removing meter and reapplying . There is also a cream colored almost like hard plastic substance that is connecting the 2 caps at the base .Thicker at the cap that reads 10.5k and tapers down to where it meets the other one .I'm guessing that is where it has leaked and is bad ? Show mercy on my apparent lack of knowledge , I lost the first 20 years of my life and memory "which included most all of my knowledge of electronics " due to a closed head injury from a motorcycle wreck and am starting over with electronics as rehab / hobby so bear with me as it'll get better .
Thanks
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Old 12th September 2005, 08:59 PM   #6
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Oh, the caps are both :

Rubycon
35v 2200uf
CE W
2M111
85 degree c
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Old 13th September 2005, 04:47 AM   #7
Enzo is offline Enzo  United States
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That cream colored stuff is just hot melt glue. They glue down larger parts so they don't break free as easily from vibration. Go ahead and chip it away with a screwdriver. I usually replace it with silicone after service.

Looks like one is bad. The one that charged up well was probably OK. Your meter sends out a volt or two on resistance scales, and the cap charges up to this. FLip the meter over top volts, and there should be that volt or two sitting there slowly discharging. if it drops instantly, the cap is bad.

It is a 2200uf electrolytic at 35VDC. You can go to 50v if you have them instead. You can also go up to 3300 uf or something if you have those. Just don't go lower. The values are not critical, but you also want to watch physical size so new ones fit.

Make sure to put them back in the right way, they do have polarity and there is one for positive and one for negative.
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Old 13th September 2005, 04:18 PM   #8
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Enzo , thanks , you also answered my next question too about going up in size , I was 99% sure I could go up but not down so thanks for the reminder Some things are still in my head but makes me wonder about the accuracy of the info sometimes. I'm assuming that with the low cost of the cap I should just go ahead and change both , 1 so they match and 2 just so the odds of the second one going bad soon and having to open it up and replace it is at its lowest.Would cost more in time to take it apart *if I was getting paid* than to just change it to begin with .
Thanks again for everyones help.
Tim
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Old 13th September 2005, 04:18 PM   #9
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Ok , replaced the cap that was bad with one I had on hand that had same specs just was about 1/8 inch taller but height not a problem .left the second one for now , connected everything back up and humm was almost all gone , then a little more then pop the cap blew after about 90 seconds .The cap I replaced it with was old , perhaps 10 year+ pulled from another piece but appeared good , tested right I thought , wanted to be sure it would take out the humm before I tried to get new ones . put it in in the same way as the old one came out but perhaps I reversed it , would that have caused it to explode or just age itself of the cap .only markings on the board is a circle around where the cap sits with a half circle around the hole for what I thought was the - neg leg of the cap . the same way the second cap is in , or are the 2 supose to be reversed ?
I hate drain bammage .
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Old 13th September 2005, 04:18 PM   #10
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Ok , drain bammage aside I went back over it and did find I reversed the cap polarity so this one was human error .
Off to change it again .
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