Fender 15R Problem. Only 1/2 Audio Works

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UncleS

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Joined 2014
#1
Hey there.... UncleS here.

I recently acquired three small Fender amps and I am trying to get them all going. Two of them are 15R's and one 15G. The 15G needed an input plug which I have installed and it now works great.

One of the 15R's only worked when audio was put into the aux plugs. I figured the input jack might be bad. So I took the amp apart and found that the input jack was working. I then looked around the internet and found one site that suggested that two of the pc board traces from the input jack can sometime break on this model.

After close examination I found that the two traces from the input jack were broken where the corner of the PC board felxed at the input jack. (somewhere along the way the nut holding the jack to the face of the cabanite got lost and the input jack flexed causing the traces to break.)

So, I jumpered the traces with hookup wire and the amp started working again but only when I press the Drive Select button in. When the Drive Select button is out the amp does not produce sound via the input jack.

Does any body know why this is happening and how to fix this?

Thanks!
 
#3
JonSnell Electronic said:
The 15R is the same as the 15G. I take it you have a service manual.
Check pins 1 and 7 of the 8 pin op amps, they should all be at 0v with varying amounts of audio on them, signal applied. If not, check the input pins and especially the selector switch.
Click to expand...

Thanks for the reply. No, no service manual. The 15R's were purchased used for cheap and the 15G was free as it was going to be discarded. Not a manual amongst them.

I will test the op amp pins and the switches in the morning.

🙂
 
#8
JonSnell Electronic said:
The 15R is the same as the 15G. I take it you have a service manual.
Check pins 1 and 7 of the 8 pin op amps, they should all be at 0v with varying amounts of audio on them, signal applied. If not, check the input pins and especially the selector switch.
Click to expand...

Drive selector switch seems to work fine when metered on the pcb. Seems to switch properly.

Volume potentiometer seems to be working properly.

Op Amp U1 (BA4560)
With drive button out...(no guitar audio present)
Red Prob to pin - black prob to chassis with guitar as input voltage. (guitar strummed)

Pin - 8 = 15vdc
Pin 1 = .0322vdc
Pin 7 = .0433vdc

Adjusting the volume pot makes no apriciable difference in voltages.
 
#10
UncleS said:
The 15R's were purchased used for cheap and the 15G was free as it was going to be discarded.
Click to expand...

Pretty well says it all 🙂
IMO those barely work when Brand New. Resale is non existent, for Reason.
Ole Leo would have a Fit if he heard one.
Sure... you wanna bother to patch it??
Those are really poor Guitar amps Suitable/intended for 12 year old's Guitar /amp "kits", bought as unsolicited gifts. No more no less.
 
#12
Ok, so the final rap up on this one.

As suggested I pulled the U1 op amp (BA4560) and replaced it. I replace it with a Bur Brown OPA2134PA because they had them at my local electronics surplus store. But the amp still didn't work from the normal input side. 😡

So I opened it again and this time got my best magnifying glass out and took a good look at the pc board again to see if I missed something. Sure-enough, two traces were cracked also. I had missed them the first time.

So I jumpered them and the amp came to life and works great now!!! LOUD...no buzzing, very crisp and clear sounds. I love it!

Any way, thanks for the help all-ya'all!

🙂
 
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