Fender Sidekick 25

[GuitarGuru]

I have a Fender Sidekick 25 Reverb. The output was low with a ground noise. I checked all the connections on the board. It's very clean. I replaced the IC's and the 3 Transistors on the Heat Sink Plate. Not any better. The headphone out and preamp out to another amp do the same thing. I do have the schematic. Any help would be great.

[DrGonz78]

List all the troubleshooting you have done on the amp with more details. Right now it appears that you checked all the connections on the board. Explain more here by exactly what you did? For example, did you do any troubleshooting on the speaker or anything else. Faulty IC chips passing signal will have a 120hz signal hum as they are located in the preamp side of things. Did you test any voltages before pulling out the IC chips? And what are those 3 transistors you replaced on the heat sink? Was wondering if you tested those before pulling them to replace? Just need some more info to get the ball rolling.

Edit: Good luck Also, I get that you tested the amp through the preamp out/headphone jack, so it is probably not the speaker. But is there any DC voltage on the speaker leads or anything like that?

There is also the right schematic here from Jazz P Bass for anyone's reference...

http://music-electronics-forum.com/t17821/

[GuitarGuru]

Yes the speaker works. I guess I should plug it in and check the voltages?

[Jazz P Bass]

Check the power supply voltages.
Specifically the preamp ic power pins. (pin 4 & pin 8)
Did we try plugging into the power amp in jack?

[GuitarGuru]

The amp is making a loud noise and none of the front panel controls change anything. I don't think the Power Amp Input on the back will work either. I'll check the power supply voltages. Can I just go right to the speaker leads?

[Jazz P Bass]

Yeah you can 'check' the speaker leads.
If there is any voltage there (Vdc) you have a power amp problem.
I still recommend checking the actual power supply.
The voltages are not marked on the schematic.
But working from it we can pretty well guess Point A & B will be about +30 Vdc & - 30Vdc.
C & D will be about + - 22 Vdc.
And E & F will be + - 16 Vdc.

[GuitarGuru]

No Voltage to the Speaker Leads. Opened it up, plugged it in, with the speaker attached because that could put a load on it.
I guess I'll have to pull the board out to get to those points. Here's a picture of the inside.

[Enzo]

It is a solid state amp, it does not require a load. It is only the tube amps that MUST have a load.

NO DC on the speaker but lots of hum? My first suspects are the main filter caps, did you resolder them? You should, even if they "look OK".

[GuitarGuru]

I checked the 2 connections with power on. I get -50mV. I'm going to pull the board and try the contact points under it.

[DrGonz78]

That seems like no voltage at all coming off the PT and makes me wonder how you measured this first voltage test just to makes sure... Either that or it's just bad.

[GuitarGuru]

Auto Multimeter set to 10 Megohm Input DCV, Red on bottom red wire in picture, black on top black wire.

[Jazz P Bass]

Uhm...
See that little rectangular box around the red & black wires.
The one that says 'ac'?
That is the power transfomer secondary.
The middle pad is the grounded center tap.
Vac.
The small square thingy on 4 legs is the bridge rectifier.
D15.
The one corner is marked '+'.
That is your B+ voltage. (TP A)
Vdc.
The rectifier legs are set up as: +, AC, -, AC.
So the B- (TP B) would be directly across from the B+ leg.
Measure those two points.
Vdc.

[GuitarGuru]

Measured with the power on 33mV. The corners were 19mV. Added a picture. Thanks.

[Jazz P Bass]

That is one way to measure.
Personally, I would have put the black lead on chassis ground.
Red lead stays where it is. On the + of the BR.
That would measure the B+.
The black lead where it is & the red lead to ground would have you measuring the B-.
And your meter is set to read volts dc?

[GuitarGuru]

OK, so the Power Supply is good? What now?