Guitar Amp repair... desperate

[skamanic]

Hey everyone, I'm new here... reaching out for some quality instruction hopefully.

I have a Kustom Quad 100DFX, 2 channel, solid state, combo amp...
When I play on my rhythm channel is sounds... distorted... heavily and not because of my settings. It crackled an.d will occasionally pop.
I don't think a speaker is blown. But it almost has that sound.
What do I do in means of finding out the problem? Tools i'll need?
I can't find diagrams either... this has been a problem for almost 5 years now and I'm starting to get pretty bummed hahaha
Thanks for your help. I'll take instruction via email if you are altruistic and willing to walk me through this

 

[Nigel Goodwin]

You don't really give much information? - does the other 'channel' work OK.

If so, as they are only different 'inputs', then the fault can only lie in the preamp section.

But you need a circuit diagram.

 

[skamanic]

thanx

Yes the other channel works fine
So I will look for a circuit diagram
I haven't played much with electronics but I'm fairly intuitive
What tools would I need?
And what would you suggest for an itinerary?
Thank you very much for your reply

 

[Nigel Goodwin]

As the other channel is fine, there can't be much wrong really - but without a circuit I can't really other suggestions.

 

[skamanic]

So I have searched the interwebs to no avail.
Called customer service and a service dealer. They won't allow disclosure of such information.
Sorry that I can't help you help me.
Would a picture be useful? or if I sketched a diagram myself?
I've disected the amp before and I think I could do alright.

 

[ljcox]

The first step would be to swap the speakers so you eliminate the possibility of a faulty speaker.

Then do a visual inspection of the PCB looking for any obvious damage, eg. burnt components, cracks in the PCB tracks, dry joints, etc.

A good magnifying glass is essential as some problems are hard to see. For example, my TV had a dry joint that was only visible with a Mag Glass. There was fine crack in the solder around a wire.

If that fails to show anything - do you have a multimeter?

If not, there are cheap ones available.

Since you have one channel working, you could measure the voltages on the Collector, Base & Emitter of each transistor, and compare then with the voltages on the same transistors on the other channel.

 

[33by47]

can you try

https://www.electro-tech-online.com/custompdfs/2011/02/Quad100_DFX_Owners_Manual_11NOV02-2.pdf

try a the line out and cd input?

1.) Line Output - this is a 3 cond. XLR output jack for plugging into Lo-Z microphone inputs as found on PA or
recording mixers.

2.) CD/Tape Input - this 1/4" 3 conductor jack will allow you to plug in a CD player, tape or any other source to practice
along with. It sums the left and right signals into a mono signal. To control the volume of the source, adjust the output
volume of the device.

 

[skamanic]

Thanks Len and 33

Everything sounds fine through the cd input.

I don't have a 3 conductor cord for the line out jack, but on the back of the amp there is a 1/4" line out jack that didn't produce a sound through the jack and headphones; however I plugged into the "external speakers" jack in back and the problem persists on the rhythm channel, but still sounds fine on my lead channel

Len since I bypassed the speakers that should rule them out, right? I'm starting mu Inspection of the PCB now

 

[skamanic]

In addition, there are LED lights that illuminate depending on which channel is selected... the lead channel LED, which is the far left and away from the DC in and separated by the channel select switch, doesn't light up. Is that a hint? I don't know, this is the first time I've really made an attempt to understand electronics but I'm in it to win It

 

[ljcox]

Thanks Len and 33
You're welcome, it's nice to have some appreciation shown.

Everything sounds fine through the cd input.

I don't have a 3 conductor cord for the line out jack, but on the back of the amp there is a 1/4" line out jack that didn't produce a sound through the jack and headphones; however I plugged into the "external speakers" jack in back and the problem persists on the rhythm channel, but still sounds fine on my lead channel

Len since I bypassed the speakers that should rule them out, right?
Probably, but I can't be sure as I don't have a circuit diagram to look at.

I'm starting mu Inspection of the PCB now

Can you connect the headphones across the speaker that is on the faulty channel and hear what it sounds like in the headphones? Be careful not to damage your ears.

 

[ljcox]

In addition, there are LED lights that illuminate depending on which channel is selected... the lead channel LED, which is the far left and away from the DC in and separated by the channel select switch, doesn't light up. Is that a hint? I don't know, this is the first time I've really made an attempt to understand electronics but I'm in it to win It

I think that would be a separate fault. I asume the rythm channel LED does light. Is that correct?

 

[skamanic]

additonally

Yes, I have ruled out the speakers, I am going to start sketching a circuit diagram soon, Kustom won't give them out...

EDIT: I'm sure I'm more appreciative of your input haha
I've had this problem for years and am just now starting to take it seriously. Furthermore,do you have any resource suggestion you could refer me to to aid my learning process?

Yes that is correct and I figured they were separate

 

[ljcox]

You could start with the Theory section of this forum.

There are also tutorials on other electronics forums.

 

[ljcox]

See this thread.

Service manual or circuit duagram for Guitar Amp Kustom Quad 100DFX

 

[clel miller]

Is the amp single or dual input, one or two input jacks.?

 

[ljcox]

It has a single input jack, but also has an input for a CD ot Tape recorder.

 

[clel miller]

As others have said, you are going to have to pull the chassis if you want to go any further. First thing I would check when I got in there is the TRS input jack. It is possible you have lost continuity to the rhythm channel, especially if it is a crappy jack that is soldered directly to the crappy PCB. If there is nothing wrong visually, I would just re-flow the solder on that jack and see what happens. If it is still bad, start chop-sticking with a guitar running through the amp and see if you can find a bad part. If that does not fix it, I would follow the advice some of these other guys have given you.
Good Luck

 

[skamanic]

Haha thank you and its already pulled I'm slowly trying everything thats been referred to me.

And thanks for answering that input question Len