Fixing a broken pot

[2fast4u88]

I have a older model jensen amp. A ka-3 that has been a good little amp. Till today it went into protect mode. Which I hope came from the pot breaking off the board. It doesn't have much of prongs to solder it back on as I tried.

Trying to figure out what to use to fix this thing. As the pot looks to say b30k on the side. Looks like it was stamped a few times. But it is for the bass boost on the sub side of the amp. Any help would be nice.

Hoping to maybe pick one up a radioshack or something. It doesn't have to be the same length or have the teeth on it for the knob I guess. But has to be the rectangle type pot not a circle one. Thanks for any help

 

[Perry Babin]

Mouser may have something that will work but they don't have a 30k. Click HERE.

 

[2fast4u88]

I have no idea what I am look for though Cept what I already said. If no 30k what would happen using a smaller than 30k or bigger? I would guess more range or less.

 

[Perry Babin]

You'll have to measure the pin spacing on your pot and then find one to match. I don't know the circuit so I can't say whether a 20k or a 50k would be a better substitute. They're only ~$2 each so order one of each.

Are you certain that there aren't other problems? Have you checked the output transistors?

 

[2fast4u88]

I think that is all. It will come on thump. It played once for a sec. Then goes in protect mode. Inside the amp looks brand new. Nothing burned or anything. When it did play for a sec you could tell the bass boost was loud as crap. Should I check anything else. If so what would I look at?

I can snap a picture of it if that would help.

 

[Perry Babin]

Can you post a clear, close-up photo of the top and bottom of the board where the potentiometer has broken off of the board?

 

[2fast4u88]

yea I can do that in a few. It is a 3 prong square one.

 

[2fast4u88]

First pictures is where it is broke then the last is a shot of the board. Sorry not really clear. Someone broke my hd sony cybershot. So I had to buy another cyber shot that is retarded. Have yet to figure out all the settings.

 

[Perry Babin]

It appears that there is no connection (top or bottom) to the solder pad closest to the other potentiometer? Is that true?

 

[2fast4u88]

Are you meaning the pads for the one that broke off or other pot beside it?

The one that broke off. Two prongs are hooked together on the solder pad. The two to the right in the top pic. The other is spaced a hair. As for speaking of the other pots they are spaced out. Unless you are asking where it traces to. I would have to look.

 

[Perry Babin]

If the two pads nearest the other pot are connected together by a trace, connect all 3 pads together and power up the amp to see if it goes into protect mode. You should have all semiconductors clamped tightly to the heatsink when you power up the amp. If you don't and there is a problem, significantly more damage could be done.

 

[2fast4u88]

Um in the top 2 pics if you look. They are the very top most left pads. Not including the first one. Just the 3 to the left from there. As for the next pot. It is two stips over to the right from the solder pads on the broke off one. Then is those 6 close together dots from the looks of it. If you follow those down. They appear to hook to the square bad at the bottom.

So where should I do as you said? Also the amp still powers up. When it does green light is on. It bumps the subs for a split sec as it goes into protect mode.

 

[Perry Babin]

It's not really important which two are connected by the trace. If two of the pots pads are connected together, connect all 3 together and power the amp up (all transistors clamped to the sink).

 

[2fast4u88]

O ok so for the pot that broke off connect all 3 prongs/pads together? If so what would you recommend to use to do so?

Also I'm not going to get a smoke show doing so am I? Should I also check for sounds output if the protection light goes off?

 

[Perry Babin]

Connect them together with a piece of wire (soldered between the pads).

This will not cause any problems. It's essentially like having the pot at one end of its rotation.

If the amp doesn't go into protect mode and you have the transistors clamped, check for audio.

 

[2fast4u88]

Ok cool I will give it a try in a few. Just making sure all 3 pads for the pot that broke off. Solder hook together as one. Just double checking.

 

[2fast4u88]

It works again I took the broken pot and soldered 3 wires to the itty prongs that was left. Then to the board. I then glue the pot upside down to the board for the time being. Plays just fine.

My ? is where can I get a pot or can I solder a wire across the pads or add resistors or something to have the bass boost like 3/4's or something along those lines. Thanks for the help

 

[Perry Babin]

If the pot is working, glued to the board and you don't want to try to find a replacement pot, you may as well leave it as it is. If you would be satisfied with a fixed resistor, this is no worse and a bit better because it's still adjustable.

 

[2fast4u88]

I am fine as long as it works but in case it don't could I use like a resistor for like 3/4's of the bass boost instead of full or would my only way to get some bass boost would be replace the pot with another.

 

[Perry Babin]

Set the pot to the position you want the bass set, desolder the pot and measure the resistance between the two terminals of the pot that are NOT connected by the trace. Install that value resistor between the two pads that are not connected by the trace.