Nikkai EAPA 450 car amplifier rear speaker output is a low level and distorts easily

[waigy]

One step forward two steps back.
I excitedly built it all back up, connected the speaker wires etc. into the car then drove about a mile to the nearest place I can turn up the volume without people hearing and it's much worse.
There's now something very wrong with the rear gain pot.
Just before soldering it back onto the board I measured the resistance and it was still working smoothly from zero up to 20.
But now, even with the rear rca inputs disconnected, if I turn the rear gain pot a tiny bit, the rear speakers crackle and start to move in and out.
With the rear right connected, it distorts much worse than it did before.
I can manage to get the rear left working quietly, but there's something wrong there too.
With the pot at minimum it also starts crackling and cutting in and out, but when I get up to halfway, it quietens down and starts from a low level then keeps getting louder till the maximum setting.
I'm at the point of giving up here.
I've already spent loads of time on this and it's an amp that's only worth a few quid when working properly.

[CapLeaker]

Either replace the pot or for sanity sake's put in a fixed resistor instead. That's why a oscilloscope is a must to make a project like this "easy work" out of it.

[waigy]

I found out the cause of all the crazy stuff the amp was doing.
After checking the resistance of the pot, but just before soldering it back into the board, I used pliers to make sure the metal tabs that hold the pot together were bent firmly back into position.
When I did that, I put a fine crack in the back plate of the pot.
I just checked the resistance again and it was going up to 200 then getting no reading.
Because I bought two car amps last night for £20, I'm past the point of considering this junk now so I just put one of the 100k pots for adjusting the high pass frequency in place of the rear gain.
I'll make sure I only turn it a small amount from minimum as it quickly gets up to 20k.
I'll give it one more chance and, if there's still any distortion in the right rear, it's time for a float test.

Throw it in my nearest river and see if it floats.

[redwire]

You can get a replacement pot instead of abandoning it. How many times can you tell a girl you've got a Clarion in the bedroom lol.

[waigy]

I tried the 100k pot and it still did the exact same thing making the speakers pulse slowly in and out and crackling etc., that was before even starting to turn the pot up, so it will be something else I have damaged on the board by taking it in and out a few times.
I had a couple of schoolboy errors when refitting the large heatsinks and saw sparks twice so that might have blown something else.
I just got myself another amp to add to the two I got last night (one of which was dead on arrival).
So I currently own 5 amps, with 2 not working, but the amps that are working are much better than the amp I've been trying to save so tomorrow I will be fitting them in the car.
I'm going to keep the dead amps for spare components, or float tests.
Thanks for all the help everyone.