Very low volume on Sub

[mikay786]

Working on this Monitor Audio Radius 360 sub that I got for nowt.

It powers on and receives a signal but it barely produces any sound, I can just about feel the driver beating when I put my hand to it.

Have tested all electrolytic caps and they are not too bad, changed a couple. Tested most transistors and seem ok aside from a couple that were reading slightly different to the others so replaced with new ones matching the others readings.

Got one more transistor out but not sure what the readings mean and don't have anything to compare it too.

Reads on transister tester as a BJT-NPN

MPSA13
hFE = 47.7k
Vf = 1.19v

is that normal?

Next I'm going to check the C5198 & A1941

[budm]

Re: Very low volume on Sub

Check the 20K Dual Volume pots for open circuit.
It uses cheap pots for such an expensive sub-woofer.
http://s807.photobucket.com/user/bud...?sort=3&page=1

[mikay786]

Re: Very low volume on Sub

Just about to remove it from board, how do I test it?

[budm]

Re: Very low volume on Sub

Just check the resistance between the wiper (center pin) and each pin end as you rotate the shaft, also between end pins.

[mikay786]

Re: Very low volume on Sub

I think one of the pots is bad as is reading a bit funny

On good pot it reads

Pin 1-2 Variable depending on dial position, 3 Ohm up to 20k
Pin 2-3 Variable from 20k to 45 Ohm
Pin 1-3 20k Constant

Pin 4-5 Variable depending on dial position, 3 Ohm up to 20k
Pin 4-6 20k Constant

On suspected pot

Pin 2-3 all over the place, M ohms
Pin 4-5 variable from 46 Ohm to 20k
Pin 4-6 is 0.L
Pin 5-6 is 0.L

[mikay786]

Re: Very low volume on Sub

What is the official name for right angle pin pots?

http://www.ebay.co.uk/itm/DP-20K-Lin...4AAOSwT6pVkTEn

Found tehse but the pins a straight

[budm]

Re: Very low volume on Sub

I forget the manufacturer of the pot, it is on the back or the side of the pot.

It is called Vertical mount with body support mounting tabs.
I.E.:
http://www.britishaudioservice.com/#...iometers/c15gn You can try contacting them.
http://www.globalsources.com/gsol/I/...htm#1130293798

[rhomanski]

Re: Very low volume on Sub

Why don't you just clean the pot with Caig deoxit D5 and test again? I usually clean things 3 times giving it 24 hours between cleans. Fixes 40 year old pots, some I did 8 years ago and they still work perfect.

[budm]

Re: Very low volume on Sub

What I found wrong with the pot were bad contacts between the eye rivet of the terminal to the carbon trace on the the phenolic substrate, I tried recrimping it with long nose plier without permanent success.
You can easily move those terminals, they are just cheaply made pots.
BTW, it is dual-pot but only one pot is being used.

[stj]

Re: Very low volume on Sub

i think the track is open-circuit at one end - cleaning wont help
i also think it should be log type, not linear for volume.

[stj]

Re: Very low volume on Sub

does this device use the pot's threaded shaft and a nut to fix on the backplate, or is it just the pcb mounts used?

because:
http://www.rapidonline.com/omeg-2gec...ontrol-65-1444
and some short wires would work if it's fixed

[budm]

Re: Very low volume on Sub

I used the single pot for the replacement (it only uses one of the two-gang pots), soldered 5 small solid wires to the 3 terminals, and two 16AWG solid wires to the side of the body for the mounting support as original and to set it at the correct height.

[mikay786]

Re: Very low volume on Sub

Why don't you just clean the pot with Caig deoxit D5 and test again? I usually clean things 3 times giving it 24 hours between cleans. Fixes 40 year old pots, some I did 8 years ago and they still work perfect.

Tried with switch cleaner to no avail.

What I found wrong with the pot were bad contacts between the eye rivet of the terminal to the carbon trace on the the phenolic substrate, I tried recrimping it with long nose plier without permanent success.
You can easily move those terminals, they are just cheaply made pots.
BTW, it is dual-pot but only one pot is being used.

They look pretty tight on mine, no pins that I would say are loose.

does this device use the pot's threaded shaft and a nut to fix on the backplate, or is it just the pcb mounts used?

Uses both a nut on the shaft and like wedges on the underside of the base that are soldered to the board.


Ive ordered the ones from eBay as have used them before on another MA sub that I broke the pot on not knowing there was a nut!

I just cut off the legs from the old one, soldered the top legs on to the top 3 pins and bent the bottom 3 pins over to get it to fit.

[mikay786]

Re: Very low volume on Sub

Thanks budm / stj again, all sorted.

[budm]

Re: Very low volume on Sub

Glad to hear that it is fixed.