Sugden a21a power amp repair

adamus · 24th June 2008, 07:24 PM

I have a sugden power amp. It is loosing its left channel intermittantly once warmed up. For the first 2 mins its fine, then it starts loosing and regaining the left channel.

Anyone got any ideas of where to start? I checked the input wiring and joints - its fine.

Jan Dupont · 25th June 2008, 03:10 AM

According to your description it's most likely a bad solder joint, as it happens when the amp warms up............

adamus · 25th June 2008, 06:35 AM

that was my thought. Time for some checking.

Mooly · 25th June 2008, 03:37 PM

What vintage is it out of interest.

adamus · 25th June 2008, 09:16 PM

i am not sure. ITs a black poweramp, with a horrible yellow 'neon' switch. a21a. Looks latte 80's. I checked the caps, they all seem fine (nothing dry etc). time to looks at joints. the sound distorts pre cutting out. could this potentially be bad output trannies, i know sugden bias the hell out of them.

poynton · 25th June 2008, 10:10 PM

Quote:

Originally posted by adamus
i am not sure. ITs a black poweramp, with a horrible yellow 'neon' switch. a21a. Looks latte 80's. I checked the caps, they all seem fine (nothing dry etc). time to looks at joints. the sound distorts pre cutting out. could this potentially be bad output trannies, i know sugden bias the hell out of them.

Probably right at the front end.
If it was in the power section, something would have blown !!

Sounds like one of the supply rails in dropping out.

Andy

Mooly · 26th June 2008, 06:56 AM

Do you have a meter etc. You are going to have to take some measurements, possible comparing left/right. The output midpoint is as good a place as any to measure first as any power amp problem will probably show up here first.
Does it seem heat related, going duff after say 30 mins from cold.
Is the speaker output AC coupled on this one --- single rail supply.
When it goes faulty is it "tapable" if you poke the PCB with it on.
When it goes faulty does it stay that way until you switch off.

adamus · 26th June 2008, 02:00 PM

its must be heat related. Its fine for 2-3 mins, then left channel goes slightly fuzzy / crackles, then drops, then returns intermitantly.

Nothing looks burned. No bulging caps. Anyone know where i can get a schematic?

adamus · 26th June 2008, 02:00 PM

Think i have fixed it!!!

Bad solder joint on the left out channel on the relay board. Reflowed adn fingers crossed i have enjoyed 10 minutes of music.

Coud be fluke though, will have to leave it running for a bit.

adamus · 26th June 2008, 02:00 PM

30 mins in and it is still playing sweet music.

Think i have sorted it. Thank the lord for the 'tap test'.

24th June 2008, 07:24 PM	#1
adamus diyAudio Member Join Date: Apr 2008	Sugden a21a power amp repair I have a sugden power amp. It is loosing its left channel intermittantly once warmed up. For the first 2 mins its fine, then it starts loosing and regaining the left channel. Anyone got any ideas of where to start? I checked the input wiring and joints - its fine.

25th June 2008, 03:10 AM	#2
Jan Dupont diyAudio Member Join Date: Apr 2003 Location: Copenhagen, Denmark	According to your description it's most likely a bad solder joint, as it happens when the amp warms up............ __________________ Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com

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25th June 2008, 06:35 AM	#3
adamus diyAudio Member Join Date: Apr 2008	that was my thought. Time for some checking.

25th June 2008, 03:37 PM	#4
Mooly diyAudio Member Join Date: Sep 2007	What vintage is it out of interest.

25th June 2008, 09:16 PM	#5
adamus diyAudio Member Join Date: Apr 2008	i am not sure. ITs a black poweramp, with a horrible yellow 'neon' switch. a21a. Looks latte 80's. I checked the caps, they all seem fine (nothing dry etc). time to looks at joints. the sound distorts pre cutting out. could this potentially be bad output trannies, i know sugden bias the hell out of them.

26th June 2008, 06:56 AM	#7
Mooly diyAudio Member Join Date: Sep 2007	Do you have a meter etc. You are going to have to take some measurements, possible comparing left/right. The output midpoint is as good a place as any to measure first as any power amp problem will probably show up here first. Does it seem heat related, going duff after say 30 mins from cold. Is the speaker output AC coupled on this one --- single rail supply. When it goes faulty is it "tapable" if you poke the PCB with it on. When it goes faulty does it stay that way until you switch off.

26th June 2008, 02:00 PM	#8
adamus diyAudio Member Join Date: Apr 2008	its must be heat related. Its fine for 2-3 mins, then left channel goes slightly fuzzy / crackles, then drops, then returns intermitantly. Nothing looks burned. No bulging caps. Anyone know where i can get a schematic?

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