My SU-8080 Technics is popping...

flambart · 3rd March 2011, 10:20 PM

Hi, I was listening my SU-8080 Technics, at mid/low volume, when it suddenly started popping and rustling on the left channel.

The noise was really loud, and I've seen the woofer moving very slowly backward and forward. After few seconds, the protection circuitry has cut the signal, so I have to imagine that the unwanted DC current was seriously high.

I've isolated the pre-amp, and I've realized that the problem is limited to the power section, left channel.

This malfunction happened again 2-3 times, in totally unpredictable manner: after a variable time (seconds, or minutes), the noise disappears exactly as it came

Someone other encountered the same problem ? Old electrolytic caps could be the reason, and which ones ? Otherwise, any alternative idea about?

Thank you to everyone in advance , Paolo

ostripper · 4th March 2011, 07:39 AM

Looks like a good old discrete "masterpiece".

"popping/rustling" is usually a semi with a bad junction. The large devices (on the heatsinks) would just quickly blow the fuse . This leaves the small devices in the voltage stage. Before you get the noise , get a can of freeze spray ready ... spray 1 device at a time until the noise stops ... that is the most likely one. Bad Caps will "bulge" and hum will increase , offset will change , or they will just smoke/explode. The random nature of the problem sounds like a small signal device. (had several I repaired do this )

OS

flambart · 6th March 2011, 08:55 PM

Thanx so much for your kind reply.

The strange thing: the last time the problem happened (yesterday) at the very first start, that means with amp & components totally cold.

After few seconds of pops, the amp has kept playing all the day long, with no more problems at all.

I agree with you thinking about small signal transistors: have I to replace all ?

ostripper · 7th March 2011, 12:53 AM

Clean potentiometers , and keep that can of freeze spray on top.

Intermittent's suck.

OS

smartx21 · 7th March 2011, 12:43 PM

Bad solder joint?
Quality control on name brand electronics | yProxy? Blog

kapwinnnng · 30th May 2011, 03:00 AM

Quote:

Originally Posted by ostripper

Clean potentiometers , and keep that can of freeze spray on top.

Intermittent's suck.

OS

How would one go about cleaning the potentiometers? Just some contact cleaner spray or is it more involved?

sakis · 13th December 2011, 12:47 PM

all capacitors need to be replaced in such aged unit .... half of the problems might be self cured after that

flambart · 25th December 2011, 06:01 PM

During the last wednesday, after months of total oblivion, I've given another chance to my amp...
Well, there was this damn TR301 (a 2SA798A, two PNPs in one 5 pin case) very sensitive to the freeze spray.
I've replaced it, using 2 twin 2SA798 transistors (the original code is not available anymore), and everything sounds nice now!

Thanks a lot to everyone gave me a helping hand

Merry Christmas and Happy New Year to everybody!

Ciao, Paolo

3rd March 2011, 10:20 PM	#1
flambart diyAudio Member Join Date: Sep 2009	My SU-8080 Technics is popping... Hi, I was listening my SU-8080 Technics, at mid/low volume, when it suddenly started popping and rustling on the left channel. The noise was really loud, and I've seen the woofer moving very slowly backward and forward. After few seconds, the protection circuitry has cut the signal, so I have to imagine that the unwanted DC current was seriously high. I've isolated the pre-amp, and I've realized that the problem is limited to the power section, left channel. This malfunction happened again 2-3 times, in totally unpredictable manner: after a variable time (seconds, or minutes), the noise disappears exactly as it came Someone other encountered the same problem ? Old electrolytic caps could be the reason, and which ones ? Otherwise, any alternative idea about? Thank you to everyone in advance , Paolo

4th March 2011, 07:39 AM	#2
ostripper diyAudio Member Join Date: May 2008 Location: Albany , NY (smallbany)	Looks like a good old discrete "masterpiece". "popping/rustling" is usually a semi with a bad junction. The large devices (on the heatsinks) would just quickly blow the fuse . This leaves the small devices in the voltage stage. Before you get the noise , get a can of freeze spray ready ... spray 1 device at a time until the noise stops ... that is the most likely one. Bad Caps will "bulge" and hum will increase , offset will change , or they will just smoke/explode. The random nature of the problem sounds like a small signal device. (had several I repaired do this ) OS __________________ Mongrel website , always current and updated : http://67.248.209.21/D%3A/WEBSITE/

7th March 2011, 12:53 AM	#4
ostripper diyAudio Member Join Date: May 2008 Location: Albany , NY (smallbany)	Clean potentiometers , and keep that can of freeze spray on top. Intermittent's suck. OS __________________ Mongrel website , always current and updated : http://67.248.209.21/D%3A/WEBSITE/

7th March 2011, 12:43 PM	#5
smartx21 diyAudio Member Join Date: Mar 2010 Location: Santiago, RS/ Brasil	Bad solder joint? Quality control on name brand electronics \| yProxy? Blog __________________ We should not dwell on what we do not have, but, instead, be grateful for what we do have!

13th December 2011, 12:47 PM	#7
sakis diyAudio Member Join Date: Jan 2006 Location: nea makri athens greece	all capacitors need to be replaced in such aged unit .... half of the problems might be self cured after that __________________ SERVICE ΙΑΠΩΝΙΚΩΝ ΜΗΧΑΝΗΜΑΤΩΝ ΗΧΟΥ www.eastelectronics.gr


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6th March 2011, 08:55 PM	#3
flambart diyAudio Member Join Date: Sep 2009	Thanx so much for your kind reply. The strange thing: the last time the problem happened (yesterday) at the very first start, that means with amp & components totally cold. After few seconds of pops, the amp has kept playing all the day long, with no more problems at all. I agree with you thinking about small signal transistors: have I to replace all ?

25th December 2011, 06:01 PM	#8
flambart diyAudio Member Join Date: Sep 2009	Finally I've got it ! During the last wednesday, after months of total oblivion, I've given another chance to my amp... Well, there was this damn TR301 (a 2SA798A, two PNPs in one 5 pin case) very sensitive to the freeze spray. I've replaced it, using 2 twin 2SA798 transistors (the original code is not available anymore), and everything sounds nice now! Thanks a lot to everyone gave me a helping hand Merry Christmas and Happy New Year to everybody! Ciao, Paolo

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