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Old 7th September 2011, 10:13 AM   #1
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Default Super distorted old amplifier problem

This speaker is an old old one, about 10 years to 15 years i think.
Proton AM-455.
The problem is that when i fire up it in the morning, the one channel of the AMPLIFIER will sounds nothing like music, but like a rapping, zapping, super distorted sound, but it was based on the input (by hearing out the amplitude wave).
But the trick here is that the sound will go away after sometime, range from 1-10 minute. (I would be annoyed to death before i can wait for the beautiful from the amplifier)
It won't have that effect even after i use the amp after 1 hours of turning off amp. So i guess the factor here is the heat. (have experiment with hours of resting relation to the effect)

Is there any diagnosis for this problem ? or any specific bad component will cause this ?
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Old 9th September 2011, 08:44 PM   #2
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Possibles: Bad cap, broken or bad solder joint. Internal bonding wire failure in solid state device.

Check smaller local filter capacitors on bad channel side of amp. Also try getting a small non-conductive stick and GENTLY pushing in various spots on circuit board to perhaps locate a broken solder joint. Internal bonding wire failures can sometimes be located with canned circuit cooler spray. Use freeze spray sparingly spraying a quick shot right on any transistors. Keep as much as possible off circuit traces as moisture condensation will promote dendrite growth between traces (atoms from traces will electroplate themselves into microscopic conductive paths between the traces...no joke).
Wahl used to make a "hot spot" hot air blower that would heat one small area at a time to search for thermal intermittants. Which is what you're looking for, but large heat guns or hair dryers are kind of useless for such things as they heat too large an area. If you restrict their flow you can damage heat gun.
Best of luck
Doc
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Old 9th September 2011, 08:53 PM   #3
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Check the transistors best you can for shorts.
Replace all electrolytics regardless.
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Old 11th September 2011, 02:24 PM   #4
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haha, don't think is transistor shorting in all case. (well... it would either no sound, or overloading, and also result in dead amp)
thaumaturge : your advice was somewhat correct (related), I found in before you post, But i appreciate ! (hope found your post earlier)

The situation here is that it was the case of bad solder. the solder was too thin, as if its a "spider" in a speaker driver. If i were to apply some pressure to the bad solder component (to the side), i could see the legs follow the movement. In a proper solder, the legs should not move when the upper part is flexing.

My conclusion is that the solder was too thin at the beginning, so the current cannot go through much of it. the low current flowing capability cause rapid increase in temperature, result in expansion. This expansion cause increase in current carrying capability, thus allow full flow, then able the produce nice sound. This was imagination, but it is the possible case ?
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Old 11th September 2011, 02:32 PM   #5
Mooly is offline Mooly  United Kingdom
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You find the same in countless consumer products... tv's of a certain age particularly

Best to resolder the whole PCB if it's suspect.
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Old 11th September 2011, 03:07 PM   #6
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haha, mooly, thats the best yet tiring action, need to consider before do that, haha !
However , that happen to several small transistor on my amp, so after i resolder, the problem gone ! (been tested for about 5 days, no problem at all)
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Old 11th September 2011, 05:43 PM   #7
Mooly is offline Mooly  United Kingdom
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As a repair tech (back in the good old days lol) intermitent faults caused by dry joints and poor flow soldering were a huge problem. Although always nice to find the fault sometimes it made sense just to reflow all the whole chassis. 300 or 400 joints only takes around 5 to 10 minutes.

Something to beware of... some parts have oxidised leads and solder doesn't "take" well to the part, these then requiring a bit more time spending on them.
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Old 12th September 2011, 05:08 AM   #8
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haha, i think oxidised part is my problem here ,since i use alot of time to resolder (maybe my technique and skill of solder is weak ?)
How to solder 300 to 400 joint in 10 minutes ? thats insane fast ! (except for industrial method)
Maybe 30 to 40 joint in 5 minutes seems possible to me. ( it took me 15-20 minutes to resolder around 12 leg joint....
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Old 12th September 2011, 06:44 AM   #9
Mooly is offline Mooly  United Kingdom
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When it's the day job you get quick...
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Old 12th September 2011, 08:45 AM   #10
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haha, means its a life time acquire skill !
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