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Old 1st September 2010, 01:15 AM   #1
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Default Right channel not working in my amp

It's a Visonic NA-4300. It's at least 30 years old. The right channel fuse blew yesterday out of nowhere, it wasn't turned up loud or anything. I took the fuse from the left channel and put it in the right, and it still didn't work, but the fuse didn't blow. I tried the left speakers in the right channel and vice versa, all of the speakers were working fine in the left channel. There's a nasty electrical burning smell coming from it so I popped the top off to inspect for blown caps, burnt wires etc but nothing caught my eye. I'm not really that tech-savvy, so I probably overlooked something. Here's some pictures

Visonic NA-4300 - Imgur

I haven't looked at the underside of the pcb tray for fear of getting shocked. Do solid state amps hold a charge? Also, those two fuses on the pcb weren't blown.

I have a multimeter around here somewhere, though I don't know what to check, and what to check for.

Any and all help is greatly appreciated.
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Old 1st September 2010, 02:48 AM   #2
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In the third picture there are four white resistors. They connect to transistors on the heat sink at the bottom of the picture. Those transistors are probably your problem.
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Old 1st September 2010, 11:10 AM   #3
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none of the electrolytics that seen in the photo is expected to work ... they need to be replaced all of them ... for starts

any electrolytic that is involved in the signal path or secondary power supply units will result to some kind of unbalace and cause failure

here is some more information about repair procedures vintage amplifier repair/upgrade manual
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Old 1st September 2010, 11:19 PM   #4
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Thank you for your replies. I'll change the transistors and if that doesn't fix it I'll do a full work up on it
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Old 2nd September 2010, 03:38 AM   #5
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I pulled out one of the transistors and googled the codes on it and couldn't find anything. Does anyone know what they are and what I should replace them with?

http://imgur.com/EYqRz.jpg
http://imgur.com/iZjsV.jpg
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Old 2nd September 2010, 04:28 AM   #6
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Look here:
2SD428 datasheet pdf datenblatt - Toshiba Semiconductor - SILICON NPN TRIPLE DIFFUSED MESA TRANSISTOR ::: ALLDATASHEET :::

There are also more than one output transistor in this amp as they are always in a npn/pnp or push/pull config. What is the other numbers on the outputs? The big white resistors, emitter or ballast resistors need to be checked also the driver, pre drivers and other semiconductors all need to be checked. So, just to replace a few parts you may think might fix it may turn out to be a waist of time without the proper test equiptment and know how. There are lots of people on this site that can help you along. Formost you must have some level of basic test equiptment and without that you are on your way to a easter egg hunt, in the dark.
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Old 2nd September 2010, 04:45 AM   #7
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Also, Sakis is very correct on the caps, they will need to be changed due to age. The information he gave you for reading is formost and not a option. There are no short cuts to just get by in any repair. Write down all you results on paper, keep track of all you parts you selected to replace and evaluate the replacements with caution as all caps and transistors are not equal, all are made for a purpose and should be selected as such. Also do not move any adjustments on that board, they will be adjusted later under conditions outlined in the service manual and will not fix your problem. Do not buy any transistors from EBay. MCM, Mouser and B&D Enterprises are good choices to start with for orginal parts, and NO NTE subs for the transistors always try first to get the part installed by the OEM. Good luck and ask questions.
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Old 2nd September 2010, 04:57 AM   #8
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embrown has it right. There is much more to it than transistors.

D426 is short for 2SD426, the type number for an NPN transistor. Or is that 428?
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