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Electronics => Repair => Topic started by: EvilGeniusSkis on September 21, 2015, 07:18:27 pm

Title: Pioneer A30 stereo amp repair
Post by: EvilGeniusSkis on September 21, 2015, 07:18:27 pm
I am repairing a pioneer A30 amp that failed. I have diagnosed the problem as bad main amplifying transistors(2 each: 2SA1265N and 2SC3182)  and have new ones on order from amazon as I could't find them anywhere else.  The transistors are not electrically connected to the heat-sink, however, instead of using sil-pads they used some sort of non-conductive  thermal paste. I really have no clue how to find this, so I thought of using sil-pads but couldn't find any for a reasonable price (could only find them in manufacturing quantities). does anyone know where to find non-conductive thermal paste?
(https://pbs.twimg.com/media/CPcwVY-UAAAIQOQ.jpg:large)

url for transistor purchase http://www.amazon.com/2SA1265N-2SC3182-140V-100W-TOSHIBA/dp/B012RYUG50/ref=sr_1_1?s=industrial&ie=UTF8&qid=1442787363&sr=1-1&keywords=2sc3182n (http://www.amazon.com/2SA1265N-2SC3182-140V-100W-TOSHIBA/dp/B012RYUG50/ref=sr_1_1?s=industrial&ie=UTF8&qid=1442787363&sr=1-1&keywords=2sc3182n)
Title: Re: Pioneer A30 stereo amp repair
Post by: tautech on September 21, 2015, 07:34:50 pm
More likely they are insulated package devices.  :-//
If so any heatsinking thermal paste wil do.
Title: Re: Pioneer A30 stereo amp repair
Post by: EvilGeniusSkis on September 21, 2015, 07:43:06 pm
center pin is connected to the back. back is not connected to heat-sink
Title: Re: Pioneer A30 stereo amp repair
Post by: tautech on September 21, 2015, 07:58:23 pm
center pin is connected to the back. back is not connected to heat-sink
Mica washers?
Title: Re: Pioneer A30 stereo amp repair
Post by: David_AVD on September 21, 2015, 09:45:09 pm
+1 for the mica insulator.  They are very thin and not always seen until you remove the transistor.

I've never heard of relying on the heat transfer compound to electrically insulate a device.
Title: Re: Pioneer A30 stereo amp repair
Post by: singapol on September 22, 2015, 06:25:21 am
center pin is connected to the back. back is not connected to heat-sink

By the looks of it, 2SC3182 is not an insulated device,look carfully there should be transparent mica insulator ( they may break or separate easily). You should be able to buy small diy qty. from Digikey,Mouser,etc in addition to heatsink compound/paste.

http://datasheet.eeworld.com.cn/pdf/SAVANTIC/266920_2SC3182N.pdf (http://datasheet.eeworld.com.cn/pdf/SAVANTIC/266920_2SC3182N.pdf)
Title: Re: Pioneer A30 stereo amp repair
Post by: pinyoro on September 23, 2015, 08:22:17 pm
Have you checked the driver transistors as they are probably short circuit collector to emitter. While the output transistors (the ones you are identified as faulty) are out you could check the Base to emitter voltages going to each output transistor on the pcb. The voltage should be around 0.6 volts. Also check to see whether the emitter resistors usually around 0.47 ohms are not open circuit. If you replace the transistors without thoroughly checking you'll blow the new transistors. Usually it is not only the power transistors that fail.
 
Title: Re: Pioneer A30 stereo amp repair
Post by: EvilGeniusSkis on October 17, 2015, 10:24:45 pm
I just checked and there are mica insulator which btw are the size of the white rectangle in the picture.

I tried checking surrounding components like pinyoro suggested however I had trouble following the traces due to a large number of jumper links. I couldn't find the correct repair manual online to help withe tracing the parts oust either.
Title: Re: Pioneer A30 stereo amp repair
Post by: BurningTantalum on October 18, 2015, 06:42:00 am
Don't forget to check if any replacement device(s) need a 'top hat' plastic insulator under the mounting screw, as well as the mica washer.
BT
Title: Re: Pioneer A30 stereo amp repair
Post by: dom0 on October 18, 2015, 09:31:56 am
Don't forget to check if any replacement device(s) need a 'top hat' plastic insulator under the mounting screw, as well as the mica washer.
BT

These look like TO-247 (or a variant) which are designed so as to not need an additional plastic screw insulator.
Title: Re: Pioneer A30 stereo amp repair
Post by: EvilGeniusSkis on October 19, 2015, 09:37:29 pm
Don't forget to check if any replacement device(s) need a 'top hat' plastic insulator under the mounting screw, as well as the mica washer.
BT

These look like TO-247 (or a variant) which are designed so as to not need an additional plastic screw insulator.
You are correct these transistors don't need the insulator bushing
Title: Re: Pioneer A30 stereo amp repair
Post by: EvilGeniusSkis on October 22, 2015, 05:07:14 pm
Seeing as this amp has a metal case, would it a good idea to replace the 2 prong cord with a 3 prong one?
Title: Re: Pioneer A30 stereo amp repair
Post by: envisionelec on October 26, 2015, 10:18:54 pm
Just an FYI - those Toshiba parts linked to Amazon are terrible fakes.

In fact, Toshiba has not made these devices for many years. A good replacement for them are the FJA4210 and FJA4310 from Fairchild.

Other possiblities:

2SC3182: BD 245D, 2SC2706, 2SC2837, 2SD1047
2SA1265: BD 246D, 2SA1146, 2SA1186, 2SA1227(A)
Title: Re: Pioneer A30 stereo amp repair
Post by: envisionelec on October 26, 2015, 10:26:28 pm
Don't forget to check if any replacement device(s) need a 'top hat' plastic insulator under the mounting screw, as well as the mica washer.
BT

These look like TO-247 (or a variant) which are designed so as to not need an additional plastic screw insulator.

The originals are TO-3P - different lead spacing and different pin location from the heatsink surface. Replacing a TO-3P with a TO-247P is not recommended.