Yamaha A 1020 in protection

[Dallas]

Hello everyone, I have recently gotten a bit nostalgic about the stereo equipment I grew up on and have aquired a Yamaha CA 610 II amp and CT 810 tuner (both working), a Nakamichi RX 202 Tape deck (needs a little help) and a Denon DP 47f TT (Working). I Purchased a Yamaha A 1020 Amp that turned out to be DOA and I also have a Yamaha CA 1000 that needs help. I am interested in learning how to repair these units. I have started reading an eloctronics book and I have a fluke DMM, Tektronix 466 100 mhz oscilloscope and I have made a dim bulb tester. I am currently focusing on the Yamaha A 1020 Amp, I found 4 bad transistors, all on one side of the heatsink, 2 npn and 2 pnp. I replaced these transistors with the same part number toshiba transistors. I used the dim bulb tester (checked it using a working amp) and after a few seconds the light did not dim so I removed power. I rechecked the transistors and they still appear to be good. I guess I should mention that when I received the amp the power light came on but no sound from speakers. The relay did not pull in and a bank of resistors was generating alot of heat, also the fuses still show continuity. I have downloaded a service manual for this unit. Any help would be greatly appreciated

 

[merrylander]

Have you checked the driver transistors, the ones under the clamp on the heatsink? Also whe outputs blow they sometimes take the emitter resistors out as well, the big rectangular white ones.

 

[Dallas]

Thanks for the help. I found one bad A1306 PNP transistor, shorted
between base and collector. The resistors checked out ok. I checked online for a
2SA1306 transistor, digikey and MCM do not carry this item. I found some at Pacific Semiconductors USA and also at Electronix corp. I have heard that some companies sell inferior electronic parts and was wondering if you might know of the reputation of either of these companies.

 

[ryuuoh]

I've dealt with B&D enterprises, they are reputable.
http://www.bdent.com/search/search.jsp?contains=2SA1306&category=ALL&submit.search=Search!

 

[smokeetheamp]

yes i am haveing the same problem with a-1020 powers on no output,my uncle is a great tech but is not into the internet,i myself am haveing a hard time finding the service manual & any help would be great.thanks

 

[avionic]

yes i am haveing the same problem with a-1020 powers on no output,my uncle is a great tech but is not into the internet,i myself am haveing a hard time finding the service manual & any help would be great.thanks

Shoot Mike and e-mail I'm sure he can hook you up.

mike@vintageaudiomanuals.com

 

[olo111]

When output transistors blow, You should also check protection circuit: TR231, TR232, TR233, TR234 and diodes D212, D213. This is common fault for A1020.

 

[Dallas]

I have a question about the mica insulators for the output transistors. I purchased some TO-220 insulators but they do not fully cover the back of the transistor. Perhaps they sent me the wrong size, any input would be helpful. Also can the transistors and diodes mentioned in the above post be checked in circuit?

 

[megawatt]

I have a question about the mica insulators for the output transistors. I purchased some TO-220 insulators but they do not fully cover the back of the transistor. Perhaps they sent me the wrong size, any input would be helpful. Also can the transistors and diodes mentioned in the above post be checked in circuit?

the transistor in the image does not look like a to-220. Looks more like a
to-247 or 246, or something like that .

to-220 have a little metal tab extending over the top or the case.

check this image (click on to to supersize)
http://www.siongboon.com/projects/2006-06-19_switch/rs transistor package.jpg

 

[olo111]

Your mica is to small, the output devices are in the TO-247 package.
Yes, You can check transistors in circuit.

 

[Dallas]

Thanks for the input, I checked the diodes D212, D213 and they checked out ok. I am not certian what kind of readings I should be getting on the transistors TR231, TR232, TR233, TR234. I posted a pic of the transistors in question and I wish to know what readings I should expect using the flat side of the transistor as a reference. I believe with the flat side facing me it should be E C B. Also I cannot seem to find mica TO-247 insulators at a reasonable cost, however I did fing some Kapton insulators on ebay, item #380166836383, Would these be an acceptable substitute for mica?

 

[OverLoad]

Your mica is to small, the output devices are in the TO-247 package.
Yes, You can check transistors in circuit.

Actually no they aren't. They are TO-3P(N) cases also known as MT-100.

Also I cannot seem to find mica TO-247 insulators at a reasonable cost, however I did fing some Kapton insulators on ebay, item #380166836383, Would these be an acceptable substitute for mica?

Actually you want TO-3P insulators. Very easy to find and inexpensive so take your pick Silicone or Mica. Personally I prefer mica and heatsink compound.

 

[Dallas]

Here are the readings I am getting with my fluke 8025A using diode check. I am reading these using the flat side of the transistor facing me and the leads downward, I believe the order should be ECB

transistor type: 2SA970 PNP

TR231 TR233
E pos, B neg 0.559 0.557
B neg, C pos 0.553 0.539
E neg, B pos 0.813 1.52
B pos, C neg OL 1.86

Transistor type 2SC2240 NPN

TR232 TR234
E neg, B pos 0.617 0.528
B pos, C neg 0.613 0.542
E pos, B neg OL 0.607
B neg, C pos OL 1.844

 

[OverLoad]

For the transistors in question you should only be measuring a diode drop from B to E junction and B to C junction forward biased (NPN= pos lead on base & PNP= neg lead on base). Reverse biased (NPN=neg lead on base & PNP=pos lead on base) B to E and B to C should read open. You also need to check E to C which you haven't done. If the transistors are still in circuit all bets are off. The only reliable way is to measure out of circuit.