NEC Transistor? b965 / d1288 - 70W System

[Morbid]

Hi i have an aiwa mx-70 amp not working i've got from a freind and the power transistors might have burned.
the transistors is B965 / D1288
i guess one is PNP and the other is NPN
i dont know what repleace can i use
or what to do ....when i plugged the amp smoke came out of their zone...

a stereo driver must be with pairs and i only see one pair...
whats going on?!

thanks!

 

[Morbid]

 

[sajti]

2SB365/2SD1288 120V/7A/70W complementary BJTs, made by NEC. Try to find something which has same specifications.

sajti

 

[Morbid]

Thanks, these are the same transistors i mentioned?
i've checked the voltage on the transistors and what i've got is:

b965 : CENTER : -72V -> PNP?
d1288: center: + 72V -> NPN?

and i need to know base,emmiter and collector.

when i checked one transistor all his legs were shorted..

 

[Enzo]

Look at the transistor with the legs pointing down. Print side facing you. Now left to right B-C-E.

If one has shorted, there will be same smaller transistors associated with these. They are the drivers. Follow the trace from the Base of the output transistor and it will go to what I am talking about. Check these driver transistors as well.

Look at the resistors asociated with this circuit. Some may have burned open when the amp failed.

 

[Morbid]

ok i will check that and i've found one pair of these transistors at Kinser, if i will put only one pair only one side of the amp will work?

i saw that the other pair was missing (maybe from repair or someone took them off)

if i will fix one side it will be ok? (for meanwhile to check)

 

[Morbid]

its been a while
can i still fix only one side to work meanwhile?

(replace one pair of the Drivers instead of 2)
for mono instead of stereo?

 

[Tom4F]

Hello from Czech Republic,

I have broken AIWA MX-70.

At first I found broken tranzistor B965, so I am starting to find something to replace it.

Have you more info, or scheme of MX-70 amplifier?

Thak you.

Tomas

 

[Giaime]

No: don't try to fix only one channel of it. The broken one might, under some circumstances, continue to self-destruct. In an amp always repair everything BEFORE you turn it up. Or the magic smoke...
For example, since at idle the amplifier sees only half the current in the output devices, it might raise its rails voltage and drive the remaining outputs on stress, but they might survive. But a little driver connected to them wouldn't....

For that transistor replacement, if they are in T03 case (the metal one with 2 legs under it) either get MJ15003 and its PNP complement (don't remember the number), or use a cheaper 2N3442... there are many that would do the job.

It is critical that you check EVERY transistor of the power amp, and also every power resistor. Once I get a 5W 0.24ohm resistor that was very clean outside, no signs of burns, but it measured 50kohm...