Help repairing Akai AM-M939

[avionic]

TR901b
https://www.bdent.com/nsearch.html?catalog=yhst-864421581610834172249761&query=2SC3964
D3b --- HZ6LA1 ---> 5.2v - 5.5v /500mw
Exact replacement.
https://www.mouser.com/ProductDetail/Nexperia/NZX5V6A133?qs=/ha2pyFadui8KnG60%2baPS6sWliVLjkH/1UZqr01DfAN6AWy11Yfolw==

 

[tallman5353]

I've reversed 901b with 901 just to test, all measurements are still identical. I'll swap out the zener and see what happens.

 

[tallman5353]

Don't currently have any on me, the closest i can find that I can pickup easily is this:
5.1V 1N4733 1 Watt Zener Diode https://www.jaycar.com.au/5-1v-1n4733-1-watt-zener-diode/p/ZR1403. There is also a 5.6v version.

Will that suffice?

 

[petehall347]

Voltage Tolerance:
3 %

 

[avionic]

Don't currently have any on me, the closest i can find that I can pickup easily is this:
5.1V 1N4733 1 Watt Zener Diode https://www.jaycar.com.au/5-1v-1n4733-1-watt-zener-diode/p/ZR1403. There is also a 5.6v version.

Will that suffice?

You can give it a try.

 

[tallman5353]

Ok, i think that did the trick!
Right channel is now distortion free! I am also getting correct idle current readings on right channel.

I have noticed the left channel is a little louder however when playing music.

I might swap out the other D3 with the same replacment to see if it balances out

 

[avionic]

 

[tallman5353]

Swapped it out, however there still is more volume and definition on the left channel. Any guesses to what transistors/components to replace?
By the way, thanks so much for all of your help so far!

 

[petehall347]

try swapping speakers first .

 

[avionic]

Probably wouldn't hurt to give all the switches and controls a little Deox-it love.

 

[tallman5353]

Swapped speakers, deoxit-ed all swtiches and pots. Same channel is still quieter. What other component could be causing it?

 

[avionic]

Does speaker B sound the same as speaker A?

 

[avionic]

Does this unit have pre-out and main-in jacks on the rear panel?

 

[tallman5353]

Yeah a and b sound the same.
Have tried tone bypass and direct couple (bypassing pre in/out jacks). Same issue

 

[avionic]

Yeah a and b sound the same.
Have tried tone bypass and direct couple (bypassing pre in/out jacks). Same issue

How about by-passing the L pre-out to the R main-in and R pre-out to the L main-in?

 

[tallman5353]

Ok, just tried that. Right speaker is still lower. I guess that means the power amp side is the issue?

 

[petehall347]

good guess .

 

[avionic]

Ok, just tried that. Right speaker is still lower. I guess that means the power amp side is the issue?

Thats a pretty good bet.

 

[avionic]

Whats the collector rail voltages on your output transistor? Compared to the other channel?

 

[tallman5353]

Collector voltage is 52v on all power transistors