Marantz 2225 one channel low

[goldswimmerb]

Hey guys, so I've been bitten by the repair bug and figured I would try my hand at a 2225. I've been going through it and think I've finally almost found my culprit.

The left channel comes out much quieter than the right and when turned all the way up sounds terribly distorted. All voltages on the main amp board checked out so I moved my focus to the preamplifier.

Here's where I am at, the right channel voltages all seem to be normal, the left channel has some abnormalities. I noticed that at HE03 I was getting E:0V C:.2V and B:7.7V

I then lose the circuit there. I swapped out the 2sc1328s for KSA1845S and that made no difference. I also went through and just replaced the capacitors and reflowed every single solder joint, also to no avail.

Anyone have any ideas what could be causing this? I'm thinking a shorted 2SA722 but I'm honestly not sure.

 

[goldswimmerb]

RE15 gets really hot, measured it with a DMM and found it has 18v across it...

 

[catrafter]

My first guesses would be HE03 or CE03 shorted.

Tom

 

[goldswimmerb]

My first guesses would be HE03 or CE03 shorted.

Tom

Yup, found it. Accidentally shorted CE03.

Now to figure out why the left channel distorts much more than the right. they're both at the same volume now but it sounds like the mid-range on the left channel is distorting. Anything I should check or any problematic diodes or transistors in these models?

 

[goldswimmerb]

Also the AM tuner isn't working at all now. Where should I check for power on that?

 

[goldswimmerb]

FM works perfectly fine though, which is strange

 

[catrafter]

I'd look for a broken wire from the AM loopstick antenna first.

Tom

 

[goldswimmerb]

I'd look for a broken wire from the AM loopstick antenna first.

Tom

Also the 2225 will not bias on the left channel without a load attached, the other channel works fine, any ideas where to look for the culprit? I get 5mv max bias with no load and with a load it biases fine...

 

[goldswimmerb]

I'd look for a broken wire from the AM loopstick antenna first.

Tom

Alright, so when I run signal through the amp im im see DC in relation to volume on pin J712, would this be a sign of just a leaky transistor or something more dubious?

 

[goldswimmerb]

Just tested with a new set of outputs from my spare transistor pile (some compatible OnSemis, still have the same issue...) Hmmmm

 

[goldswimmerb]

I went and replaced the small signal diodes, most resistors and all the transistors on my trouble channel. Still no dice... After messing around for a bit I noticed the outputs in the channel don't bias unless they have a load across the speaker terminals. As I increase the volume the distortion worsens and pin J712 has DC ranging from 1V while idle to 7+V at higher volumes, the outputs get fairly warm too. Anyone have any ideas? I'm at the point where I may just board swap...

 

[petehall347]

check emitter resistor values just in case its something simple .