Harman Kardon AVR 20II Repair (pics)

[Alex2507]

Just in case Google stopped servicing the east coast D):

Lol! What an opportunist! Remind me to never bend over to tie my shoe in front of you.

Yeah, I don't know what that means in terms of looking at the circuitry, just that the stages won't have a capacitor between them. That's why I buy stuff that works.

I got stuff that works ... most of time.

Part of this is understanding amplifiers ... which I don't ... yet. I mean, if I wasn't out of my depth it wouldn't be any fun. The trick with this would be to be able to look at a schematic and just know. Stuff like this takes me time, lots of time. I know more than more than most anybody in the real world but this forum affords me the pleasure of talking to some very knowledgeable folks. (not you) lol! j/k

 

[highfigh]

Yes, but when you test them with a multimeter it will read the voltage drop of the diode, so yes it will read about .6v depending on the diode.

Out of circuit, it's measuring continuity, which as we all know, is Ohms. Measuring voltage requires a voltage source, which a volt meter isn't.

 

[Haoleb]

Out of circuit, it's measuring continuity, which as we all know, is Ohms. Measuring voltage requires a voltage source, which a volt meter isn't.

Perhaps you're not understanding me here, Using every DMM i have ever used, on the diode function it will display the voltage drop through the diode. Which is why I said it should likely read something such as .6v

 

[Rickster71]

Yesterday I got this for $20. Plugging it in turned the power button red.
Pressing power button turned it green for a few seconds. Then back to red.
A fuse labeled NB5A125V (short glass job) is blown.
Two resistors have leads that either corroded or burned off.
No burn marks but there was a green/white dust covering the area.
They are on a PCB attached to the volume control.
A link to a real service manual and a color code translation would help.
Pic's as promised. Thanks for stopping by.

Hey Alex, since the top of the board looks like something was spilled on it, and there's that corrosion.
It makes me wonder what the solder side of the board looks like.
That looks like it was powered up when it got wet.

Since it's a single sided board it only has solder on the bottom. So when it got wet, the liquid just sat and pooled in the holes where the component leads go, and really corroded the solder joints.

As a comparison, a double sided board would have a copper land on both sides of the board. So when the board was wave soldered, the molten solder would come up through the hole and fill it completely.

 

[Adam]

Let me see if I translate for you, Rick. "Alex, that receiver is fried." (My family-friendly translation.)

Did I get that right?

EDIT: Don't let it stop you, though, Alex. Another $200-$300 on that bad boy, and it'll look great. Probably still won't work, but dang it'll be shiny. (J/K, man. I'm impressed that you're working on it like you are.)

 

[Rickster71]

Let me see if I translate for you, Rick. "Alex, that receiver is fried." (My family-friendly translation.)

Did I get that right?

EDIT: Don't let it stop you, though, Alex. Another $200-$300 on that bad boy, and it'll look great. Probably still won't work, but dang it'll be shiny. (J/K, man. I'm impressed that you're working on it like you are.)

I now understand the wisdom it takes to be an Audioholic Overlord

 

[Adam]

I now understand the wisdom it takes to be an Audioholic Overlord

Nah, no wisdom here. Just an incessant stream of posts about beer, flip-flops, bad jokes, and quotes from owner's manuals.

 

[highfigh]

Perhaps you're not understanding me here, Using every DMM i have ever used, on the diode function it will display the voltage drop through the diode. Which is why I said it should likely read something such as .6v

I don't remember seeing you refer to the diode function on the meter and since not all have it, I don't think it should have been assumed.

 

[Alex2507]

It makes me wonder what the solder side of the board looks like.

Just when I thought I had plenty of pic's ... The other side looked good.
I replaced those resistors and like Haoleb suggested, unplugged it completely to test the problem
of the fuse blowing and the unit going into stand by. That volume board is not the main problem.

The fuse blows if the transformer is plugged in and even if it's not plugged in the unit goes into stand by mode.
The manual specifically points at the output transistors as potential culprits in this scenario.

I have replacements in hand should I determine that my problem lies there.
That's for later though. I am not going to be up half the night working on this ... again.
Tomorrow is about getting the girl to the airport and going to a cookout so not then either.
Stop pushing me.

Post #29 has the schematic but here it is again:

http://manuals.harman.com/HK/HOM/Service Manual/AVR20II sm.pdf

 

[Haoleb]

With the main power transformer not plugged in, it will not come out of standby mode because there is no power supply. When you plug it in, it should go into standby mode, and when you hit the switch it triggers a relay which turns on the main power supply circuit, You should be able to unplug the connector that just powers the amp section and it would probably turn on completely. Unless there is something programmed in to keep it in standby without feedback from the amplifier board.

 

[Alex2507]

With the main power transformer not plugged in, it will not come out of standby mode because there is no power supply. When you plug it in, it should go into standby mode, and when you hit the switch it triggers a relay which turns on the main power supply circuit, You should be able to unplug the connector that just powers the amp section and it would probably turn on completely. Unless there is something programmed in to keep it in standby without feedback from the amplifier board.

There is a small stand-by transformer. With the main transformer plugged in when I plug the unit into 120 V the light on the power switch turns red. Pressing the power switch turns it green and the fuse blows immediately. After 5 or 10 seconds the light on the power switsh turns red again.

With the main transformer not plugged in the fuse does not blow when the power switch is pressed. The power switch still turns green for about 5 or 10 seconds and then goes back to red. There is a section in the manual regarding the protection circuitry that I don't understand yet.

The manual points toward the output transistors and 4 diodes. All of which I have on hand but must de-solder to test. That comes later.

 

[jamie2112]

Well buddy its sounding like a fleeting chance ...........but by all means continue on your electrical conquest............ I think its cool to have a vision..
just kiddin Alex...you know I like you a little.