Harman Kardon AVR 20II Repair (pics)

[Adam]

...this useless piece of f^%&ing sh!t.

Hey, that's not a Sony.

 

[Haoleb]

Most of the parts that radiotrash sells are like 5-10% spec parts so dont expect perfection with them. They also sell a kit with 1% metal film resistors I think too. I just order all my parts from mouser.

I think before you get too deep into fixing that volume control board you should try and find out why its not turning on. Cant give you too many pointers but you might want to just disconnect that volume board all together and see if it turns on. If it blows the fuse again check the output transistors for being shorted. There are plenty of how to for checking transistors online, You'll probably have to look up the spec sheet and see if they are NPN or PNP which will determine how you test them

 

[Alex2507]

Haoleb,

All the resistors on that board are 5% tolerance as indicated by the gold band so I'm fine with that. The Radio Shack is a 5 minute walk from me and the resistors are 99 cents for 5 of them so...

Googling 'output transistors' has me looking around at different things. My inner geek is crying tears of joy.
I don't know how to thank you.

Edit: All kidding aside I see that there are a mess of them on the heat sink. I can't wait to figure out how to check them. They don't 'look' fried. This probably wouldn't take so long if I wasn't fooling around.

Check your User CP.

 

[Swerd]

Alex

I pretty much speak up only on things I know something about - building DIY speakers - unless I can sling around enough geeky vocabulary on a subject to fake it.

You may be a chimp, but you already know more about repairing electronic gear than most primates, including me. Just remember that the receiver was put together by someone with at least a little bit of intelligence. So if you have at least that much, you can find the problem and fix it.

If the power never stays on for more than 2 seconds, look at the power supply circuits first. If the main power supply is blown, I'd call it a loss and move on.

 

[highfigh]

Edit: All kidding aside I see that there are a mess of them on the heat sink. I can't wait to figure out how to check them. They don't 'look' fried. This probably wouldn't take so long if I wasn't fooling around.

Those are the output transistors and if you remove them, you'll need to put heat sink compound on them. They don't necessarily look bad, even if they are. Resitors and caps are a different story.

 

[Alex2507]

I got my resistors soldered in and put everything back together only to have the fuse blow. I even had the jumpers out for the pre-amp/amp connection. I could use a game plan. I don't know how to test anything. If you need a specific pic just say the word.

 

[Alex2507]

Current Status

Bandphan sent me a service manual. It says to check the power transformer and some output transistors. I don't know how to do that. I found a page in the manual that tells you if the transistors are NPN or PNP and there is a page that lists the B-C-E of the various transistors. My multi meter has a little hook up for that but it looks like you need an attachment. Basically if I can't conduct tests with a volt-Ohm meter, I'm in too deep (for now). My multi meter runs off an 9 volt battery. I've been pretty careful about not testing diodes with it because I'm not sure if they can take the voltage or amperage used in obtaining a resistance reading. I used it on the output transformers to sniff around and I hope that's okay.

Can the output transistors be tested without removing them?

I found something very odd. The negative on my left rear speaker connection has no continuity with all the other speaker negative connections as they have with each other. It's in a spot where I can't easily get to it nor can I easily track the source for the rear speakers to disconnect them completely. I would hope this is a clue that can be used to diagnose the problem.

 

[Haoleb]

When testing diodes and transistors you use the diode function on the multimeter. A diode should read something around .6v when you test it with the black lead on the side with the band and it should read OL when your leads are reversed. This voltage can be lower if its one of the small glass diodes. Sometimes though you must take components out of circuit to get a good reading. Transistors are kind of the same way, you use the diode test function and put say the black on the C and red on B and E and see what it reads, you'll have to look up exactly what they should read but if no matter what combination of tests you do read something like 0v its a bad transistor.

You dont need to take the transistors out to do a quick check on them to see if they are shorted.

Email me the schematic and I may be able to help you a little more.

 

[Alex2507]

I found this but I think the idea is to have the transistor removed.

http://www.hobbyprojects.com/test_and_measurement/testing_transistors.html

Over at HTS a member has an easy way to come up with the manuals.

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

A Google search says that my 4 transistors are B-C-E with the leads pointing down. I just checked quickly with them still hooked up. I'm too tired to think clearly but it seems to me that these things are only a few bucks so if you have to take them out, why not replace them?

 

[Alex2507]

This is the datasheet for Q216 L/R

http://www.datasheetarchive.com/download/?url=http://www.datasheetarchive.com/pdf/Datasheet-041/DSA00109717.pdf

This is the datasheet for Q217 L/R

http://www.jmnic.com/pdf/2sa/2SA1265N.pdf

This is the datasheet for D208-D211

http://www.datasheetcatalog.org/datasheet/fuji/PX6A07.pdf

It really seems like I have to unsolder these things to check them and I'm hesitant. The situation with the negative speaker connection not having continuity with the rest of the negative speaker connections is a glaring red flag. I just don't know what it means.

My local electronics shop has replacement output transistors for the ones mentioned above for $5 each. My manual says that 4 of them are in question. I don't know. I'm loosing track of my posts here but I still need to figure out how to:

1. Check power transformer for being defective

2. Check primary and secondary for shorts on power transformer

3. Check for short in amplifier circuit

 

[Haoleb]

To truly test a transistor yes you need to take it out of circuit, and hook it to more advanced equipment than a multimeter but for troubleshooting purposes you dont have to remove it. You dont want to just start throwing parts at this thing hoping something fixes it, you want to find the problem.

You can test the transformer for shorts between the primary and secondary winding with your meter set on ohms and simply placing one lead on a wire that goes to the primary winding and the other lead on a wire that goes to the secondary or more windings that are on it. It should read OL. In the schematics it shows a connector that feeds power to the amplifiier section, i would disconnect that and try turning it on which will tell you right away if its in the power supply or amplifier section

 

[lsiberian]

Alex you are truly scaring me. If you do good enough you'll be the first true solder monkey i've ever met.

 

[Alex2507]

In the schematics it shows a connector that feeds power to the amplifiier section, i would disconnect that and try turning it on which will tell you right away if its in the power supply or amplifier section

Pretty swift finding that it had a connector with just the schematic.

I just did that. It goes back into stand by mode but the fuse doesn't blow. I don't follow the reasoning though. Disconnecting the power suppl cuts power to the amp section, right? The amp section, is it just a bunch of those $5 transistors? That negative speaker issue still has me wondering.

 

[Alex2507]

That negative speaker issue still has me wondering.

The rear speakers are connected in series so there is only one true negative connection. So that part is not a clue. I remain clueless.

Back to the drawing board. I'm seriously considering just swapping out my output transistors for ~ $25. I think I'll try to figure out more about the protection circuitry and see if I can get a better understanding of how that works.

Unplugging that connector to the power transformer gave me a chance to establish that there is continuity through the primary (?) and it does not short to ground.

 

[highfigh]

When testing diodes and transistors you use the diode function on the multimeter. A diode should read something around .6v when you test it with the black lead on the side with the band and it should read OL when your leads are reversed. This voltage can be lower if its one of the small glass diodes. Sometimes though you must take components out of circuit to get a good reading. Transistors are kind of the same way, you use the diode test function and put say the black on the C and red on B and E and see what it reads, you'll have to look up exactly what they should read but if no matter what combination of tests you do read something like 0v its a bad transistor.

You dont need to take the transistors out to do a quick check on them to see if they are shorted.

Email me the schematic and I may be able to help you a little more.

You won't read voltage from a diode- the .7V is what it takes to switch it. You can check for continuity between the pins, though and if it conducts from one pin to another in both directions, it's toast. It should only conduct in one direction between any pair of pins.

 

[highfigh]

The rear speakers are connected in series so there is only one true negative connection. So that part is not a clue. I remain clueless.

Back to the drawing board. I'm seriously considering just swapping out my output transistors for ~ $25. I think I'll try to figure out more about the protection circuitry and see if I can get a better understanding of how that works.

Unplugging that connector to the power transformer gave me a chance to establish that there is continuity through the primary (?) and it does not short to ground.

The design of the amp will determine what it needs. If it's a direct coupled amp, the driver transistors can go when something else goes out because it can conduct DC voltage, unlike a capacitor coupled amp. Also, the bias resistors can go away- look at any larger resistors that may be white or beige ceramic, for dark spots on the resistir or on the circuit board next to them. The dark spots indicate extreme temperature.

 

[Haoleb]

You won't read voltage from a diode- the .7V is what it takes to switch it. You can check for continuity between the pins, though and if it conducts from one pin to another in both directions, it's toast. It should only conduct in one direction between any pair of pins.

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.

 

[Haoleb]

Pretty swift finding that it had a connector with just the schematic.

I just did that. It goes back into stand by mode but the fuse doesn't blow. I don't follow the reasoning though. Disconnecting the power suppl cuts power to the amp section, right? The amp section, is it just a bunch of those $5 transistors? That negative speaker issue still has me wondering.

i Guess i should have asked which fuse exactly is blowing, as in some designs there are an array of fuses for each section of the amplfiier. The amp section is alot more than just the transistors, it also includes all the circuitry that drives those transistors among other things. Investing in replacing the output transistors wouldnt be a wise move at this point because we havent even established that they are bad.

 

[Alex2507]

If it's a direct coupled amp ...

As soon as I figure out what that means I will get back to you ...

i Guess i should have asked which fuse exactly is blowing ...

It's the main 5 amp fuse that has blown. I'm finding out that proceeding to blow these one after the other is bad ju-ju. I'll pull the output transistors eventually to check them.

I got distracted and started playing around with a different receiver.

 

[Adam]

As soon as I figure out what that means I will get back to you ...

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

"An amplifier in which the output of one stage is coupled to the input of the next without the use of a capacitor. This type of amplifier will amplify Direct Currents and low frequency waveforms."

"A direct-current amplifier in which a resistor or a direct connection provides the coupling between stages, so small changes in direct currents can be amplified."

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.