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Harman Kardon 630 ?

jimcheri

jimcheri

New Member
I have a Harmon Kardon 630 receiver. I want to try troubleshooting.
The 630 comes on and everything is fine until I engage the speakers
The dim bulb tester lights up and all the receivers lights go out.
The main caps are swollen so I am wondering if I just replace them will it come back to life.
How can I narrow this down?
I plan to recap it but I also have 2, 430’s and have been trying to make a list and order everything at the same time.
I have never done a recap so I am a little hesitant.
 
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jimcheri said:
The 630 comes on and everything is fine until I engage the speakers
The dim bulb tester lights up and all the receivers lights go out.
Click to expand...
Might have a shorted output transistor.. Check and see if you have a burnt speaker fuse(s) on the rear panel. Check them with a multimeter.
 
With the speakers disconnected, does the bulb still go bright when the speaker switch is pressed?
If it stays dim check for a DC voltage at the speaker terminals. Should be almost zero.
If there is a DC voltage one or more outputs may be shorted.
If there is no DC voltage check the resistance of your speakers and wires.
With the speaker switch off you can still check operation through the headphone jack.
Your amp looks just like my 430 except more power.
 
Oh wow, yep, those are some bulging caps! Keep your face away from them and handle them with care.

That 630 is beautifully made--I had one and loved the looks and that massive, solid aluminum tuning knob.

If you can solder, I think you can handle a recap. We can talk you through it. I wouldn't worry about ordering all of the caps for all of your receivers at once; take it one unit at a time and work in stages, then check your work with the dim bulb tester and then music listening as the DBT is a very crude test for short circuits. For example, just do the power supply, then check you work.

Sometimes a fuse will blow and you can't see it; did you check them for continuity? Not questioning you; just making sure the super simple stuff is covered before you go chasing more exotic problems. That is odd that the 630 passes the DBT until the speaker switch is engaged--this will sound ridiculous but do you have speakers attached and if so, is there a stray copper strand shorting the terminals at the receiver or at the speaker terminals?

Very nice HK receiver from their Twin Power era and worth the effort, even if you have to take it to a shop.
 
birchoak said:
Oh wow, yep, those are some bulging caps!
Click to expand...
Probably just warped plastic top covers. Push down on it. The aluminum is likely flat as it should be beneath that dust cap. Caps of this type vent out the bottom. Very very seldom do they swell up on top.
 
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avionic said:
Probably just warped plastic top covers. Push down on it. The aluminum is likely flat as it should be beneath that dust cap. Caps of this type vent out the bottom. Very very seldom do they swell up on top.
Click to expand...
I did not know that. Consider me schooled. But I think we can agree that's a nice receiver worth fixing.
 
I have a habit of pulling fuses out to check them, they all checked good and are the right amperage.
The headphones do work
With speakers disconnected the dim bulb stays dim but I have 130mv DC on the left and 30mv DC on the right. That varies with the volume.
It swings to -400mv when I disengage the speaker switch then bleeds down. Should I be using an analog meter?
Looking at the under side of the caps I dont see any leakage. It does feel like it is just the plastic bulging.
The service manual called out some output transistors on the driver board and the three legged critters I think.
I thought they would be the metal one behind the cover. How do I isolate and check them?
Is it easy to buy replacements?
Thank you all for your help.
 

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jimcheri said:
130mv DC on the left and 30mv DC on the right
Click to expand...
Where are you measuring these voltages ? If you have the speakers disconnected from the amplifiers ie.speaker switches ... You can't measure any meaningful voltages at the speakers binding posts.
 
jimcheri said:
I thought they would be the metal one behind the cover.
Click to expand...
They probably are.. Post a photo of them. There should be 4 of them Q901,902,903 and 904.

They should look like these..

sim


Remove the two screws and just pull on them to unplug them from there sockets.They should also have a mica insulator between the transistors and the heatsink. Don´t break the insulator.
 
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Sorry .. this guy is boring as hell.. But you should get the basic idea.


 
Avionic, the patron saint of DIYers! The good news is that those TO-3 output transistors are easy to remove (no soldering) and can be replaced with modern ones if needed. Remember to put the clear mica insulator back on, or buy some Berquist Sil-Pads (negates need for mica, heat sink grease).
 
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I measured with the leads on the speaker terminals
Then pressed the main speaker switch.
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I will pull these tomorrow and check them
 

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I tested all of them and had .525vdc average pin to base and pin to pin the other direction shows .OL
When I touch the leads together.0000 vdc
It looks like those 4 are good.
I put everything back did another visual inspection
Connected one speaker it worked connected both and it still working.
IDK what happened
Transistor leg touching the case maybe??

All the functions work except FM is very very faint at full volume
 
I apologize, I would swear I checked the speaker wire connections at the terminals and removed and reconnected them before all of this.
I must have shorted them with the wires.
I was making assumptions based on the plug being cut off of the power cord and the bulging plastic at the caps.
I appreciate everyones help!
I did learn a lot
 
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