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Help--Need a Harman Kardon 430 tech.


JohnW
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I'll go out on a limb here... are the lamps in the 430 in sockets, i.e., like fuse holders? I blew up a receiver once... put a fuse in a lamp holder. It took out to much for me to continue when the power came on.

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3 minutes ago, JohnW said:

Yes, but it was only a .3v diode drop on both pins—reading went from 1.0 to .692

 

Are you reading .3v with the meter or .692v? I can't tell if you are subtracting .692 from 1 and coming up with the .3v, that's not how it works. If when you connect red probe to base (pin#3) and black probe to either emitter or collector and your meter settles down to reading .692 then that looks like a good reading and I would say it's fine. I typically remove and test out of circuit.

 

If this was my amplifier or needed to repair it I would take that board out and remove D6, D7, and Q1 and test out of circuit. Then I would remove C1, C3 and C4 and test those but more likely since they are out just replace them due to age.

 

+B3 powers the AM/FM circuitry so look at that also and make sure there are no shorts there. Once everything is checked or replaced on the regulator board then carefully power it up with a voltmeter across R9. Since we know they are using a 1/2 watt resistor I would expect current draw to be quite low, maybe 100mA-200mA. So during normal operation you might see around 1v drop across R9. If when you first power it on and you see the voltage across R9 creep up to 2v or more shut it down there is a problem. A 2v drop across R9 is 487mA and you know the 1/2 amp fuse is going to blow soon.

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Instead of continuing to blow resistors keep a volt meter connected across R9 to monitor how much current is being pulled through it, as I mentioned above anything more than 2v across it there is a problem.

 

If everything on the regulator board is fine the problem must be on the load side where +B3 feeds. Looking at the schematic it looks like it powers the AM/FM circuits so check that section also. You must have a dead short somewhere like a bad transistor, diode, or capacitor.

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1 hour ago, JohnW said:

Ok, multimeter across R9 set for 2 volts reads fluctuations from -.02v to +.02v

 

should it be fluctuating, or hold steady?

 

That's what you read with the amp on? Is the fuse blown?

 

What you want to do is read the voltage across R9, that's one test lead of your meter on each lead of R9. Turn the amp on and watch the voltage, if it passes past 2v shut the amp off.

 

It's a way to see if the circuit is pulling too much current before doing any more damage like burning R9 up or blowing the fuse etc.....

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1 hour ago, JohnW said:

The fuse did not blow. I measured it without the resistor in the circuit. You’re saying I should put the resistor in before I measure?

 

oh ok lol yes that explains it, sorry I should be more specific in troubleshooting tips for people and not assume they do this stuff all the time.

 

You can't measure a resistor out of circuit and read a voltage, that would be wild. Out of circuit just check the resistance value to make sure it's what it should be, in this case 8.2 ohms.

 

The troubleshooting tip I was trying to explain was for when you get done troubleshooting the regulator board and it's all fixed or working properly and you install it back into the amplifier. When you then go to power the amplifier back on is when you want to do what I am suggesting. We use ohms law all the time to figure problems out.

 

I = V / R

 

I = current

V = voltage

R =  resistance

 

No voltage across a resistor out of circuit because there is not current. By looking at the wattage rating of R9 and the current rating of the fuse I can extrapolate roughly how much current that should be in that circuit. To measure the current easily we use ohms law and instead read the voltage across R9 which since we know the resistance value of R9 we have two variables and can solve the equation to find the third. When you power the amplifier on while watching your meter reading voltage across R9 and you see it rise to 2 or more shut the amp off to protect it from doing any more damage and burning R9 up again. Plugging 2v into the equation we get.

 

2 / 8.2 = .243

 

Why do I think this is amount of current shows there is a problem? Like I said the wattage rating of R9 being a 1/2 watt resistor. Let's figure out power through the resistor.

 

P = I * V

 

P = power in watts

I = current

V = voltage

 

.243 * 2 = .487

 

so .487 watts

 

The 1/2 watt (.5) resistor will get very hot running like this but it's within it's ratings. Most likely the circuit is pulling less than this amount but we can easily say that there shouldn't be more than 243mA flowing in that regulator circuit just through reasoning, deduction, and a little math.

 

 

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Here’s a new discovery…

 

every diode, resistor, capacitor on Rectifier A board shows at least some conductance…

Except this little guy, which is the next link in line after the R9 resistor. 
 

Ok forgive my ignorance, but what is this? The C5 capacitor (which seems to be conveniently missing from the HK parts list)?

 

 

8A88CDDF-9298-433B-B2F5-FCFF6F699EB0.jpeg

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On 2/12/2022 at 4:23 PM, Marvel said:

I'll go out on a limb here... are the lamps in the 430 in sockets, i.e., like fuse holders? I blew up a receiver once... put a fuse in a lamp holder. It took out to much for me to continue when the power came on.

Thankfully, no. These are for sure fuse holders. Labeled as such, and on the bottom of the unit. 

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And while the capacitor seems to be missing from the Rectifier Board A list, the list does include two zener diodes, which I can't seem to find anywhere on the board. 

But I'm highly inexperienced, so maybe I just don't know what they look like. 

 

zener.JPG

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48 minutes ago, JohnW said:

Here’s a new discovery…

 

every diode, resistor, capacitor on Rectifier A board shows at least some conductance…

Except this little guy, which is the next link in line after the R9 resistor. 
 

Ok forgive my ignorance, but what is this? The C5 capacitor (which seems to be conveniently missing from the HK parts list)?

 

 

8A88CDDF-9298-433B-B2F5-FCFF6F699EB0.jpeg

No, it's in the parts list. And I just pulled it out. It's fine. Tested perfectly at 47uF.

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