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Help! Hum/Hiss in a Harman Kardon 430

MD1032

MD1032

Active Member
Hey all,

I just got a Harman Kardon 430 off ebay to take to college with me since I can't bring my parents' Pioneer SX-3700. So far it seems to work fine, but there is a noticeable hum/hiss when it's turned on, regardless of source, and regardless of channels. It's noticeable to the point where if I turn the amp off, I notice it's quieter in the room. I'm sure a hiss is normal to some extent, but the hum is what has me worried.

I noticed one thing about this amp and that's that I doesn't use a three-prong plug. Would connecting an earth ground somewhere alleviate this problem?

Is there any way of bypassing the bass/treble/balance controls to make sure they're not related?

Also, what is this little needle thing for? It never moves. This unit's a little beat up. I hope everything's all right.

Any suggestions would be greatly appreciated. I haven't cracked it open so I don't know what the inside's like yet.
 
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The "little needle thing" is a tuning strength meter. It should only move in tuner mode, and will (should) swing to indicate the relative strength of the station you are tuning in. If it doesn't move, then it's stuck. Search on AK here and you'll find some threads about HK 330c/430 tuning meters and how to "unstick" them.

The hum/hiss is probably corrosion in the knobs and pots. Another search on DeOxit cleaning will tell you how to cure that. If it's more to it then that, then we'll need to troubleshoot later. A good cleaning comes first.
 
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I noticed one thing about this amp and that's that I doesn't use a three-prong plug. Would connecting an earth ground somewhere alleviate this problem?
Click to expand...
No ..Most likely though a good deoxing of the switches and potentiometers(pots) as Scorpion suggested may clear up your little annoyance.:yes:
 
Unfortunately, the 430 does not have the preamp jumpers that allow you to seperate the amp from the pre-amp section. This would help narrow down the problem, you should have gotten a 730 :].

Anyway, constant hum is sometimes a symptom of bad filter capacitors, those are the two big black cans sitting next to the transformer. I have not personally seen this in any receiver, but it is allegedly a frequent cause of low level hum under all operating conditions.
 
All right, well, deoxit didn't do it. The pots are happier and smoothly sailing now, but the hum and hiss is still there. Are you sure it has nothing to do with these treble and bass controls? Because when I turn up the bass control, the hum increases, and when I turn up the treble control, the hiss increases.

Gah, this is a complete pain in the butt. I want this amp to be completely silent. The amount of noise it produces now is pretty small, but it shouldn't be there at all.

If you think I should contact the seller and return it, let me know. I have that option still.
 
You probably have some dried up capacitors or even bad transistor or two. Best be look'n for a service manual or a tech.
 
Hmmm, well do you think it's anything serious? Like I said, I still have the option to cut my losses and return it, and I'm not opposed to buying another one on ebay if it means that this one's going to be a huge headache to fix.
 
MD1032 said:
All right, well, deoxit didn't do it. The pots are happier and smoothly sailing now, but the hum and hiss is still there. Are you sure it has nothing to do with these treble and bass controls? Because when I turn up the bass control, the hum increases, and when I turn up the treble control, the hiss increases.
Click to expand...

Did you DeOxit the rotary bass and treble control pots also? There should be small holes in the sides where you can see the innards rotate. Spray some DeOxit in there while you rotate the control back and forth to flush out any corrosion debris. The RakShak small cans of DeOxit are expensive, so if you have a Napa near you I'd get a big can of electrical parts cleaner to use on flush-jobs like this calls for, and save the DeOxit for harder cleanings or critical components.

If the hum/hiss persists, then it's time to start troubleshooting. Does it get worse when a certain function is selected, or is it constant across the board?
 
I already shot the treble and bass pots as well. I shot all of them.

It's constant across the board, regardless of source, regardless of any settings using the buttons on front.

The hiss increases when I turn up the treble and vice versa. The hum increases when I turn up the bass and vice versa. The hum and hiss both increase when I increase the volume and vice versa.
 
In your former posts, you reported hum/noise regardless of source, regardless of channels, but affected by the position of the bass and/or treble controls.

This makes me believe the hum problem is related to one of the two power supply regulator boards.

Many components can be bad, but my first suspicion is directed toward the capacitor C4 on the Rectifier A board. If there is too much ripple at this point (bad capacitor C4), the regulators (Q2 and Q1 also) will let pass some ripple (hum) to the following boards. Q2 is the regulator for the Equalizer board and the Tone Pre amp board. The input to this regulator board comes from a secondary winding on the power transformer which is isolated from the main power section. They are not related.

This board is located under the chassis, close to the power switch.
 

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Wow, thanks for the detail! I'll crack it open and take a look when I get home.

edit: By the way, a local audio repair shop wanted $30 for an estimate... which is outrageous considering I paid $50 for it...
 
Well, good news bad news I suppose. Doesn't look like it's C4.

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By the way, I have a relatively basic multimeter, so I can test whatever you'd like if you want. I'm going to leave it uncased and hook up the SX-3700 for now. :)
 
Hi,

First of all get yourself a service-manual:

http://manuals.harman.com/hk/Service Manual/hk430 sm.pdf

Next, get some way of measuring the ripple on these power-supply cap's.
An oscilloscope is ideal for this :thmbsp:
You can't judge about their quality from just looking at them. They're all old enough to be dried up and causing these kinds of hum-problems.

Hiss is something else. Small-signal transistors in pre-amp circuits go bad and cause this. Probably even defective electrolytics (de-coupling and signal cap's) will also cause hiss. I'd go with some freeze-spray gently spraying the transistors and cap's one at the time. If you're lucky the hiss is related to temperature and will change in strength once you hit the defective transistor/cap. Of course the amp. should be turned on during this exercise :thmbsp:

rgds,

/tri-comp
 
Measure the DC and AC voltages at LP501 on the Tone/ pre amp board (this is the regulated power supply point on this board), by reference to ground. You should have +24.5V DC, but 0V AC.

Measure the DC and AC voltages at point LP54 on the Rectifier A board, this is the + side of the 2200uf cap. What do you get?

Tri-Comp is right, you can't judge caps just by looking at them.
 
Go on page 20 of the service manual.

There is 5 connection points, near the edge of the Tone board, close to the Bass control. The power supply input (LP501) is the one closer to the Bass control. There should be no ripple voltage here.

The link from Harman-Kardon was dead some time ago, save this file on your computer.
 
Gotcha. OK, I just got the values right here. Keep in mind that my multimeter might be out of calibration... I do not know how to properly calibrate it.

LP501:
21V DC
40V AC

LP54:
25V DC
50V AC

So indeed, there's alternating current at both places!
 
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