Problem with my Harman Kardon 930 receiver

[sushimaster]

Everytime I turn on/off my vintage Harman Kardon 930 receiver, my woofers on my speakers "pushes out and then gets sucked back in." Almost violently.

I have tried different speakers with the same results.

Does anyone know what likely could be the problem?

- Sushimaster

 

[SoNic_real_one]

Some of the capacitors in the final power stage dried out. You should replace all of them. Start with C603, 604 (623, 624 on the other channel).
Also the ones in the power supply might be of lowered capacity - replace them too.

 

[sushimaster]

Thank you very much. All the capacitors are still original, so that makes perfect sense!

- Sushimaster

 

[latala]

I have 20 or so different models of HK receivers Among them a few 930,s I am sorry to tell you this has always been a problem with this range
I have always switched off the loudspeakers using the spk switches to avoid switch on /off thumps
There are no time delay relays to do this for you The amplifier is always going to thump as it is inherent in the design remember it nearly 40 years old having said that its still a good sounding piece of kit
regards Trev

 

[thetube0a3]

I assume yours is doing what one of the HK 4ch receivers I had did. It would push the woofers all the way out and hold them there for a bit. And then pull them all the way in for a bit, literally seconds for each.

I don't remember the 930 I had doing this. Nor can I accept its normal as there seemed to be A LOT of power there. It wasnt the typical power on thump.

I never fixed the HK I had that did it so I have to assume sonic_real_one is right.

The tone controls also seemed to move the woofers in\out if you spun the knobs back and forth.

 

[latala]

Change all the caps you want it will stilll switch on with a large thump its to do with the vas stage having a resistor and bootstrap There is no way to keep this topology and not then use a relay timer if you want to avoid the thump I used to selll these when they were brand new ! I always instructed my customers to use the spk switches
The amount the spk cone moves is effected by the cabinet loading infinite baffles were not so badly affected as say a bass reflex due to the spring effect of the trapped air
regards Trev

 

[thetube0a3]

Hmm.
latala may be right.

Altho due to age i'd personally still replace all of the alum electrolytics. All should be cheap except for the filter cans. Those you may want to check and just leave if working good.

If this is normal which unfortunately it may very well be, you may want to simply turn the speakers off via the speaker switch before turning the 930 on and off. When you turn the receiver on simply wait 5-6 seconds before turning the speakers on. This is exactly what a timed protection circuit typically does.

I'd also check to see what kind of DC you have on the speaker terminals after the receiver has been on for a few minutes just to be safe.

 

[tiefbassuebertr]

Everytime I turn on/off my vintage Harman Kardon 930 receiver, my woofers on my speakers "pushes out and then gets sucked back in." Almost violently.

I have tried different speakers with the same results.

Does anyone know what likely could be the problem?

- Sushimaster

In temporal section between "OFF" mode and "ON" mode most of power amp topologies haven't perform steps to prevention popping inside the power amp circuit itself. Therefore a lot of circuits exist to drive a relay together with DC and over-current protect for speaker interrupting. A good known integrated circuit (sip outline) was released from Hitachi, Toshiba and NEC
http://www.ic-ts-histo.de/fad/ics/ta7317/ta7317br.htm
But in this model no protect unit with relay is in use. This means, an appropriate modification of the circuit is necessary.
Who know the right steps ?
In the attachment several images of this model after modification by a professional company special made for old (vintage) stuff - images in genuine condition under
https://tonbandforum.de/showthread.php?tid=10082
more images from me:
https://www.diyaudio.com/community/threads/harman-kardon-930-bias-adjust.239812/page-2 (post #23)
https://www.diyaudio.com/community/...-hk-930-popping-noise-troubleshooting.343732/ (post #29)

 

[tiefbassuebertr]

Images from an other device, modified in the similar way
I am looking for a defective device of this model - but only from Germany (cheapest shipping costs) - go to
https://www.ebay-kleinanzeigen.de/s...hk930-in-defektem-zustand/2254323816-172-4899