Harman Kardon 330B blowing outputs

jcon109

Active Member
I have a HK 330b that I loaned out to someone. When it was returned the person told me it quit working.

After some testing I discovered the 4 output transistor were bad. (2sc1107). I also tested the driver and predriver transistors and they tested good. A conducted a good visual inspection and nothing else looked burnt or damaged. Replaced the outputs with 4 TIP41c and fired it up with a dim bulb tester. Everything worked and sounded great with 15 watt, 40 watt, 60 watt then 100 watt bulbs. I thought I was safe. I then tried it plugged into the wall and it blew all 4 output transistors (actually blew two of them into pieces, one on each channel)

Any thoughts on where to look?

Thanks.
 
You may want to to check the bias diode to see if it open or shorted. Also check the boas pot to see if it is open.
Where did you get the TIP41C?? if on ebay they could be counterfit, but I have gotten some from there and never had a problem like you experienced.
Lastly double check all the transistors again and make sure that none opened, shorted or are leaky. You may need to remove them to check for leaky.
 
I did get them off ebay... I have some tip31 from Mouser I think will sub as well. Just seems odd they would explode like that. I am still a nube on testing transistors. I did remove all the transistor and check from a post from Echowars . Not sure how to check for leaks? I will check the bias pots as well tonight.

Thanks
 
I wouldnt get anything off ebay. If its a rarer part you need and the main stockists dont have it - try BDent.
 
I prefer MJE15030G or MJE15032G for the output transistors at Q411-Q414, but always replace resistors R431-R434 and trimpots VR401-VR404.
 
Hi jcon - did you solve this issue? I have a similar situation with a 330b.
Thanks

Simplest approach:

Make sure your speaker protection fuses are 2A fast blow. Factory calls for 1.5A, but 2A is fine.
Replace all the electrolytic caps, at least those in the power supplies, the preamp "control" board, and the main amp board.
Measure the resistance of the emitter resistors at R431 through R434.
Replace the four trimpots on the main amp board.
If that doesn't work, sit back and have a beer.
 
I'd start by lifting the leg of the emitter resistors, the high wattage resistors surrounding the output transistors. These get stressed and often go open (no workie) or short (bye bye output transisor).

The bias, DC offset, and DC balance trimpots should be tested (and likely replaced). You've already done this, so you might want to just test to see if the value is right

One next approach is to use the transistor voltage chart and find any transistors who are getting or delivering a significantly-different-than-chart voltage. That should help narrow the "where is my problem" part of the troubleshooting. The transistor might not be bad, but the components nearby should be tested.

If you've replaced all the electrolytic caps and you're still having problems, then re-check the polarity of the caps you installed. I've gotten the positive and negative mixed up more than once.

If you're still having problems or wrong voltages, then it's time to check any diodes (in this case the varistors).

If they all check out good, then it's time to check the value of ALL the resistors. They can drift or short or go open without visible evidence. Lift one leg, check on a DMM, and compare to the schematic.

After all that, if you still are having problems, the only thing left are the film and ceramic caps. Not usually a problem, but easy to test. Again, you don't have to lift one leg and use a component tester ($20 on eBay or Amazon) to find the cap's current capacitance.

At this point, you've tested all the components.
 
An alternate approach, the one I mostly use because I'm not trained, is to shotgun replace everything on the board. On every order from Mouser, one shipping charge, lots of desoldering and then lots of soldering. For me, this is the lower cost, less time, more confident-it'll-work-and-last approach.
 
Back
Top Bottom