Help Needed to Troubleshoot

[ngccglp]

Hi,

I think I may have blown one of my 4430. I was playing, suddenly one side there is no sound. I immed turned off the amps. There is strong burnt smell emitting from the port of the 4430. Also I noticed the 2235H is permanently in the 'push' position. I tried to push it back in but its very stiff.

1. Could it be that my amps are faulty resulting in the blown speakers? Which part of the amp is most likely damaged?

2. I know for sure the XO is gone judging from the smell, but is the 2235H salvageable?

Thanks

[jblbgw_man]

Many scenarios but the most common would be the output of your amp going DC through short circuit output devices, causing the output to go to either DC Rail (depending on amp but around 60 Volts DC) this is then applied to the Voice Coil of the 2235H causing that to overheat initially, then causing the Voice Coil to distort on its former thus wedging it in the gap to the point where it then becomes lodged in the gap, then next stage is that either the fuse blows in your amp or the Voice Coil eventually ends up open circuit. The overheating process will generate a “burnt smell” which is probably what you are smelling. It is probably unlikely that the series inductor L102 is damaged, but quite possible that the contacts on the light duty switch S1 and/or S2 could be damaged through the high current. Because of DC blocking series capacitors in the HF section it is probable that the HF section is ok. This assumes that you are using a standard 4430 factory xover and operating it in the passive mode ……….recone the 2235H and you should be ok ……….. But remember get that amp checked out before connecting it to anything else … EVER!! A simple test would be to disconnect the amp from both speakers and use a DC volt meter and measure the DC Volts at the speaker terminals; if the amp has gone DC you will see either rail present at the speaker terminals …. UNLESS the internal protection fuse or breaker is fused/tripped thus removing the supply rail to the output stages……… good luck.

[ngccglp]

Thanks for the tip, I will investigate this weekend.

[jbl]

Sorry to hear this. If the amp did go DC, it should have tripped the output relay to protect the 2235H.
I would check the schematic of the amp to be certain that it has a speaker protection relay. If not, get an amplifier that does.

Ron

[ngccglp]

Hi just an update.

It was confirmed that some of the transistors was blown resulting in DC going directly to speakers. The amp was sent for repair and I just collected it yesterday. These old designs do not have a protective strip, will trade for something else when the opportunity arises. I opened up the amp and noticed that the replacement transistors are of a different color (green) from the original (black), however, the shape is the same.

How could I know if the replacement transistors are the same specs as the original ?

Hooked it up to the damaged speakers. Apparently the 2426 seems ok, so it seems I only need to recone the woofer. I think that would mean that my XO are still OK.

Thanks for the advice.

[jblbgw_man]

I opened up the amp and noticed that the replacement transistors are of a different color (green) from the original (black), however, the shape is the same.

How could I know if the replacement transistors are the same specs as the original ?

Ignore the colour difference, you will find that the older transistors are probably no longer available, or a special numbered device by the manufacturer and not available in the general market place. If the repair was done by a reputable tech he has most likley installed output devices that exceed the original spec due to advances in semiconductor technology...... Good to see you up and running again.

[a_fossen]

had a friend wirh a Mark Levinson amp and the transistors was matched with colour, so if you ordered a new for the posetive it would match the negative transistor (pnp match npn transistor) nb! bias had to be adjust as normal. a_fossen

[subwoof]

Color means nothing because replacements and even newer versions of originals can be a different color. That's just tweako talk..

sub

BTW check the large coil on the crossover ( it is mounted off the circuit board ) to make sure it was not also damaged. If it shorts out the amplifier will see a AC impedance of almost zero due to the LF bypass cap and will blow the amplifier again.

[ngccglp]

Thanks, Checked the coil, looks ok and did not see any signs of burnt/melt.

May I know roughly how much does a full recone kit for 2235H costs?

Thanks

[subwoof]

In the EU the prices can be all over the map so I suggest calling around.

Here in the US it's around 180 + depending on the relationship with the reconer.

sub

[duaneage]

Get this and build it. A lot cheaper than a recone

http://www.audioxpress.com/bksprods/.../kv-k4700u.htm

[ngccglp]

good news, the repair man commented that the VC could be re-used and the paper only bubbled due to the heat generated.

[BMWCCA]

The amp was sent for repair and I just collected it yesterday. These old designs do not have a protective strip, will trade for something else when the opportunity arises.

May we know what the amp is, or did I miss that detail?

Glad to hear you're getting it all back together.

[servojohn]

good news, the repair man commented that the VC could be re-used and the paper only bubbled due to the heat generated.

Why bother? If the reconer is tearing apart the speaker to that point, just have him install the whole kit. It heated up via the voice coil in the first place, and if it got hot enough to melt the glue at a nearby joint...

Have you seen the old voice coil personally?

Best regards,

John

[3dbdown]

IMHO, find another repairman. Never stand on a dollar trying to pick up a dime. You have a high-end speaker there, and as was just pointed out, once the paper burns, the glue deforms, the VC can loosen or shift in spots, and with JBL's gap tolerances, you are asking for trouble in the near future.