Hertz HP1D - Output FETs getting shorted always

[coed1992]

hi, i 've been working on this amplifier, it does'nt have audio output, Then suddenly it went on Protect mode while troubleshooting, i removed all the output MOsfets , 4 in each sides. I found out that 1 of them was shorted. for safety I fixed first 4 mosfet 1 in each hi and lo side, then again 2 of the mosfets i the same side Hi and Lo went shorted in no time which made the Supply Fets on the same side go hot. What is causing the output Mosfets to get shorted? I don't want to replace another one because it might short again. Please i need help who came across this problem. Thank you very much.

 

[Perry Babin]

Did you replace the driver IC for the FETs that failed?

 

[coed1992]

No not yet, you mean if its driver IC's fail then it will short the FEts as well ? let me pull out the driver board and and replace the driver IC. Thanks again bro, will get back to you , the status of the repair.

 

[Perry Babin]

Virtually every time that the outputs fail, the driver IC fails. In some cases, where there are buffer transistors, the ICs survive but you can plan on replacing the IC every time the output fail.

In many cases, the failure of one IC leads to the failure of all driver ICs.

 

[coed1992]

thanks for the info bro, it is a big help for us still beginners to car audio repairs. I will get back to you any progress of the repair.

 

[coed1992]

I pulled out the driver board DWM3640AD and I believe the iC's U1,U2,U3, and U4 are
U1(IRS21844S), U2 (TL072) , U3 (LM211) and U4(IRS21844S) respectively? Thanks.

 

[Perry Babin]

I'm not 100% sure on this board but that sounds right. For the LM211, confirm that pins 1 and 4 are directly connected.

 

[coed1992]

Good day bro, yes as I pulled out the DWM360 driver board and about to changed the two IRS2844s because I measured a short at pin 13 and 11 of this chips which is causing the out Fets on low side to blow but what I noticed of the CL1 and CL4 circled red in the picture have different value 30k ohm and 5 Mega ohm respectively. I'm not sure of these components but are these capacitors ?, what are the correct value of these components as they are directly connected bet. 13 and 11 of the driver chip. Thank you mate in advance.

 

[Perry Babin]

They are capacitors. The value varies, depending on the amp but they're generally between 4.7 and 6.8uF.

 

[coed1992]

Thanks mate, so i can order any value between 4.7 and 6.8uf ? but can i use a 50v multilayer ceramic capacitor, what size shall I order?

 

[Perry Babin]

The cap will never see more than the IC can withstand so 50v is OK. That said, I generally used the highest voltage that would fit the pads.

 

[MikePP]

Take them off the board and measure again to confirm they're damaged/leaky.


And take care not to over stress them removing them (with heat) to avoid damaging what could be a perfectly good cap

 

[coed1992]

Is there any issue if will just fixed the new IRS21844s without changing these capacitors? Because it is really pain looking for SMD parts here in Dubai, not much dealer here, i have to order in Aliexpress and it takes 3 weeks to arrive here.

 

[Perry Babin]

Please don't post in a repair thread that was started by someone else unless you are trying to help them.

The caps sometimes fail and sometimes survive. Refer to post #12.

Start a new thread if you have other questions.

 

[coed1992]

Thanks mate. I Believed one of the caps did not survived, so I will just order them as well. These are ceramic capacitors? . Am i right?

 

[Perry Babin]

Yes.