Mmats DHC1400.1 - Find the missing pieces

[Dr Zeus]

Take a look at this picture. See anything missing??

I wonder why they are gone, and if they are really required... This amp plays seemingly OK until it drawa about 15 amps, then it clips hard spiking to ~20A. It should have a lot more power!

[Perry Babin]

They are there to clamp transients, if I'm not mistaken. I wouldn't expect the amp to draw excessive current because they're not in the circuit.

If the outputs have been replaced, I'd suspect that they're not compatible.

[Dr Zeus]

You caught the transients. This amp has three different builds of outputs, all IRF3710. Fro mthe looks of it, some were replaced and some were not. Also, I found a few resistors and a coil de-soldered and barely touching the PCB so I soldered them back in. I think before I go and replace the outputs I'll test this amp again with the loose components re-soldered.

Do I need all 4 transients for testing full power? Each is rated for 1500w if that means anything for this amp.

[Dr Zeus]

Will IRF3710Z work? Only because Digikey has them.

IRF3710Z Datasheet: http://www.irf.com/product-info/data...rf3710zpbf.pdf

IRF3710 Datasheet: http://www.irf.com/product-info/data...irf3710pbf.pdf

[Perry Babin]

The Z version is the only version likely to work.

If this is for a paying customer, replace the transient surge suppressors.

[Dr Zeus]

IC. This amp has the non-Z version on it now. I'll add up a stack of the IRF3710Z and already have the transients in my cart.

Thanks!

[Dr Zeus]

Should I order a 4080 driver? I wonder if this amp suffers from this being defective. Whomever worked on this amplifier last, had unsoldered 3 of the resistors just an inch north of the outputs in the above picture.

[Dr Zeus]

I removed all 8 IRF3710 outputs to do some points of measurments with the scope referencing amp general ground. There are four 100 ohm resistors connected to Pins 11, 13, 18, and 20 of HIP4080. With the scope set to AC coupling and 2v/Div @ 5us, Pins 13 and 18 are presenting a +-6v square wave. Pins 11 and 20 are showing something either noisy or 'flat lined' on the scope. Is there anything wrong with this? I believe pins 11 and 20 are driving half the outputs. Is the 4080 driver ok?

I have no outputs in circuit at the moment, and also have yet to install the new transients.

[Dr Zeus]

I went ahead and installed two IRF3710Z and all new transients in the amp. The amp powered on with stability so I went ahead and installed all 8 output transistors. With all 8 installed, I could not get the amp to power on because it drags my 10A power supply down and makes some wierd noises. I re-checked all the outputs which all measure up good.

I did not replace the HIP4080A IC, but I did carefully remove it. This IC has probably been replaced once before after I talked with the owner who previously had tried to have it repaired by someone else. With the IC out of circuit, I tried powering the amp which seemed to come on no problem, but I think that caused another problem.

Now, several of the outputs are measureing up shorted across legs more or less. I think running this amp without the HIP4080 installed caused them to fail.

[Perry Babin]

You cannot operate the amp without the 4080 unless it has pulldown resistors. This amp doesn't.

If the 4080 was ever in the amp with defective FETs, it needs to be replaced.

This amp has 4 banks of outputs. Installing 2 wasn't likely to tell you anything significant.

In some class D amps, the deadtime is determined, in part, by the gate capacitance. Having less than the total number of FETs in the circuit can be misleading.