Kicker ZX1000.1 repair

[Perry Babin]

All 3 at the bottom are different. They were produced during the same week but are not from the same batch. From the codes on the transistors, it appears that they were produced in weeks 30 and 32 of 2002.

If you purchased them from a local supply house, go back and get 4 more that match.

You use a lot of parts. You should order these in full sticks (50 pcs) so you'll have plenty with matching date codes. Some suppliers will ship only those with matching date codes if you tell them you need matching codes when you order the parts. At higher quantities, they are generally less expensive (less than $1US).

[djQUAN]

I didn't have enough money when I went there so I just bought what I needed.

I was planning on ordering a bunch from ebay but never had enough cash to do so....

if I do scrape up some cash, is this ebay seller good?
fets

[djQUAN]

went back to the local store and unfortunately they only had two left.

the good thing though is that they match the five others in the previous order so I have seven similar fets and three different ones.

I'm gonna take my chances on this one and hopefully pick the best one of the three....

[djQUAN]

ok, so I powered it up for about 3-5min and the PS fets get a little warm without any heatsinking. well, not really that warm. just perceptibly warm. but everything else seems fine.

I went ahead and installed it in the heatsink for further testing as the voltage regulators are getting hot without any cooling and powered it up and played music.

everything runs as normal. output before the output filter is a nice square wave but the first output inductor is getting quite hot and the smell of varnish is coming out of it. it was hot to touch and I couldn't keep my finger on it for a second.

also, the first capacitor (10uF 200V NP) connecting the inductor output to ground is also getting warm.

looks like the inductor core material is toast and I need to replace it?

[Perry Babin]

I'd agree that it is likely defective.

What's the square wave voltage (peak or peak-peak) on the input and on the output of the inductor?

[djQUAN]

square wave peak is similar to rail voltage = 80V more or less... nice square without any spikes or ringing. although there is a little slope on the tops. the sides (turn on and off slopes) are perfectly vertical but the tops are slightly sloping and gradually increasing before the fets turn off. did you get what I mean?

after the inductor, it is a sine wave at about 2Vpk-pk

PWM is 76.9kHz at idle.

edit: gate drive is about 10-11Vpk at 13.8V input. I think it is a tad lower than I would like. is that normal with amps using TL594 and totem pole drivers?

also, four IRF3205's a side should have a lot of current carrying capacity so they should stay completely cool even without heatsinking with 3A continuous draw so I would think something must be wrong at the PS section

[Perry Babin]

Looking at the signal on the gate leg of the PS FETs, you'll probably see a tiny pulse on the falling edge of the waveform. If the pulse occurs before the FETs switch off (~3.3v), the FETs will run hot. The pulse occurs when the other bank of FETs turns on. If both banks of FETs are on at the same time, they will run hot. Does the gate voltage drop below 3v before the pulse.


In this photo, you can see the pulse occurs at ~4v on the bottom waveform (gate leg of FET). This was causing the FETs to run hot.
http://bcae1.com/temp/psP1010089b.jpg

In this photo, you can see the pulse occurs a bit lower than 3v. This was taken after the drivers were replaced.
http://bcae1.com/temp/psP1010091b.jpg


Less than 1v of ripple shouldn't make the capacitor heat up. It may be defective also.

Is there any DC on the output?

[djQUAN]

I remember seeing those spikes at the gates while testing. will check those later.

[djQUAN]

I removed the driver transistors and tested them with diode check on the DMM and all of them checked OK.

it might be due to the fact that I'm using an earlier version of '3205's that have higher gate charges? the gate resistors are rather high at 100ohms.

I could either replace the gate resistors with lower values (which I'm not sure as I don't have lower resistance SMD resistors here and they aren't available anywhere) or I could increase deadtime?

[Perry Babin]

Are you sure that the OEM parts were IRF3205s?

In the Kicker amps that I'v seen with 3205s, they used 47 ohm resistors.

If the resistors are the problem, increasing the deadtime would decrease idle current.