Cadence CPA245

Frycztech · 2017-05-19 4:54 pm

Someone gave me this amp a while ago and Iam trying to learn more and fix it so it was missing a fuse and I put a fuse back into it and tried to power it off my power supply and the light on the supply shuts off when its connected. So I believe that there is a short. Any help would be appreciated!

Perry Babin · 2017-05-19 5:23 pm

If the excessive current draw is only after remote voltage is applied, the output transistors are the most likely culprit.

Frycztech · 2017-05-19 5:59 pm

I just checked it happens as soon as I connect the battery terminal

Perry Babin · 2017-05-19 6:01 pm

That would likely be either shorted power supply FETs or a shorted reverse protection diode. If the FETs don't read near 0 ohms from leg 1-2, it's likely the reverse protection diode.

Frycztech · 2017-05-19 6:08 pm

So the oiwer supply FETs would be the 2 IRFZ44 at the top right? And leds 1 and 2 would be the gate and drain?

Perry Babin · 2017-05-19 7:54 pm

yes and yes

Frycztech · 2017-05-19 7:58 pm

The top FET has 7.5ohms the other has 191ohms

Perry Babin · 2017-05-19 8:09 pm

Pull them and check them out of the circuit. They're likely defective.

Frycztech · 2017-05-19 8:43 pm

One has 8ohms between 1 and 2 and the other is showing it is open.

Perry Babin · 2017-05-19 8:50 pm

The open one may be OK but you should replace both. After cleaning the pads so there is no solder bridge, does it draw excessive current when powered up?

Frycztech · 2017-05-20 12:37 am

Yes it dose not trip the supply and is drawing 0.112 of a amp. Where is a good place to order those FETs?

Frycztech · 2017-05-20 3:43 pm

When i search i only see IRFZ44n not IRFZ44. Will thouse work?

Frycztech · 2017-05-20 3:47 pm

Also found a IRFZ44E-ND threw digikey. Would that be a good replacement?

Frycztech · 2017-05-22 12:57 pm

Would any of these work for replacements?

Perry Babin · 2017-05-22 6:53 pm

The version of the Z44 isn't critical as long as it's the same case style.

Confirm that the drive signal is OK before replacing the FETs.

Frycztech · 2017-05-22 6:57 pm

What do you mean by drive signal?

Perry Babin · 2017-05-22 7:00 pm

The signal that drives the gates of the power supply FETs.

Please read the basic repair page (first link in sig line below) in its entirety.

Frycztech · 2017-05-22 7:22 pm

Ok iam getting 4.710 coming into both gate pins.

Perry Babin · 2017-05-22 7:24 pm

That's probably OK. Confirm that the gate resistors for both FETs are within tolerance.

Frycztech · 2017-05-22 7:34 pm

The 2 resistors that are in series for both gates measure good.

Cadence CPA245

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