Cadence Zrs 9000D

[mike49504]

I recieved this amp in for repair. The guy that owns the amp said he replaced all of the power supply fets, and outputs.

The problem he said he was having is with the outputs.

There are a total of 16 outputs, 8 per side.

If 12 out of the 16 are in the board amp powers up fine but doesnt produce audio.


If all 16 outputs are in the amp within 5 secs it blows 4 of the outputs up.

So i took all of the outputs out of the amp and also the emitter resistors and the resistors next to the emitter resistors.

I cleaned the board off and started soldering new resistors in the amp.

so now i have new emitter resistors in the amp (39 ohm) and the resistors that are inline with them (100k).

I rebuilt the driver board for the outputs with all new ic's and ect.

I have to go through the preamp section of it yet since it appears to have been messed with.

My question is.

If the amp has new outputs, emitter resistors, the 100K resistors, And a rebuilt output driver board in it.

Is there anything else that could blow thoose outputs up when powerd up?

If so wondering what i need to check?

[Perry Babin]

A shorted inductor may be causing them to fail if the drive circuit is not at fault.

The 39 ohm resistors are gate resistors, not emitter resistors.

For the FETs that are failing, confirm that you read 39 ohms from ALL of the gate pads to the pin of the driver board that drives those resistors. Touch the meter probe to the pad, not to the resistor leg.

There's a muting transistor that fails in this type of amp. It's marked D1302 and is generally very near the audio driver board.

[mike49504]

Thanks Perry,

Ill look for that resistor and check the pads to the pins.

How do i check to see it the inductor is shorted?

[Perry Babin]

It's not easy to check the inductor to determine if it's shorted. If you had an inductor ringer, you could use that but I doubt you have one. If you pull two inductors and either swap them or drive a high frequency signal into them to compare them (a safer option), that may tell you if it's shorted. The problem is that the way they are wound, simply moving the inductor could break the short and it would appear to be OK. This is a problem with these large amps that can make repairing them difficult. It's especially fun when you don't catch the intermittently shorted inductor the first time you repair it and it comes back with all outputs and all power supply FETs blown.

[mike49504]

Perry,

Would it be wise to just switch the inductor? I have a the same inductor here that i know works from a different amp . Just asking before i power his amp up and it blows the outputs along with the ic's

[Perry Babin]

You could try swapping the inductor but many times, the leads are very short and it's very difficult to get them soldered in properly.

[mike49504]

If i go agead and power this amp up with a current limiter and the inductor happens to be shorted am i gonna blow the outputs and driver ic's?

[Perry Babin]

Many times, the secondary capacitance is too great and the outputs too weak to allow the limiter to protect the outputs. It may be possible to insert a 3 amp fuse in series between the drain leg and the drain solder pad but I'm not sure that that will protect the outputs. Did you replace the inductor?

[mike49504]

Didnt replace it yet. Im still repairing a few other things with the amp.

When the outputs blew the first time it burnt a hole through the board and burnt the big trace.

Thats how i got it from the guy.

So i repaired the trace that blew apart.

And i took some expoxy and filled in the hole in the board gotta wait til that dry's so i can drill 2 new holes for the output to sit in the board properly.

So wondering should i just go ahead and swap the inductor ?? I know you said it can be a pain sometimes

[Perry Babin]

Unless the other amp is a junker or you have a source for a new inductor, I wouldn't pull it from the other amp.

If you're going to have to apply heat to the area you epoxy, I wouldn't use mercaptan cured epoxy (most fast cure epoxies). When you apply heat, you'll know why. JB weld is a much better choice.

In the future, I'd suggest referring all of these amps that use the IRFP360s (or larger amps) to dB-r electronics. That's what I do when someone wants one repaired. Chris is much better equipped to handle strange problems and has better sources for OEM parts. These amps are simply too much trouble and can end up costing more than you can make, especially if the owner blows it after you repair it. Most people want to prove that they can repair the large amps but after they get a few that take 3 days or more to repair, they'll reconsider. The smaller amps have a better profit margin unless you specialize in the large amps (like dB-r).