Rodek 275i (ZED Audio) amp

[Dr Zeus]

Between the left most two, I measure 8.2k.

From left to right

Pins-to-pin
1-3: 22k Ohms
1-4: 22k Ohms
1-5: 22k Ohms
1-The rest: OPEN

2-3: 13.8k Ohms
2-4: 14.6k Ohms
2-5: 13.8k Ohms
2-The rest: OPEN

 

[Perry Babin]

It's leaking internally. I'd suggest that you cut the legs for the first two pins and the last two pins (or at least bend them so they can't touch the board). Then install two 8.2k resistors (on the bottom if you can't make the leads clear the leads on the module).

 

[Dr Zeus]

Is that a permanent fix? Who the heck made these modules! LOL

 

[Perry Babin]

If ZED can't supply a replacement module, it's a permanent repair. You can also replace the entire module with discrete parts but that's up to you.

 

[Dr Zeus]

Good progress. Installing 8.2k resistors fixed the left channel.

The right channel's module tested out OK on the bench. I'll play more with this tomorrow.

 

[Perry Babin]

Some only leak when higher voltage (higher than the ohm meter can apply) is applied.

 

[Dr Zeus]

Looks like both channels are fixed with jumping 8.2k resistors across the 2+2 end pins of both ANW7s.

Should I put Q1 back in? I removed it to get the amp out of protecting modes.

 

[Perry Babin]

Yes. It was only removed to allow you to determine what type of fault was tripping the protection circuit.

 

[Dr Zeus]

Whoops. Spoke too soon. Put Q1 back in and the amp is coming on in protect mode. I pulled it back off again and the amp powers up and plays fine both in channels.

Whats the harm in leaving Q1 off the PCB?

 

[Perry Babin]

It defeats the protection circuit. If an output shorts, it will do much more damage if the protection circuit can't shut down the amp.

Did it have any DC offset after you replaced the resistors?

 

[Dr Zeus]

Before the resistor mod, the amp was measuring ~30vDC on both channel outputs. Now, the amp is measuring 0.025vDC across speaker terminals. Referencing amp's general ground each speaker terminal has ~0.3vDC.

 

[Perry Babin]

Reinstall Q1 and remove Q3 and Q4.

 

[Dr Zeus]

/Reinstall Q1 and remove Q3 and Q4.

Amp still comes on in protection mode with Q1 in and Q3/Q4 out.

 

[Perry Babin]

I sent you a diagram. Confirm that transistors Q3 and Q4 are connected as shown in the diagram.

 

[Dr Zeus]

Following the diagram is wrong for my amp, unless in the diagram I swap Q2 and Q4. On my amp, Q4 is the MPSA12, and Q2/Q3 are 2389s.

I confirmed my Q4 is connected to C7 and also NW6.

My Q2/Q3 are hooking into the NW5

 

[Perry Babin]

If 2/3 are connected as 3/4 in the diagram, remove them and reinstall the other transistors.

 

[Dr Zeus]

Only Q2/Q3 are off the board now. The amp still goes into protection mode.

 

[Perry Babin]

Find an NPN transistor near the outputs that has its emitter connected directly to the bridging speaker terminal for that channel. It's collector will go to one of the terminals on a module marked NW1. The circuit board designation is likely to be the highest number in the channel (ignoring the outputs).

 

[Dr Zeus]

I believe they are 15028 (http://www.onsemi.com/pub_link/Collateral/MJE15028-D.PDF) on the power supply fet side of the board as Q109 and Q209. The center pins of these are connected to the center pins of all the output transistors, and also to the bridging channels but first through what i think is a 1N4004 diode.

These dont seem to come close to the NW1; which looks more like to-do with the gain control and possitioned near the RCAs. NW1 is a 8 pin Zed circuit.

 

[Perry Babin]

This would be a small transistor. Possibly a 2sc3289.