Rodek 275i (ZED Audio) amp

[Dr Zeus]

This amp looks like its going to be fun to work with!

 

[Dr Zeus]

This amp turns on in protect mode. It looks like a real repair company took a stab at replacing all sorts of things; the TL594CN, LM358P, and several small transistors. Taking what I learned from the Hifonics Thor, I'll start tracing back through the parts and hopefully find something other than the proprietary circuits as failed.

 

[Dr Zeus]

TL594:

Pin1: 0.266
2: 4.90
3: 4.88
4: 0.031
5: 1.495
6: 3.539
7: 0
8: 11.92
9: 0
10: 0
11: 11.91
12: 11
13: 4.98
14: 4.98
15: 4.98
16: 8.51

 

[Dr Zeus]

LM358:

Pin1: 9.32
2: 5.5
3: 10.95
4: 0
5: 5.49
6: 9.61
7: 0.009
8: 11

 

[Perry Babin]

There's no problems with either of those components (from the voltages given) but pin 1 is driving pin 16 high. This is likely due to over-current (shorted output) or DC offset.

 

[Dr Zeus]

Outputs check out fine. How would I see if there is DC offset if the amp will not power up?

 

[Perry Babin]

Remove Q1. This will disable part of the protection circuit so you will need to have all transistors clamped and have a 10 amp fuse or a current limiter in the B+ line.

 

[Dr Zeus]

Removed Q1 and the amp powered up and stays on with a 5A fuse. The speaker terminals have 30vDC across them.

 

[Perry Babin]

Both channels (measured directly across the speaker terminals)?

 

[Dr Zeus]

Yes. Measuring 30vDC directly across speaker terminals.

From amp ground to non-bridging terminals I measure 1vDC, and from amp ground to bridging speaker terminals I measure -29vDC

 

[Perry Babin]

Do you have both positive and negative regulated voltage on the op-amp near the RCAs?

Do you have positive rail voltage on the outputs?

 

[Dr Zeus]

The KF347 opamp near the RCAs has +13.4vDC on pin 4, and -16.25vDC on Pin 12.

THe outputs are measuring a tad bit funny. For isntance, Q217 (Posted picture, large output on the right in the middle of the heatsync) is easy to measure:

Q217
Leg1: -29.85vDC
Leg2: -30.67vDC
Leg3: -29.32vDC
-All negative

Q114 is on the other side, in the bottom left corner closest to the LEDs:
Leg1: -29.8vDC
Leg2: +33vDC (Positive)
Leg3: -29.13vDC

 

[Dr Zeus]

The right side transistors are green like the incredible hulk. The left ones are a much more enginerical silicon black.

 

[Perry Babin]

Is there any significant DC on the op-amp output pins?

If there is a Q101 and Q201 (2N5458 likely), post the DC voltage on all 3 legs of at least one of them. Place the black probe on one of the non-bridging speaker terminals.

 

[Dr Zeus]

All input and outputs pins of the KF347 opAmp are measureing exactly +1.080vDC

Q101 and Q201 diode check ok. It looks like a previous adventurer replaced these transistors.

Q101:
Leg1: 0.000v
Leg2: -22.52v
Leg3: -21.87v

Q201:
Leg1: 0.000v
Leg2: -13.60v
Leg3: -21.97v

 

[Perry Babin]

Are all of these with the black probe on one of the non-bridging speaker terminals?

What's the resistance between the RCA shield and the non-bridging speaker terminals?

 

[Dr Zeus]

I had measured the KF347 inputs and outputs referencing amp ground. Referencing non-bridging terminals all inputs and outputs measure 0.000vDC.

The Q101 and Q201 was referencing non-bridging terminals. Invertently, when referencing amp ground Q101 and Q201 measure just +1vDC higher than before.

Unpowered, from non-bridging speaker terminals to rca shield measures 0.4 ohms.

 

[Perry Babin]

Remove the ANW7 module from one channel. Measure the resistance from the two end pins to all of the other pins. They should all read as open.

 

[Dr Zeus]

I'm so proud of myself for desoldering this module so cleanly. Check it out

An externally hosted image should be here but it was not working when we last tested it.

If the 2 end pins are the ones all the way to the right; I only get a resistance reading of 8.2k between just those two pins. Referencing either of those pins, all other pins read as open.

Should I take the other module out for testing?

 

[Perry Babin]

Check the 2 on the other end also.