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

[IMGDEAD]https://i886.photobucket.com/albums/ac65/unclemeat2010/amps/IMAG0098.jpg[/IMGDEAD]

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.