rodek 224ci protect

[sdoom]

Hi ,

Have a problem fixing a Rodek High Current amp model "224ci" . Actually it has no Rodek label on but it looks like an old-school Rodek amp. I belive that Rodek sold out to ACR at that time and I belive that this is a ZED audio amp, at least i found an article stating that those amps where not sold under the Rodek name anymore. The board is probably also used for a 2150 amplifier .

Problem with the amp. It will power up (2x22V at 12.0V DC power supply voltage),it even plays music but goes in protect after aprox. 8 seconds, regardless if music is played or no signal applied.

There is a LM358 op-amp in the power section. Taking the voltages there I found the second half of the op-amp getting these voltages:



In protect mode:
Pin 5: 5.6V (non inv. in)
Pin 6: 9.9V (inv. in)
Pin 7: 0V (out)


Just after power on:
Pin 5: 5.6V (non inv. in)
Pin 6: 5V getting larger until aprox 8V (inv. in)
Pin 7: 9,6V at start then dropping to 0V after a few seconds


Problem is all lines from the opamp end in different resistor/IC-type networks, (only the temp.sensor is connected seperately) so that makes it hard to find why the voltage on Pin 6 increases.

Has anyone ever worked on a 224ci ?

Already resoldered the complete curcuit board and exchanged the LM358P (it looked like it had heat-spots on the top of the housing).

Thanks
Stephan

[Perry Babin]

Pin 6 is part of the turn-on delay. Pin 6 will increase until it reaches ~90% of the remote voltage. The voltage on pins 5 and 6 determine the turn-on delay. It appears to be working properly.

What is the voltage on pin 1 before and after it goes into protect?

[gisewhcs]

Hi!

I have a working 224Ci here, I can take some measurements so that you can compare the values to yours.

Yours is probably the relabeled "Edition", sold by AudioDesign in Germany after Rodek bankrupted and ACR didn't sell these anymore.
AudioDesign bought the remaining amps from ZED-Audio and relabeled them.
And on my board are some prints that say it's the same PCB as in the 275i.

Silly question, but did you check the cinchground?
It often fails and produces strange problems on these amps.

[sdoom]

Sorry for the late reply.

Well GND lines are fine.

I checked the first part of the op amp, here is what I found:


amp in protect:
Pin

pin 1 10V
pin 2 6V
pin 3 10V

during pwr. up /while running


pin 1 0V
pin 2 6V
pin 3 0V


So it seems the opamp is getting triggered with 10V on pin 3 .

I checked the circuit lines and draw a little pic.




I checked the base voltage on that transistor and that stays constantly at 11.8V , regardless if in protect mode or in normal power mode. I guess now that the newtork #4 puts out the 10V causing the opamp to go high with it´s output. Anything I could check at the network #4 ?


Thanks again,

Stephan

[Perry Babin]

It appears that the amp is going into over-current or DC offset protection. Are you sure that there are no shorted or leaking outputs?

Do you see a pulse of DC on either of the bridging speaker wires as the amp attempts to power up?

[sdoom]

Hi Perry

Thanks for looking. Well, definitely no real short in the output stages but I ´ll check for leaks tonight when I´m back home. I´ll connect a scope to the outputs and let you know if there is DC on the output stages.

@gisewhcs : if your 224Ci was open, could you check the voltages on the network #4 ? I think it would help to see where the difference in output pin 1 is generated.

Thanks again
Stephan

[gisewhcs]

I can check the voltages tonight or tomorrow, nut sure.
And I send you an PM!

[sdoom]

Perry was right (as always ) There is some negative DC voltage on the left channel. Right channel is fine.

The reason for taking some time until the prtection curcuit is activated is that the DC voltage is not high at startup , but increases until the protection curcuit is acivated.



Problem now is all transistors in the left channel appear to be fine as they have the same values as the transistors in the right channel (which is working) , at least the diode-tester in my multimeter delivers the same values. Resistor values are identical , too.

There´s no DC voltage on the input (RCA)

Any idea how I should continue ? Are the MPSA12 transistors on the bottem side sometimes causing trouble ? (I remember those where also used in the older Hifonics - amps).

Thanks again
Stephan

[Perry Babin]

Does this amp have a module labeled NW6?

[sdoom]

Yes those are the upper 2 networks on the pic . (red circle) . The one on the left is the left channel network ANW6.

I assumed that the line in the green circle is the output of that network, there is also a negative DC voltage increase when the amp is powered up.

As I found on the board it is also used for a 275i (some resistors are different then).


Link to pic

Thanks

Stephan