phase linear D 500 right channel LED not working correctly

[vmaxman]

When powering on my amp, both gains turned fully CCW the right channel LED is initially at the far left. Once the relay engages the right channel LED light jumps to approx 60% of the scale and stays there. When I turn the gain knob it appears the LED light moves up on the scale but only after turning the knob approx halfway up. I have interchanged the chips from left to right channel with similar results and do not see any burned traces. I have interchanged the 3 LED chips also with no change. Any ideas are appreciated.

 

[VSAT88]

This may be stupid and it probably will not work but have you cleaned the gain controls ? The driver board that has the chips on it that you swapped side for side is it easy to get to ? Have you re capped that board ?

 

[vmaxman]

I am willing to pay for help in diagnosing the issue please pm me,

 

[grapplesaw]

I had this problem with a dual 500
Spent some serious time on it. I never finished the repair but isolated the problem to the High Z circuit

To make operational I pulled the four caps C1, C2 , C105 and C205 and one diode D5 from the center section of the board to eliminate that problem. Never replaced the ic dual op 4558 Z-1,2 or other transistor Q1 but suspect they are the issue or a blown diode in there somewhere
This circuit is useful for feadback like in a stadium setting but not something I need so never traced it out completely.

Not saying this is it but you could try it

 

[vmaxman]

To be clear remove the 4 caps d5 diode both 4558 ic's and Q1? thanks

 

[grapplesaw]

To be clear remove the 4 caps d5 diode both 4558 ic's and Q1? thanks

You can leave the Ic 4558 and Q1 In

 

[grapplesaw]

Here is the schematic of the high Z section

 

[grapplesaw]

If that clears it up then I will start to replace components in mine to find the bad piece

Having to suffer this hot spell for a while first.

 

[laatsch55]

Yeah, it does look unbearable..

 

[vmaxman]

Will do thanks for the info now translating that to the board is the challenge. I am assuming this is the LED board correct? So sorry to see you dealing with the tropical weather while the rest of us are handling
the winter weather even in southeast US. LOL

 

[VSAT88]

Southeast as in where ? Phenix City Alabama here.

 

[grapplesaw]

I am in Maui

That diode is not an led There are leads from the board to the led on the front panel.

 

[grapplesaw]

All of these parts ore on the main control board not the front panel

 

[grapplesaw]

Here is there locations. The two ceramic caps are in the general area

 

[vmaxman]

thanks Glen for the specific components. Will remove and touch base after. Enjoy your time away.

 

[grapplesaw]

Here is better layout. I guess I should use my glasses.

 

[vmaxman]

Glen all of the caps have already been removed. I did pull a leg on the diode and fired amp up same issue continues on the right LED.

 

[grapplesaw]

Ugh!
Anyone seen this in a 700 series ll?

The led meter circuit is the same for both the 700 ll and dual500

 

[Gepetto]

Did you swap the meter input feeds right to left to see if it is a noisy amp output or a defective meter board? It could be either one and you have to isolate it. If one of the amp channels is ultrasonically oscillating, the meter board will pick that up.

 

[VSAT88]

Did you swap the meter input feeds right to left to see if it is a noisy amp output or a defective meter board? It could be either one and you have to isolate it. If one of the amp channels is ultrasonically oscillating, the meter board will pick that up.

That is good info to know.