Martin Logan SL3 crossover issue

[MickyP]

Hi

I posted below on the Martin Logan forum and was advised to try here. Essentially I have one panel not delivering high frequencies; it isn't the panel (they're quite new) and has been identified as the crossover/power supply. I have a techie who has done some diagnostic work and has asked some questions, below.

If you have any thoughts please chip in.

Techie questions:

1. The EHT seems to be working and measures 2200 volts which is the same as the working board
2. I have swapped over the 4 channel Op amp and that is working
3. I have tested the high value electrolytics C3, C8, C5, C6 they are all OK
4. I have replaced the triac - that is OK
5. I have tested the transistors Q2 and Q3 – they are OK
6. When powering up the LED lights OK but goes out after about 2 minutes

I would welcome some useful information such as:-

1. A detailed description of the operation of the circuitry
2. A test-point map with expected voltage readings
3. Suggested probable fault given the info 1 to 6 above

ML want £309 for a board which 'usually solves the problem'. Am I right in thinking as it's the power supply board only, I don't need two boards to match speaker outputs?

Thanks in advance for anything you can offer!

Mike

 

[Andersonix]

The crossover is a separate circuit from the HV PS (120VAC-60Hz version attached).

To me it sounds like the Music Sensor is not working right, as in either not triggering with input signal, or not staying on after triggering. The MS section starts top left, but I don't remember how it works. Is it the ratio of two caps or two resistors to set the timing/sensitivity? There was an old thread around here that described it...