Hi friends, im repairing my MAX 7.2. It had AC/DC IGBTs blown, i replaced them, checked optocouplers, and driving circuitry it looks ok. I also checked the UC3845 wich works(Generates about 95kHz). But it still gives F09 and the fans keep working at max speed. Can someone help me? If im correct, the softstart board should be on top of the MPPT PCB. Am i right? If yes is here some reversed schematic? I also checked semiconductors on the softstart board but everything looks ok. Also on main PCB all transistors and diodes are checkd. Is the maximum fan speed dependend on the F09 error, or is the CPU thinking of some NTC overtemp failure and so it does not enable drivers?

On 2023/12/07 at 4:50 AM, sp22 said:

I also checked the UC3845 which works(Generates about 95kHz).

That seems too high a frequency to me. @BritishRacingGreen, can you confirm?

[ Edit: I was also thinking of the KA3525, sigh. ] 

On 2023/12/07 at 4:50 AM, sp22 said:

But it still gives F09

Have you checked for a short on the DC bus?

On 2023/12/07 at 4:50 AM, sp22 said:

is here some reversed schematic?

Yes, BritishRacingGreen has been doing a great job. For example, the DC-AC converter section is covered here.

On 2023/12/07 at 4:50 AM, sp22 said:

Is the maximum fan speed dependent on the F09 error, ...

The fan speed it set to 100% on power on; the DSP has to turn them off. So often fans running full blast means that the control board isn't working  or even plugged in. But you mentioned fault code 09, so the DSP must be running. It might just be that the DSP would turn off the fans when it gets to a part of the code that is never reached because of the fault.

On 2023/12/07 at 4:50 AM, sp22 said:

or is the CPU thinking of some NTC overtemp failure

I don't think that's likely. But that's just a guess.

Edited December 9, 20232 yr by Coulomb

On 2023/12/07 at 3:41 AM, Coulomb said:

That seems too high a frequency to me. @BritishRacingGreen, can you confirm?

That is too high, yes. 

EDIT : apologies I was confused with the KA3525 PWM output. 

Yes 100khz is about right. The period for the main SMPS UC3845 is measured at about  10.8 uS by me in the past, so that equates to just short of 100khz. Furthermore, duty cycle can be very low, as low as 800nS.

See oscilloscope below:

 

Here is an example of the output of the secondary side of the flyback transformer. 

The 'on' period here is typically 2 to 4 uS when the rail outputs are under load. 

This output is also distributed on the main board as an ac input for dc-dc isolation supply xformers. 

Edited December 9, 20232 yr by BritishRacingGreen