PeeCeeBee V4 GB!

[shaan]

Hello Shaan, I still haven't received the shippement. could you please send me the tracking number?
Thank you!

Sent to PM.

 

[delange]

Sent to PM.

Message received; thank you Shaan!

 

[nanakos]

Hi Shaan
i have just assembled 2 module but i have problem.
I have used 42v with all mods (mje340-350,mur160.330Ω)
The multimeter on R29 shows 750mv and after 2 minutes i had smoke from R5.
All the construction seems to be ok.
Have you any idea?

 

[shaan]

Hi Shaan
i have just assembled 2 module but i have problem.
I have used 42v with all mods (mje340-350,mur160.330Ω)
The multimeter on R29 shows 750mv and after 2 minutes i had smoke from R5.
All the construction seems to be ok.
Have you any idea?

R29 should show less than 750mV. Could be faulty BJTs or oscillation. Can you upload a couple pictures?

 

[nanakos]

Both modules have the same behavior

 

[nanakos]

The mosfets are EXICON

 

[shaan]

Both modules have the same behavior

The MOSFETs are probably fine.
What small signal bjts are you using?
Do the LEDs light up when module is powered?
What is the LEDs' voltage rating?

 

[nanakos]

I'm using MJE340 and 350 and the leds light up

 

[shaan]

I meant the BC transistors.

 

[nanakos]

BC 556 BC547 all matched

 

[shaan]

Remove the board from the heatsink, check all the BC transistors between base-emitter and base-collector with meter set to diode test mode. Also check C5 and C6 whether they are leaking DC, meter set to diode test mode.

 

[nanakos]

I have check all of them with transistor meter and they are OK.
Is there a possibility that it is wrong the bc547 istead 546?

 

[shaan]

As long as the small bjts and c5/6 are okay the resistor should not burn. The high VAS current suggests the input transistors are passing a lot of current. The CCSs limit current via the 1K resistors in series. If the 100R is burning that means the current is coming from ground, possibly via faulty C5. That's why I asked to test the 2200uF.

BC557 has maximum rating of 45V. So 42V is a little too close to safe operation limits. Try replacing them with 556.

 

[nanakos]

547 no 557

 

[shaan]

Ratings same for both 557 and 547.

 

[nanakos]

I'm going to replace all bjts because the 2200 caps are ok

 

[nanakos]

Hi Shaan
I pulled out the bjts from one module and found 2 fault 547 and 1 556.Have you any idea why?

 

[shaan]

Which place were the faulty BJTs in?

The 547 may have failed due to overvoltage and may have taken 546 with it due to passing high current if it failed in short circuit mode.

 

[nanakos]

I changed the bjts with new and 546 unfortunately not matched but tha amp came to life with no problems and very stable.With 42v tell me Shaan what vas and what bias must be?

 

[shaan]

You can set vas bias to 350mV in R29/30.