Fender Passport 500 Pro SMPS question

[x-pro]

How did the "epic end"?

[JP-Stereo]

It's not finished yet !

I've changed the D615 without reaction.
I've recheck the IRFP460's, they are latching and opening well.

On the main PS when everything is installed i have a pin 7 Vcc of 15.35vdc, that's not enough.
With an external PS of 16.36Vdc and higher it's pulsing, when D31 and R36 are removed.

There is something around D31 and/or R36 that load the Vcc line.
Or it's a second problem in the Ref circuit, that load the IC from the Ref side.

It took me some time because i messed with U603 after resoldering some pads.
Because of too big solder, it sparked and i had to hunt for a ICE2B365 a source a new one, beside a 0.33R resistor (R641)
Sh__ happend...
I am there now.

The main Vcc problem must be solved first i figure ?

Thanks for following.

[x-pro]

We'll wait for the Vcc to recover.
Forward on the pitchfork, like raiding a liquor warehouse.

[JP-Stereo]

Funny, but no progress...
I have the proper voltage if i unload R615, so i must find the extra load on this line.
While on the main PS, do you think it's risky to power up this unit without D608 ?

I am trying to eliminate a subcircuit at a time til the voltage get up...

[x-pro]

D608 is serviceable if it is in good working order. There is no point in removing it.

[x-pro]

I have the proper voltage if i unload R615

All elements around the U607 must be in good working order and must match the rating.
R615, R648 must not be removed. They are responsible for stabilization of SMPS output voltage on U603.
If during operation of this power supply the output voltage of D615 is less than 18-20V, then check all capacitors for ESR on the secondary side - (C633, C616, C617, C644, C645, C648, C646).
This is not an easy job, this device is not a flashlight on a light bulb. Making sure they are quality parts is a must.

[JP-Stereo]

I will verify those components, but why the voltage is there when i unload D615.
You do not think that something load that line ?

[x-pro]

What does unloading mean? What elements are excluded in this case?

[JP-Stereo]

" Hi, i have lifted the D615 cathode and read the voltage ---> +18.585 vdc, enough to start U605, so something else is loading this VCC line to 15.345 vdc..."

[x-pro]

What is connected to pin 6 of U605 ?

[x-pro]

Repeat the test again:
Is D608 serviceable, is it soldered correctly?
Are C653, C654, R626, SCR601 of good quality?
These parts can be temporarily desoldered. Or remove them one at a time, checking for voltage rise.

[JP-Stereo]

On U605 pin 6 i only have C655 and D627.
D608 test OK, 0.499 drop, wired from U608 toward D615.
C653 test 101uf, i will have to remove one to test the other.
R626 4.56 kohm.
SCR601 is new.

I will double check them one at a time, C654 first...

[JP-Stereo]

Hi, C654 measure 109nf offboard.
For replacement, i always use Nichikon, CDE, Kemet, etc.

Since SCR601 is somewhat problematic to test, i decide to replace it but never found a source.
This one look difficult to replace if no subtitute are knowed.
So the original is still on the board, untested.

About U608, since D608 test OK, is this 5v regulator can mess with the Voc, and why is it there first, on a 18v line ?

I figure that removing sequencially R629, R632 and R633 if possible, will show what is loading the Vco ?
Only D608 left or is it what's supplying D615 that is too weak ?

[x-pro]

R632 and R633

These resistors are large in rating to load the power supply in some way.

[x-pro]

About U608, since D608 test OK, is this 5v regulator can mess with the Voc, and why is it there first, on a 18v line ?

If D608 is good, has no leakage, and is soldered according to the schematic, then U608 cannot affect the 18V line, to reduce it. It can increase it. From U608 output 20V, minus 1V to D608, and the line should get 19V when the main power supply turns on.