Fender Passport 500 Pro SMPS question

[x-pro]

Let's be clear. At the moment, the U605 is powered by 18V ?
SCR601 on the board.
D631 is off the board.
R636 is off the board.
What is the voltage at b Q604 ?
Check the rating of R638.

Power supply voltage and b Q605 voltage to measure to the nearest decimal place.

[JP-Stereo]

Hi, thanks again...

U605 receive 18.008vdc in CV mode from a power supply.

SCR601 on the board.
D631 is off the board.
R636 is off the board.

b Q604 = 17.338 vdc
R638 = 99.72 kohm
b Q605 = 5.161 vdc

Pin 6 is pulsing to 15 vdc.
And the resistor on Pin 6 begin to heat seriously...

[x-pro]

Restore all connections and solder all "native" elements to the board. Remove the resistor from pin 6 of the U605 chip and connect the chip output to the C655 input according to the diagram.
Connect the mains voltage via variac or in series with a 100W incandescent lamp.
Evaluate the operation of the power supply by the output voltages.

[JP-Stereo]

Hi, it's done and here are the readings at the main connectors.
The amp and mixer are disconnected.

JA1
Pin 1 = 0.0002 vdc
Pin 2 = +14.947 vdc
Pin 3 = gnd
Pin 4 = -15.038 vdc
Pin 5 = 0.0001 vdc
Pin 6 = +47.844 vdc
Pin 7 = gnd
Pin 8 = +8.054 vdc

JA2
Pin 1 = +13.8xx vdc
Pin 2 = gnd
Pin 3 = gnd
Pin 4 = -13.8xx vdc

The Protection lines and Mute line (Pin 1 and 5) are at 0 vdc.
No pulse at U605 pin 6
Still no +50 and -50 vdc...

[x-pro]

What's the voltage on C676?
Did you put the R634 resistor back in place?

[JP-Stereo]

Yes R634 is there, in fact i never removed it.

C676(+) is -0.205 vdc (this line is dead)

D633 pass the diode test.

At the junction of D600/D602 i read 117 vac (60hz) and 157 vdc as if it wan't a fullwave rectfier..?

[x-pro]

If your mains is 110-115V, you need to short CN601.

[JP-Stereo]

Absolutly, i installed a jumper and i double checked the continuity between the traces of the board.



It must be something in this area.
Q600 and Q601 have been replaced.
Most of these diodes have passed the diode test.
I will check the last ones,

[x-pro]

Maybe one diode in the BG600 is broken.

[x-pro]

At the junction of D600/D602 i read 117 vac (60hz)

AC???

[JP-Stereo]

I desoldered BG600 and the 4 diodes test OK, no shorts, no open, similar voltage drop.

The previous voltages were from my multimeter,
CN601 bring one side of the AC line on the positive DC rail through R601.
What is the waveform to expect at (+)C600 ?

The scope detect a 60hz sinewave riding on a DC base of 15v with a probe at 10X.
That mean 325v of sine on a 150 vdc base, so i have to offset it in order to center the sine.

[x-pro]

The scope detect a 60hz sinewave riding on a DC base of 15v with a probe at 10X.

I don't get it.

"What is the waveform to expect at (+)C600 ?"

There should be a constant voltage of 310-320v. There may be slight ripple. Measure against the minus of C630.

[JP-Stereo]

OK, sorry i made a grounding error.
The ACGND was mistaken for the AUXGND...
There is also a HCGND a EARTH and the standard GND...

So really this is the V+ line.


Offsetted to the bottom of the scale at 50v/div, no AC...

I took the (+) on one end of R614 and the ACGND on the other end of R601.
Measured with a floating scope.

So this part look good till at least D602...
All the diodes are passing the diode test.
All resistors, capacitors and inductors have passed the basic verification on or out of board if required.
I have removed MOV600 and 601.

The problem seem to orbit around the starting supply of U605.
The native power supply only provide 15.345 vdc after a few minutes.
The supply start at 13v and ramp up to 15.345 vdc after a few minutes.
Still not enough...

[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.

Is it safe to remove R629, R632 and/or R633 and power it up ?
Is there some control line that are essential to safe operation there ?

[x-pro]

You can try removing R629, but probably Q604 will be turned on from the Z608 D629 R631 circuit and the b-e junction of the transistor itself, if the Z608 is defective or "leaking".
Exclusion of R632 is equal to exclusion of diode D631. We have already done this.