Fender Passport 500 Pro SMPS question

[JP-Stereo]

OK so the D615 line is only a starter supply ?

If SCR601 is the voltage reference adjustment, we should be able to verify that.
What if i power this without SCR601 to see the Vco tension ?
or
Can i use an external voltage to replace it ?

At this point this the most probable cause.

[x-pro]

What if i power this without SCR601 to see the Vco tension ?

can be turned on without it

[JP-Stereo]

It's the same with or without SCR601.
SCR601 removed the voltage after D615 is slowly ramping up to 14.9 vdc.
So i reinstalled it.
I see 15.9 vdc before D615 with D615 in circuit..

R632 is a little low at 72.06 k Ohm, R633 is right on at 99.66 k Ohm.
TH600 is set at 186 Ohm.

Just found an R682 (300 Ohm) in serie before D615, it did not figure on the schematic.
I measure 18.17 vdc at the anode of C616 without D615 and 17.0 vdc when D615 is there.

On the +15/-15 vdc rails from U600/U604, i measure +14.6 vdc and -15.5 vdc.
So the positive rail seem loaded even if i remove D615 or it's U600 ?

Only D612 left before looking at the supply side of EC28-18P.

[x-pro]

Take your time. We need to think this through.

[x-pro]

I measure 18.17 vdc at the anode of C616 without D615 and 17.0 vdc when D615 is there.

This, of course, is not very good. Any linear stabilizer needs a 3V difference between input and output voltage.
The input is 18V, the output is 15V. If the input is 17V, the output drops unpredictably.
Either something is loading the 15V line (such as large capacitors in the +50V secondary supply circuit), or the input voltage is low.
Are C683, C631, C646, C651, C647 suitable?

[JP-Stereo]

So i tested Off Board all these capacitors;
C683, C631 replaced because of lower value, C646, C651, C647 were fine.

I also replace D609 because it was unstable testing Off Board.

Now the 15VDC line is at 14.5 vdc after L605.
And the D612 cathode is at 17.3 vdc with over 5v of ripple.
The 50vdc bus give 27.59vdc.

[x-pro]

And the D612 cathode is at 17.3 vdc with over 5v of ripple.
.

Replace again with a new C616. With a good minimum ESR and for a temperature of 105 degrees.

https://static.chipdip.ru/lib/115/DOC001115623.pdf
The U605 chip has a reliable start at 16V, but the upper value of this voltage can be 17.5V.(Start Threshold).

[JP-Stereo]

If it wasn't the only problem, at least it was the last on this SMPS !
C616 was measuring 1.5uf !!!

Once replaced: We have 19.9vdc at C618, no ripple and 14.7vdc on the +15VDC rail.
U605 is alive and pulsing.

Most of all 101.99 VDC on the +50/-50 vdc rail.




It may be a good idea at this point to replace C617 also ?

How to verify the Class D amplifier for shorts or else before hooking it back ?
There is also the mixer...

[x-pro]

The probability of faults in the amplifier is low if there is no short circuit on the +/-50V supply circuits in the amplifier itself.

[JP-Stereo]

Everything is reconnected.
I have a 100w bulb in serie and it glow a lot.
In fact, i have a first surge at power up, followed by another a little stronger after a small pause, this is the Switching starting.
But after that the bulb glow stronger so i switched off.

No smoke signal yet, but idid not keep it on
I think i will measure the current draw.

[x-pro]

light bulb on the line voltage input?

[JP-Stereo]

Yes, like for testing a linear amp.
But if this beast draw more than 1 amp at power on, sure the bulb will glow...

Should i just power it on and see or there is a safer way ?

[x-pro]

Yes, like for testing a linear amp.
But if this beast draw more than 1 amp at power on, sure the bulb will glow...

Should i just power it on and see or there is a safer way ?

Check the transistors in the main power supply Q600 Q601.
Turn on also with the lamp, but without connecting the JA2(+-50V) connector to the amp.

[JP-Stereo]

Hi, Q600 and Q601 are brand new.
Since the +/- 50vdc is fine, they must work, no ?

JA2 disconnected, it's the same.
I think that about 1 amp is normal for this amp idling.
It's current draw is pulsing at about 3 second cycles, if i dare to let it on.

It look like a kind of protection in the PS that detect the resistance of the bulb...
I have ear about that somewhere, SMPS will not work with a current limit on the power line.
Could it be that ?

[x-pro]

May be