duende

Soundtrack sequel psu breakdown
« on: October 10, 2020, 11:32:12 AM »
Hi,

After a PSU capacitor recap on the Seqel 2 psu board the + 17v and the 5V don't work. All the components are ok visually.
The transformer secondary  are 24v, and after the diode bridge i mesure 33v and 0V. I don't understand how work the IC L4977A.

I mesure 33v at D1 negative and 0V after the +.

Have you have some info on this circuit ?

Thanks.


duende

Re: Soundtrack sequel psu breakdown
« Reply #1 on: October 10, 2020, 11:41:42 AM »
Better view...

Khron

Re: Soundtrack sequel psu breakdown
« Reply #2 on: October 10, 2020, 03:50:09 PM »
What exactly do you mean by this? ???


I mesure 33v at D1 negative and 0V after the +.


For what it's worth, the datasheet can be found here:
https://www.mouser.fi/datasheet/2/389/cd00000084-1795415.pdf
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

pucho812

Re: Soundtrack sequel psu breakdown
« Reply #3 on: October 10, 2020, 07:16:54 PM »
are you sure you have the correct polarity on the capacitors?
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

duende

Re: Soundtrack sequel psu breakdown
« Reply #4 on: October 13, 2020, 06:29:41 AM »
Hi,

Yes the polarity is correct... And the -17V is ok .

I mesure 33V at D1/R2 and OV after D1/C2.

I have changed the diode bridge the last week but the problem is the same.

Sometimes when and i turn up the power the 5V led are illuminated during 1 second, maybe a capacitor charge ?


pucho812

Re: Soundtrack sequel psu breakdown
« Reply #5 on: October 13, 2020, 06:27:29 PM »
shotgunning parts is not a good approach.  having the -17 volts as o.k.  and the other not o.k. could still be related to caps.  You also may have a shorted transistors, a shorted resistor or any number of components that have failed.  You may even have a failed  IC L4977A. hard to say. The Schematic is hard to read.   the  IC L4977A looks to be a regulator. The pin out was provided. Should be easy to check if that is not working.  However if you  are not sure about it, I would take it to a repair shop. We doin't want you to hurt yourself to cause further damage. 
You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is.

duende

Re: Soundtrack sequel psu breakdown
« Reply #6 on: October 15, 2020, 11:05:38 AM »
Thanks everyone, i did find a bad solder and no connexion between the two layers...

The PSU work fine.

Thanks.


 

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