Problem with SoundSkulptor MP573 - Less than 24V at General Power Check

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leodalmaso85

Member
Joined
Feb 17, 2016
Messages
6
Hello to everyone!

I've just bought a SoundSkulptor MP573 and have a problem when I check the power.

In the MP573 Setup guide, on the 3rd point you must check for the general power of the Preamp. When I check without the output transformer I become 24,2 Volts, but when I check with the power transformer I'm getting way to less (13,6 Volts instead of 24 Volts).

Any ideas?
Thanks in advance!
Leandro
 
How many volts do you get between the lunchbox ground and TP2, without and with the output transformer connected?
How many volts do you get between TP2 and TP4,  with the output transformer connected?
Are U1 and/or U2 getting hot?
 
Hi! Thanks for the quick reply.

Between 0V (from the lunchbox) an TP2 without the otput tranformer= 9V
Between 0V (from the lunchbox) an TP2 with the otput tranformer= 1.29V

Between TP2 and TP4 = 8.38V

The U1 gets hot.
 
You have too much current flowing through Q6, fortunately limited by U1.
Check components value, solders and direction of:
R40 to R47,
C24 to C29,
Q4 to Q6,
T2.
 
Hi JPK,

I have checked everithing you say, and everything is in the right place and with a good solder.

It's possible that one component is defect? Maybe to much heat when I solder it?
 
Check that the ohm value on P2, between center pin and side pins changes when you turn the screw (with power off).

There are some DC voltage values in this PDF:
http://www.soundskulptor.com/images/debug/mp573b-DCvolts.pdf
Can you measure the values you get, relatively to TP2,  with the transformer connected (try not to stay too long with the power on) .
 
I can't measure the Resistence in P2 between the center pin and one of the side pins. The resistence changes the whole time between 37 and 40 MOhm, and does not estabilize.

The other measures relatively to TP2 are:
A: 0.19V
B: 9.57V
C: 0V
D: 9V
E: 3.6V
F: 8.37V
 
You may have a defective P2.
Remove it by heating the 3 pins at the same time (with a big blob of solder) and check it with your ohm-meter.
 
I removed it, and it seems to be that the component was defect. The middle leg was destroyed.
When I test , it works fine, but I'm buying the component on Amazon tonight and replace it on Sunday.
Thanks for the help and I let you know if everithing worked fine ;)
 
Hello JPK,

it's has been a while since I wrote, but now I'm happy!
I haved changed the P2 and now the preamp works nice!
Thank you very much!
 
Hello,

I had the same problem as Leandro, with the same strange measurement results and a hot U1. After following this thread and Jean-Pierre’s replies, I found that my problem wasn’t the P2, but a tiny solder bridge between R43 and R45 caused by a little bit of solder that made its way through the hole onto the PCB surface. So for anyone facing the same problem, check these parts as well.
 

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