1

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 14, 2024, 04:17:15 PM »

Yes, they look pretty good now:

TP2: -9.1
a: 2.6
b: 4.0
c: 22.5
d: 13.5
e: 2.0
f: 12.9
g: 0.9
h: 4.0
i: 0.4
j: 3.4
k: (cannot measure, it's plugged)
l: 2.9


Mmm, could it be just bad luck with that blown cap? Or do you think there's another issue? Just FYI I have another MP573 working just fine in the same lunchbox, so not sure why it happened

2

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 11, 2024, 11:51:10 PM »

I changed the cap, now the measurements:

TP2: -9.1
a: -6.4
b: -5.1
c: 13.4
d: 4.4
e: -7.1v


I unplugged the unit at this point, since the measurements seemed bad. Now TP2 seems fine, but not the others. If you need some other measurement please let me know, the card is over the table now.

Thanks!

3

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 07, 2024, 06:01:28 PM »

Do you mean to replace the regulators? I don't have spare parts for that, and surprisingly there's no LM7909 on mouser. Do you suspect the 7909 and diode burned out? Why this happened? Could be caused by a bad input?

- R27 is 7.5 Ohm.
- Both diodes seem funny. They don't conduct, Just a small beep and then I see the voltage drop between its leads (around 0.56 Vdc). If I reverse the meter, they don't conduct but I see voltage drop, in reverse. So I guess both are dead.
- As per the regulators, I don't have a spare LM7909 nor LM317T. I'm checking mouser and they don't have it, oh gosh I'll have to buy them in China?

In any casse thanks for the support JP

4

MP573 Microphone preamplifier / Re: Blown capacitor

« on: August 06, 2024, 09:43:14 PM »

Thanks for the support! Here goes the measurements:

TP2: 13.1
A: 12.8
B: 14.2
C: 15.3
D: 13.7
E: 13.1
F: 13.2
G: 12.8
H: 14.2
I: 13.1
J: 14.6
K: (it's plugged, cannot measure)
L: 14.1


I saw the values I read are very different from the expected ones. no clue why.

5

MP573 Microphone preamplifier / Blown capacitor

« on: August 05, 2024, 11:11:32 PM »

Hello, my MP573 died a few weeks ago. I opened it and discovered the C13 cap was blown and leaked. I attach some images at imgur:

(https://imgur.com/a/wGRzk3T)



Apparently there's no cold solder joint. I don't know it this was just a bad luck cap death, or if it hides something. Maybe the L7909 is damaged. I can try to replace the cap, but the one I have is shorter, and most likely not low ESR. Any advice on how to repair it is more than welcome.

Thanks.