Powerbass ASA1500.1Dx

[Dr Zeus]

In this amp, the power supply will not turn on correctly. Upon close observation, I find C312, a cap with 104 on it's back split in half and blown wide open (Two halves pointing straight up). I beleive these are 104Pf, or something of the sort. Please correct me if I am incorrect.

C312 is right next to the KA3525A

The KA3525A;
Pin 1: 0.013
Pin 2: 5.07
Pin 3: 0.026
Pin 4: 0.218
Pin 5: 2.117
Pin 6: 3.587
Pin 7: 2.1
Pin 8: 4.38
Pin 9: 5.52
Pin 10: 3.227
Pin 11: 0.015
Pin 12: 0.012 *
Pin 13: 12.28
Pin 14: 0.015
Pin 15: 12.29
Pin 16: 5.07

*One Pad from C312 is connected to Pin 12 of the 3525 and also Pin 4 of the KIA393P.
The other pad from C312 is connected to Pin 3 of the Kia 393P.

The C312 may be connected elsewhere, however I have not removed the board from the sync yet. If its just the C312 that is bad I can likely replace it without removal.

Thanks in advance

[Dr Zeus]

KIA393P

Pin 1: 10.32
Pin 2: 2.53
Pin 3: 5.00 *
Pin 4: 0.014 *
Pin 5: 10.60
Pin 6: 2.528
Pin 7: 3.668
Pin 8: 5.07

[Dr Zeus]

C312 is also connected to the Anode of D 308 which is testing OK in circuit.

[Perry Babin]

Can you post a photo of the area of the board where the cap is located?

[Dr Zeus]

[Perry Babin]

You're right. It's marked 104.

Find the diode that has its anode connected to pin 10 of the 3525. Is it leaky or shorted?

[Dr Zeus]

Thats D306. It was measuring a little tough on the board so I lifted up one side for checking. It appears to be leaking as it measures millions of ohms in both direction. It has markings, its a 16v ZD.

Can I use a 1N4744, 15v Zener?

Also for C312, is that 104pF or 10,000pF / 10uF?

[Perry Babin]

The Zener is part of the over-voltage protection circuit. The 15v would simply make it shut down at a lower voltage.

The capacitor is a 0.1uf.

[Dr Zeus]

I see. I installed a new 104 cap. Here is also a decent guide I found on cap markings: Capacitor Code Guide

I put the 15v ZD in, plus the cap and got the amp powered up. Can I presume, that the 15v/16v ZD is measuring B+ voltage, where the cutoff point either 15v or 16v? That is interesting to say the least.

[Perry Babin]

Those capacitors are marked and are read like resistors. The Resistors and Capacitors page of the DVD will tell you most everything you need to know about reading the values of various types of capacitors.

The zener begins to conduct when it's breakdown voltage is reached. From that point, it begins to pull the voltage on pin 10 up until the voltage on pin 10 reaches the threshold to shut down the IC.