m1989jmp 10/9/2017 3:33 AM
Vox Pathfinder 15R DC on output
Hi all,

this little amp was on the other end of amp-to-amp-plugging catastrophe. I've fixed the Ashdown MAG300 bass head with your help.

I'm measuring -20VDC on the speaker out; is it safe to say TDA2030A is toast? Also, later today I'll test the diodes separating rail voltage from output too.

How do I make sure the mentioned opamp is indeed faulty?

[ATTACH=CONFIG]45242[/ATTACH]
 
Mick Bailey 10/9/2017 8:54 AM
It probably is toast. I'd remove it and check to see if the voltage disappears and also to make sure there's no DC on pins 1&2. For me they're cheap enough to replace by elimination and balance of probability. While it's removed you could check between the negative supply and output pins to see if it's low resistance. Unless they blow apart they usually fail short.
 
m1989jmp 10/9/2017 9:06 AM
Quote Originally Posted by Mick Bailey View Post
It probably is toast. I'd remove it and check to see if the voltage disappears and also to make sure there's no DC on pins 1&2. For me they're cheap enough to replace by elimination and balance of probability. While it's removed you could check between the negative supply and output pins to see if it's low resistance. Unless they blow apart they usually fail short.
Will do, thanks a lot. Yes, they're 2€ in my local electronics shop so it's a no-brainer.
 
m1989jmp 10/10/2017 1:47 PM
Quote Originally Posted by Mick Bailey View Post
It probably is toast. I'd remove it and check to see if the voltage disappears and also to make sure there's no DC on pins 1&2. For me they're cheap enough to replace by elimination and balance of probability. While it's removed you could check between the negative supply and output pins to see if it's low resistance. Unless they blow apart they usually fail short.
Turns out the diodes were fine after all. Popped a new TDA2030A in after I measured 0VDC on speaker out. The amp now works as it should, no hum.

No DC on pins 1 or 2. Can I ask why did you ask me to measure it? To make sure coupling caps were ok?
 
Enzo 10/10/2017 6:40 PM
If there was DC voltage on the input pins of the TDA2030, and I mean DC voltage coming from the circuit board, then that can cause DC on the TDA2030 output. SO we pull the 2030 and then check to see if there was any DC voltage at the input pins. If not, then the DC is the fault of the IC.