[BlizzofOZ]

I totally screwed up the pcb on my first attempt at a Mini3. So I ordered some more parts from Amb to try it again.

So I'm at the point of doing the Quiescent current check. I have the battery hooked up to the positive terminal, leaving the negative free.

I put my meter on 200mA (manual range), turn on the amp and place the black probe on the neg battery terminal and the red probe on the neg post on the board.

My meter read are some in the range of 97.3 Is that correct? My first attempt, I could have sworn I was in the 24.x range.
According to Amb's site, I should be getting 25mA (high performance) and it seems I'm four times as much.

I've clean the pcb throughtly and triple checked for bridge and such. Last time I didn't have a good soldering point on the battery post. Checked that and all looks good.

Any suggestions on where to look?

 

[pdupiano]

Do the other tests first. But it looks like there might be a short some where. Unfortunately after that.. the only possible cause might be a fried chip.

 

[BlizzofOZ]

Stupid question:
How can a chip get fried if you haven't hooked the battery up completely?

Can you fry a chip by doing the Quiescent current check, where the battery is only hooked up to the positive terminal?

 

[ShinyFalcon]

You're basically forming a bridge with the multimeter when doing the current check. Did you turn on your amp while doing the current check? The amp if working should work exactly like an amp while you're doing the check and while the battery's installed.

 

[MisterX]

Youre' right.



It's a stupid question.
The battery is "hooked up" to both terminals through the amp meter.

Edit: your question was already addressed by ShinyFalcon, sorry about redundant reply.

 

[BlizzofOZ]

Stupid question to you maybe, but if asked it usually means the person is not quite sure of the answer...

What can cause a chip to fry? Is there a way to test if it is fried?

 

[MisterX]

I was merely reaffirming your suggestion that it was a stupid question.

Quote:

Is there a way to test if it is fried?

The DC offset is a fair indicator.

 

[BlizzofOZ]

Thanks MisterX, I'll test the DC offset next.
I didn't want to continue testing for fear of screwing something else up.

Again though, what can cause the op-amp to fry upon first power up if there are no bridges?

 

[ShinyFalcon]

If there's static, it can certainly kill anything. There's also overheating by soldering, the possibility that the part was defective in the first place, defective PCB, and lastly user error. We won't know what's wrong until you tried all the tests. The opamp may not have fried, maybe it's the rail splitter.

Try the diodes and see if they pass the diode test. Use your multimeter's diode test, when you place the probes on the diode's lead you get two readings when you place the probe both ways: 0 and any number. If you get two numbers not zero, then the diode is bad.

 

[BlizzofOZ]

Gotcha... Don't jump to conclusions.

Ok, I've never done an DC offset test before with my meter. Do I switch it
DC voltage? The symbol is V straight line on top and dotted line on bottom? Lowest setting I have is 200m.

 

[ShinyFalcon]

Yes, that symbol is for DC. I use 200m for millivolts. 20 goes up to 20 volts, 2000m goes to 2 volts, and 200m goes up to 200 millibolts.

 

[BlizzofOZ]

Ok, here are my results:

DC offset
Set meter to 200m DB Voltage and get the following:
Black probe on IG and red probe on OG = 0.2
Black probe on IG and red probe on OL = 0 > no value
Black probe on IG and red probe on OR = 0.4


Diode test
Set meter to diode testing
Forward Bias?
Black probe on the side stripe and red probe on other end. For all 3 diodes, I get one value that range in 75x to 76x (seven hundred range).
Red probe on the side stripe and black probe on other end. For all 3 diodes, I get no value.
I believe the diodes are ok, based on what ShinyFalcon is saying, correct?

 

[ShinyFalcon]

What's left is the rail splitter test. If that fails, we know that's the problem. And there's also the battery charging test too.

Edit: Removing bad advice

 

[BlizzofOZ]

So the DC offset is ok? I thought it needed to be in 5mV range and I'm getting .2, 0, .4... Not disagreeing with you, just trying to understand how it works.

Rail Split test
I believe this is good.
Set to 20V and I get 7.45 on V- & V+ and 3.70 on V- & IG

I put the battery, turned on to low volume. I get a very audible click when turned on. I get sound in Right and not in left.
Another very audible click when turned off.

 

[ShinyFalcon]

Hmm let's try measuring DC for left again, this time go up the scale (2000m, 20), maybe there's a significant offset on left channel and it went off the chart for 200m.