shorting amp9B

[nrgizerbunny]

Hi all, I just finished soldering up my AMP9B and have spent the last 4 hours trying to find a fault. I've got some short somewhere but don't know where it is. the resistance after the diode is 0.39R!! anyone know where to start? I had a quick look over the whole board and couldn't see anything obvious.

[V-bro]

Can you post a good picture of the bottom (especially round the chip-pin area) I have had one board with a shorted PCB trace, perhaps I can detect the short for you

------X-max. can be several meters on any driver, too bad it can be done only once...------

[nrgizerbunny]

Hi VBro,

see if these are any good:






its been driving me up the wall!

[V-bro]

Hi, if you look at the diodes, the one on the top far right is near the suspect pin (pin 14 of the chip) That's where one of my amps had a short between + and ground...

I must also ask if you are sure the solders of your diodes aren't touching the chip pins?

It may help to find the problem by checking what pins have ground or pos voltage and hold the board against a strong lamp to "look through" the board (as sort of x-raying it...)

------X-max. can be several meters on any driver, too bad it can be done only once...------

[nrgizerbunny]

Hi V Bro,

many thanks for doing that for me, i shall remove all the diodes and then check. its doing my head in! thanks again.

[Scratchy]

You might want to also review V-bro's diode soldering tutorial post here:

http://41hz.com/Forums/topic.asp?TOPIC_ID=1987

I posted some instructions & photos on how to test the diode paths using a multi-meter with a diode test function.

***If it was easy, everyone would be doing it***

[nrgizerbunny]

hi guys, a bit of an update. i removed all of the diodes on the bottom and cleaned up the joints. Still got a short somewhere. I'm not sure where. anyone got any better suggestions?!

Looking at the board it looks okay but wondering if its possible i could have a defective one.

[V-bro]

There aren't too many parts connected to the power rails, so if you have the schematic you can make a suspect list and remove parts one by one (I can't think of a better idea from here).

I can only say that my advise for other builders is measure the resistance of the board on all connections first. Especially the power rail after placing the three big SMD diodes (after these are connected most of the positive power connections on the board are connected) Or measure between ground and "after" these diodes....

This won't help you much any more Nrgizerbunny, I sure hope your chip isn't damaged...

Also for other builders I advise to measure the power rail resistance just the chip is put into the holes, when you press it in gently it'll probably make enough contact. This way you can be sure the chip isn't damaged in the first place (damaged in the sense of shorted, of course you can't exclude other types of damage)

------X-max. can be several meters on any driver, too bad it can be done only once...------

[nrgizerbunny]

hi V bro, i've emailed support to see what they say. I didn't apply any power to the board so i *hope* my chipset is okay, having said that to get the chip out i think i need to cut the pins. so i'm probably screwed. i've started taking various components out. I'm 99% certain that there are no solder joints that have over run, i suspect there may be a component that has internally failed and shorted internally?

[Scratchy]

I doubt support will be able to help you (if you get a reply).
If anyone can help it is V-bro, he has built more AMP9s than anyone else in the world.
As a matter of fact, 41hz uses V-bro to assemble and test their new amp boards and designs.

I suggest you clean the board thoroughly as per this video - http://tangentsoft.net/elec/movies/tt05.html
Get yourself a good magnifying lens or loupe and inspect all solder joints closely.
This goes a long way in confirming all connections are "up to snuff".

***It's so easy, everyone should be doing it***