Help needed with new amp9b

[hybridfiat]

I get a high pitched whine in channels 3 and 4 when the amp is powered up.
Ive double checked the soldering and cant find any components round the wrong way or bridged.
Has anyone any suggestions?

Entia non sunt multiplicanda praeter nessitatum

[Havoc]

Are you sure you havent soldered a diode backwards? Also check for solder bridges.

[hybridfiat]

Ill double check. Ill take some pics tonight and post tommorrow

Entia non sunt multiplicanda praeter nessitatum

[V-bro]

Probably this is not due to the diodes, but the small yellow caps are rather suspect. I must also ask you what power supply is used? And I am curious to the DC voltage on the outputs....?

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

[hybridfiat]

Ill try and check the DC on the outputs today. Im at work so I may not have time. What is meant by suspect yellow caps?

Entia non sunt multiplicanda praeter nessitatum

[Havoc]

I had a mate solder on a diode backwards on the amp6 and he got a loud noise/whine when input was connected, but off.

The small yellow caps are those you solder to the legs of the 4100 chip and elsewhere on the bottom and top.

Maybe also supply pictures so V-bro and other powerusers can help you better?

[hybridfiat]

Ive taken a couple of pics. The diodes are correct.
I dont think the caps are the problem unless I got them mixed up.
Im thinking it may be the diodes closest to the chip pins that are bridging.



Entia non sunt multiplicanda praeter nessitatum

[V-bro]

High pitched noise is usually oscillations due to lack of power supply power. But that would have to be WITH signal connected. When it oscillates at idle it can be caused by a short for instance.

Can you shoot a picture of the back of the chip, I'm particularly interested in the solders of the big row of small yellow caps. What usually happens is that people cut the leads not short enough and they touch the chip pins... These leads should be cut EXTREMELY short!

Another possibility is still the diodes, have you held the board against a powerful light to "peer" through the board. This is a nice way of "X-raying" the board to find shorts... Have a good look at the chip pin/diode solders section....

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

[Scratchy]

Wow, I'm impressed Steve!
Your's is one of the few boards which have been posted here that is cleaned immaculately.
It is so clean you could eat off it! Nice job!
It makes it much easier to see any potential flaws in the soldering.

Have you taken a magnifying glass or a loupe to the board to inspect some of the solders?
You'd be amazed at what you can see with a good loupe:
I've posted several photos taken with my digital camera through a 15x Loupe:
http://www.41hz.com/Forums/topic.asp?TOPIC_ID=1854
http://www.41hz.com/Forums/topic.asp...55&whichpage=3

Not sure if you've seen this or not, but I posted how to check your diode connections with a multimeter in V-bro's Diode Soldering tutorial in this forum:
http://www.41hz.com/Forums/topic.asp?TOPIC_ID=1987


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

[Havoc]

I would try soldering some more on the diodes. As far as I can see there is several diodes which might not have a good connection. A good connection is when the solder spreads to the copper pad and makes a concave solder joint. Try heating the board first with the tip of your iron, before heating the solder and diode.

But listen to V-bro among others as he knows what he is doing

@ V-bro
I sometimes have problems when making the legs very short as the solder won't flow trough the hole and up the leg on the cap side because of the cap coating. How do you solve this?