Homebrew PCBs

Actually, I sprayed my PCB AFTER I tested it by using a 9V battery 
set the signal input to positive and negative.  The booster responded 
correctly and the polarity of the output was correct in both cases.

The lacquer I sprayed on the PCB is a clear coat, which doesn't 
contain any pigments.  Therefore according to your comments, this 
shouldn't affect the circuit.  Am I coorect?

Now, I suspect that the positive voltage on the TxD pin on the RS232 
port of the ATX motherboard may not be high enough to drive the 
signal transistor (see the booster.bmp in the booster directorey in 
the files section).  Therefore I swap the positions between the 390R 
and the signal transistor on both sides, so that the signal 
transistors can be activated at a low voltage (booster2.bmp).  Do you 
think this can solve the problem?

Mark


--- In Homebrew_PCBs@yahoogroups.com, Stefan Trethan 
<stefan_trethan@g...> wrote:
> i'm sure it isn't the laquer.
> also the metaloxide paints should isolate.
> maybe there are some "metallic" look paints which conduct but....
> 
> it is not very wise anyways to cover up the pcb before you tested 
it.
> i never spray mine at all and if not touched with your fingers they 
won't 
> oxidize too much at room conditions.
> 
> you should never assume any circuit working on the first try.
> you can only assemble a board fully and spray it without testing 
when you 
> have already made a second working one before.
> 
> but take the laquer of for your convenience when soldering to 
repair it.
> take any solvent and brush. if you have plastic parts (connectors 
etc) on 
> the component side don't wet them with solvent.
> it may dissolve them.
> 
> then get the scematic and test every function.
> assuming you have no scope this makes it necessary to get all "nice 
and 
> slow".
> 
> fast rs232 voltages you can't test with your meter.
> 
> if you provide the scematic somewhere maybe one may have a look on 
it and 
> tell you what even if this is mostly a pcb hardware
> manufacturing not debug board....
> 
> hope you get it right....
> 
> stefan