Doepfer

Hi Coleman,

The function of Q1 is very simple, it converts the low-level (5V) 
gate signal coming of the main processor and converts it to a 12V one 
to send out on the bus. It is hard to imagine anything being 'wrong' 
with this, *unless* for some reason there is already 12V on the gate 
line on the bus - if the 190 then commands a 'gate', Q1 will have 12V 
across it with NO current limiting, which probably implies melted 
transistor and blown fuse (which sounds pretty much like what 
happened). Thus you need to establish whether there *is* any voltage 
on the gate line when the 190 is disconnected - I suggest double-
checking that all other modules are connected to the bus properly, 
red stripe on ribbon 'down' at both bus and module ends, and none 
displaced by a pair of pins upwards or downwards.

I expect that the AD5 is on correctly, but check anyway (red stripe 
down, 'up' arrow pointing upwards, and also not displaced by any 
number of pins). All the 'programming' LEDs are driven by the 5V 
supply, and you say these light OK - unless of course there is some 
other voltage, like 12V, on the 5V bus..).

If you have a meter that will help (but take care poking around with 
the mains on....).

Whether there is any more damage to the 190 other than the blown 
transistor is hard to say - once you've isolated the problem, 
replacing the transistor and trying again is probably the easiest way 
to find out!

Tim


--- In Doepfer_a100@yahoogroups.com, "Mickey Finn" <hornography@y...> 
wrote:
> So I had just recently posted that I was having trouble with my 
190. I had received it a 
> month ago but finally got around to plugging a midi cable into it.. 
I could not get any 
> gate/clock leds to light. It would select options (config/perform) 
with the correct led 
> sequence, and even list the version number; but there was something 
> wrong.. I opened her up and re checked the cables. I powered up and 
blew a fuse. I then 
> replaced the fuse and powered up again and smoke started pouring 
from the 190.. I 
> powered down and opened up the 190 and the Q1 transistor (bc549) 
had pretty much 
> melted.. the rest of the system is fine, I just checked; so the 
power supply is okay.. Maybe 
> this was a  faulty 190? I'll return it, or should I try replacing 
the Q1 transistor? Anybody 
> else have this problem??
> 
> 
> Coleman.