Doepfer

Greetings list,

I'm having problems with my Doepfer A155 sequencer. I use it with the 
A154. My problem is in the A155 first CV sequence row. Only two steps 
of the eight actually produce voltages. I'm not sure why this is, as 
the second CV sequence works wonderfully.

Anyone have any suggestions? I've contacted Doepfer through their 
hardware email address, but have yet to receive a response.

> I'm having problems with my Doepfer A155 sequencer. I use it with the 
> A154. My problem is in the A155 first CV sequence row. Only two steps 
> of the eight actually produce voltages. I'm not sure why this is, as 
> the second CV sequence works wonderfully.

Sounds like trouble with the ribbon cable connecting everything 
together. Each step in the sequence is 'addressed' via this cable, 
using 3 binary lines (hence 2 x 2 x 2 = 8) - as you are only getting 
two steps from the top row, it sounds as though the ribbon is only 
making connection on 1 of the 3 address lines. The ribbon goes to the 
bottom board (second row), middle board (top row), and then to the 
trigger/gate board. Since the bottom row is working, the signal appears 
to be good there, so there may be a break in the cable, or the 
connector to the top row (middle board) is bad - are the trigger/gates 
working properly (which are on the end of the ribbon)?

What you could try is to place the connector for the bottom 
board/second row onto the middle board/top row, but take care to keep 
the orientation the same - just leave the bottom board unconnected, and 
see if this makes the first row work. If so, you'll need a new ribbon, 
as it is not worth trying to fix a bad one.

Also if the ICs are in sockets, check these are seated properly, 
especially the '4051 which controls the switching.

Tim

Tim! You are the man. The portion of the cable that is plugged into 
that sequencing board was bad. Thank you for the well informed post.

> Greetings list,
>
> I'm having problems with my Doepfer A155 sequencer. I use it with the
> A154. My problem is in the A155 first CV sequence row. Only two steps
> of the eight actually produce voltages. I'm not sure why this is, as
> the second CV sequence works wonderfully.
>
> Anyone have any suggestions? I've contacted Doepfer through their
> hardware email address, but have yet to receive a response.

Yes, we had weekend :-)

It's difficult to make a diagnosis from the distance. First of all I'd take
a look at the connectors of the ribbon cables if they are firmly fixed to
the pin header on the pc boards. Maybe the upper board does not receive all
control signals (e.g. addresses) because of a loose connector. If this does
not help the module has to be repaired. Probably one of the multiplexers
(CD4051) is defective and has to be replaced. If you are a bit familiar you
could try to get an CD4051 and replace it by yourself (all integrated
circuits are equipped with sockets). Otherwise the module has to be sent in
for repair to the representative in your country.

Best wishes
Dieter Doepfer