Demux 48 has strange problems

[hupcey]

We have been using this Demux 48 for years in a community theater whose stage is in a local middle school. It has probably been powered up since we purchased it new back in 1994. It has worked reliably until the past show. During tech rehearsal we noticed that some dimmers were stuck on, even when we sent a total blackout to the Demux unit.

 

We measured the DC voltages of each of the outputs: most were at or near 0v, but a block was stuck at 16.4v - channels 16 through 24, plus channels 5, 8, 13. And channels 29, 32, 37, 40, 45, 48 were stuck at 5.3v.

 

 

Can you please explain what's happening here?

 

 

I measured across the battery, as suggested earlier in this forum. 3.7v with power off, 4.8v with power on.

I measured the test points: 0V = 0v, +11V = 11.2v, +V = 23v, -V = -25.2v.

The left bank (next to the logic) of LM324s Vcc = 6.8v, the right bank Vcc = 23.1v.

 

I got the data sheets for the LM324 and CD4051, hoping I could scope these and figure out what was failing. But without a circuit diagram, I'm kind of lost. I need at least some idea what is supposed to be happening.

 

The other strange thing is that when I power the unit up WITHOUT a DMX source plugged in, the three "Start Channel" digits are constantly changing. After a while it may settle down enough for you to read the "001", but still blinking "555" (maybe)?? When I hook up a valid DMX source, the "001" is steady on along with the data LED. Maybe this is normal! But this is the state the Demux lives in when not in use since the PC generating the DMX signals is powered off.

 

 

Thanks for you help.

Cheers,

John

[KWR88]

Hi John,

 

Think we have been dealing with this off forum.

Think we narrowed it down to the internal battery causing a problem.

If not please e-mail on the address below.

[hupcey]

I sent you an e-mail about this last June 22, 2008, but never received a reply.

 

I spent many, many more hours on this, and I never got consistent symptoms from day to day, even after putting in a new battery.

 

I gave up since I ran out of time (the next show was in July). Bought two used "ETC Response 32 out" DMX to analog units from PRG and installed them in the theater.

 

- John