alphapack stuck at full - not triac

[gnomatron]

I have a zero 88 alphapack 1 with a channel stuck on at full. I replaced the triac but that didn't solve it. What else should I try? I guess the fader? anything else? It also had a knackered fuse holder on the same channel, is that likely to point to anything being badly wrong?

 

(and yes, I did search the archives before posting! Couldn't find anything that helped much.)

 

I'm pretty sure it's the fader now, but a bit stuck beyond that. Seems a right pain to get into to replace. Should I even bother? a 2 channel alphapack is still moderately useful. Would analog control override the fader?

[richardash1981]

I have a zero 88 alphapack 1 with a channel stuck on at full. I replaced the triac but that didn't solve it. What else should I try? I guess the fader? anything else? It also had a knackered fuse holder on the same channel, is that likely to point to anything being badly wrong?

The damaged fuseholder suggests that the previous fuse blew slowly, getting the holder hot, which probably means the channel was overloaded (rather than a fault, short-circuit, which blows the fuse quickly). Other than increasing the likelihood of failing the triac, not sure where that gets you.

Are the triacs on the main board in the alphapack, or on separate PCBs like a betapack? With the latter, you can unplug the wiring loom (in pairs) to prove that the triac is working by having the output go off, as well as crossing with a good channel for debugging. Same trick works on Strand Act 6.

 

I'm pretty sure it's the fader now, but a bit stuck beyond that. Seems a right pain to get into to replace. Should I even bother? a 2 channel alphapack is still moderately useful. Would analog control override the fader?

Unfortunately, analogue control will be highest takes precedence (HTP), so the fader at max (if it is) will hold the channel on over the control input. Stuck at zero would be fine though, so the fader could just come out and not be replaced (or snip the legs and leave it physically in situ?). If the fader isn't physically damaged (bumps as it moves or bent/broken) and the channel hard on not flickering I would be a bit surprised if the fader itself is the cause. Could be a dry joint at the ground end of the fader though (don't know if that is hard or easy to access).

[gnomatron]

Detaching the wiring loom to the control board puts the channel at 0... I wonder if it's likely to be anything else on the control end? I made the mistake of disconnecting only one side of the triac, which ended with a knackered triac, unfortunately. There's nothing obviously physically wrong with the fader, anyway.

[Don Allen]

If the bottom end (0V)is open circuit due to a dry joint, the fader will go to maximum volts. Have a look for a dry joint on the fader or it could be a damaged track on the fader. A voltmeter will also tell you what is happening.

[vinntec]

I may be wrong, but I seem to remember that the Mk 1 AlphaPacks have a switch on the bottom which can switch the dimmers to local control only (or vice-versa, not sure) which used to cause us trouble as houselights/working lights are controlled by one - until our chief tech bypassed it. I think it was next to the power cable on the base and clicked in and out?

 

Looking up the technical docs has two possibly relevant items:

 

 

The DMX receiver firmware has a built-in test mode. To activate this, the internal ‘TEST MODE’ button mustbe held down at power-on. Normal DMX reception is disabled in this mode, and the LED blinks to indicatethis. The DMX address selection switch now selects from the functions defined in Table 3:Table 3: DMX test modes0 all off, 1 ch.1 on, 2 ch.2 on, 3 ch.3 on, 4 all ramp up, 5 all ramp down, 6 all ramp up/down, 7 chase channels 1-3, 8 ripple channels, 1-3,9 all on.

 

Also: If all outputs are stuck on, open the unit and check the operating frequency link setting, as described insection 3 above. Check and adjust the ramp calibration, as described in section 4 above. If only one output isstuck on, the most likely fault is the triac or opto-triac. Diagnosis and repair should only be conducted byexperienced service personnel familiar with triac circuits.(Section 3 says The unit’s operating mains frequency can be set to either 50Hz or 60Hz, with a link setting on the controlPCB. The link positions are indicated on the PCB itself. Note that on Alphapack 1, the control PCB will needto be removed to gain access to this link. The factory default setting is 50Hz.)

 

[ianknight]

I may be wrong, but I seem to remember that the Mk 1 AlphaPacks have a switch on the bottom which can switch the dimmers to local control only (or vice-versa, not sure) which used to cause us trouble as houselights/working lights are controlled by one - until our chief tech bypassed it. I think it was next to the power cable on the base and clicked in and out?

 

Looking up the technical docs has two possibly relevant items:

 

 

The DMX receiver firmware has a built-in test mode. To activate this, the internal ‘TEST MODE’ button mustbe held down at power-on. Normal DMX reception is disabled in this mode, and the LED blinks to indicatethis. The DMX address selection switch now selects from the functions defined in Table 3:Table 3: DMX test modes0 all off, 1 ch.1 on, 2 ch.2 on, 3 ch.3 on, 4 all ramp up, 5 all ramp down, 6 all ramp up/down, 7 chase channels 1-3, 8 ripple channels, 1-3,9 all on.

 

 

Alphapack Mk 1's don't have DMX onboard sadly and the switch changes which of 6 channels the unit responds to when connected to an external controller.

 

The original fault sounds like a fader issue - I have known them to fail and it's a relatively easy job to swap one out, so I'd start there first before overthinking what the issue might be.

[gnomatron]

Ian's dead right, no DMX on the alphapack 1, and the switch is just for channel 1-3 or 4-6 control. I'm fairly sure it's the fader or the fader board, it looks like it's had some iffy repairs before. The tracks on the pcb look a bit shot by that fader so I'm not convinced replacing it is worth the hassle. Actually the fader itself - or rather the metal bit the plastic cover goes on - is bent so that's probably it.

[Guest]

Another thing to try would be to spray some contact/switch cleaner in the fader and run the fader up and down. In the past I found a fader on my Zero88 level 12 console that didn't work at all (as opposed to being stuck at full) and with a healthy dose of contact cleaner it was back up and running. From the sounds of it if this doesn't work it may be the fader itself, so it could be worth unsoldering one of the working faders and soldering it into channel one and see whether that works.

 

Edward

[Andrew C]

Fuse holder ; change 'em all. I've done a LOT of changing holders on these. They are good for 10A, but not forever. ISTR that RS sell a 15 or 20A rated version that fit the existing holes, but it was a while ago.

[gnomatron]

The fuse holders are good, except one which I already replaced. Duff fuse holder would have the opposite effect of what I'm seeing... I can't imagine changing it for a 15A or 20A holder would be a good idea, but I suppose if the fuse inside is right it doesn't matter... given the fuse you're meant to use is a 6.3A I don't see why there'd be any bother with a 10A holder? They seem to fail mechanically, due as much as anything to the crappy plastic screwdriver slot for getting them out, rather than for electrical reasons.

[PaulDF]

It is maybe worth giving zero 88 technical a call, I have schematics for betapacks but none for alphapacks.

I imagine there will be some sort of opto coupler chip which interfaces the mains side to the electronics which, if there was a fault on the mains side could have also been taken out and gone short circuit.