Help with Pulsar Dimmer repair

[Peter18]

I am trying to help a village Am Dram group keep their collection of analogue 6 X 10A Pulsar dimmers working. They have proved remarkably reliable until a few days ago when three of the six channels on one of the dimmers failed to respond to the analogue desk. The channels affected are 4,5 & 6 and despite no response from the relevent channel faders, sockets 4,5 & 6 do still have the expected low output when the pre-heat is switched on Swapping dimmers around appears to rule out a desk or cable issue.

Does this fault ring any bells with those with long memories? Does anyone have a schematic for these early dimmers?. I appreciate that these units are pretty straightforward and it should be possible to fault find easily with the unit on the bench. However I am about 100 miles away from the dimmer at the moment and would like to be able to fix it without having to take it back to the workshop, so being up to speed when I first take the back off 'on site' would be an advantage and could ensure I have the correct spares to hand.

Any help would be much appreciated.

[DrV]

Haven't got a schematic but from a couple of photos of the PCB it appears to use both H11A1 and IS608 optos. The first is a transistor output type and the second is an opto triac. Can't see how many of each type (which would give a clue to where they are in the circuit) but I wouldn't be surprised if the IS608 is one per channel and the H11A1 is one per phase in the ramp circuit. The up side is that on my photo they are on sockets which makes on-site repair a lot easier.

 

I think the last one of these I repaired had broken tracks around the input DIN connector and I think the way these are wired means that they are in two sets of 3. Just occurred to me - they haven't moved the DIN connectors around have they? I think it's possible to arrange this so that only half the channels work. All a bit vague I'm afraid as it's a long time since I fixed one!

Dave

[IRW]

If they're rackpacks, I'm pretty sure the schematic is printed on the top. I have some in the garage, but they're not overly accessible at the moment, although I could dig one out if no-one else has one to hand. IIRC, there's not too much that can go wrong with these, so probably worth going in armed with a reasonable soldering iron and some triacs, which, in my experience, have a habit of blowing before the fuses, especially if the wrong fuses are used! I think you'll need a smallish nut-spinner/socket set to undo the nut holding the triac down as well.

 

Ian

 

Strike that, I just pulled one of mine half out after finding this thread that I started four years ago! The diagram on the top is mains wiring information.

[DrV]

Not likely to be triacs if the pre-heat is working correctly.

[timsabre]

Just occurred to me - they haven't moved the DIN connectors around have they? I think it's possible to arrange this so that only half the channels work.

 

My money would be on this one... There's a lot of different versions of the Pulsar packs but some have a separate set of 8-pin DINS that only do 3 of the channels, for compatibility with their 3 way packs, and they're on the back so easy to get the wrong ones. If the desk is a pulsar desk, then they sometimes also have 3-channel only outputs as well as the 6-channel outputs so the mistake could be at the desk end either.

[Peter18]

To update - the cabling and sockets have been checked by the local team, and being plugged in to the wrong socket is not the problem. Also the 'Full overide' switch does NOT bring the channel up to full on 4, 5 & 6 (which presumably would confirm that it is not the cable / socket).

[Eeen]

I know a small theatre that has some pulsar dimmers they are looking to shift... in the ascot area... I think they've got some old zero88 betas too and a demux to boot. if thats close to your faulty ones you could use the 3 ( I think) they have I uninstalled them 10 years ago and they have just sat in a dimmer room getting dusty.

 

hope that might help.

[Peter18]

I know a small theatre that has some pulsar dimmers they are looking to shift... in the ascot area... I think they've got some old zero88 betas too and a demux to boot. if thats close to your faulty ones you could use the 3 ( I think) they have I uninstalled them 10 years ago and they have just sat in a dimmer room getting dusty.

 

hope that might help.

 

Many thanks for the kind offer - PM sent.

As an update, I collected the faulty dimmer yesterday and now have it in the woekshop. It does appear to be a LM324N quad opamp - two used one for channels 1-3 and one for 4-6. Unfortunately this is not socketed so replacing it will create a bit of work!

Thanks for all the suggestions.

[timsabre]

For easy replacement cut off all the pins with side cutters and remove the body of the chip. Then using tweezers or fine pliers you can heat up and pull out each pin individually, then use a solder sucker to clean the holes out.

[Peter18]

For easy replacement cut off all the pins with side cutters and remove the body of the chip. Then using tweezers or fine pliers you can heat up and pull out each pin individually, then use a solder sucker to clean the holes out.

 

Thanks for the tip!

[Quasarkeith]

For Archive purposes.

 

I have 48 x 10 amp Pulsar Rackpak with a few problems with channels not working.

Doing internet search does not throw up Schematic. Or that much knowledge of fault repair.

Pulsar are now Luxeous. Having always been a great fan of Pulsar I was greatly warmed to discover that they are willing to help with ALL their legacy products.

I have not tried out this facility as of writing. But I feel confident enough to leave this link to their site. https://pulsarlight..../pulsar-legacy/

[timsabre]

It's a completely different group of people now, there is little knowledge of the legacy products ... and I can't see any schematics or servicing info on that link, just user manuals - have you found schematics somewhere as that would probably be useful to lots of people.

[Brian]

The Rackpak design is very basic. It should take you less than 30 minutes to sketch out the schematic.

[sandall]

The Rackpak design is very basic. It should take you less than 30 minutes to sketch out the schematic.

The website implies you can ask for schematics.

[LX Tech]

If anyone still wants or needs schematics for Pulsar 4U 6 x 10A channel Rackpacks private message me your email, & I will send them across.

 

Its not fantastic quality I am afraid as the original info was in the form of a fax, but it should be more than clear enough still.