Pulsar datapak

[KevinE]

if you managed to get 35V across the whole winding and now you only get 17.5V across one leg to the centre tap, then it suggests you've damaged something while taking it out. Check the tracks are all ok and if it's thru-hole plating, check that's intact too.

 

You say there's evidence of smoke fluid residue, so I'd be checking very carefully for any rotted tracks on the pcb. The results of smoke fluid damage can be confusing, random and difficult to trace logically. Smoke fluid is conductive into the bargain. Pay attention to around the lower edge if it's been mounted on a wall, in case that's where the fluid has gathered.

[Discostu73]

I have again re tested the voltage and all appears ok. Maybe I am a little keen to find the fault! There is definitely some residue in there, quite a bit in some places. Does this dissolve with isopropyl alcohol? Will any components be damaged if I give it a really good clean with an aerosol or two?

Because I am getting some output matching the analogue input for a while I have been assuming that the problem may not be that major. Now I am beginning to chase my tail I am wondering whether the issue is more terminal?

[KevinE]

IPA wont easily flush smoke fluid away. It all looks nice and clean but when the IPA evaporates the smoke fluid remains.

 

My experience of smoke fluid on pcbs is mainly cd players and dj mixers; and If I get a board in with smoke fluid in any amount, I put it in the sink with warm water and fairy liquid, cleaning it with a soft paint brush. Then it goes in the boiler room for 24hrs.

 

If a board has a mains transformer or relays on it, they're best removed first so they dont wick-up water; it may not come out and any residual water would have insulation and safety implications.

 

The other way if you dont fancy washing it is to take plenty of tissue paper and lay it on the board, using a stiff brush to stipple down onto the pcb to soak up as much of the stuff as possible. Then, using a mgnifier if necessary, examine the tracks for the slightest discolouration beneath the solder resist which might betray rotten copper.

[Discostu73]

Thanks for the advice. The unit has a lot of triacs and chokes which are attached to the casing off PCB, so dunking in a sink is out of the question due to physical size. If I put this in the bath I am sure instant divorce will follow! Perhaps a plant sprayer filled with nice hot soapy water and a paint brush will suffice? There are a few relays and dip switch arrays which may hold water if I am not careful, the overide dip switches is one area I will pay close attention to for obvious reasons. The fault still suggests to me that it is an input issue so I will pay close attention to the control areas. I will post again when I have tried this. Thanks again.

[richardash1981]

Back with the transformer, I have come across a fault (in a loop amplifier) which would be consistent with your symptoms: Are you confident that the centre tap of the transformer is connected to the rest of the circuit (normally the ground rail)? In the case I had, it wasn't (due to a faulty crimp header), and so the circuit ground wandered around between the positive and negative power supply rails, depending on how well balanced the loads were. In practice it started off near the middle, then drifted off one way and stuck there (at which point nothing worked) until one of the filter capacitors failed (because it was seeing twice the voltage it should have been).

Just a thought given as we have a +/- supply rails set up here which starts OK and then goes off. First thing would be to check both + and - rails to ground separately, at start-up and when the outputs have stuck.

 

[bruce]

Getting off topic, sorry, but we had a serious fire at work a few years ago. A specialist contractor was brought in to treat all of the electronic equipment - lots of computers, monitors, some A/V kit and some very expensive scientific equipment.

 

The equipment had suffered water and smoke damage. While “smoke damage” may not sound much, it’s a bit like something being painted with tar.

 

Their production line was quite impressive.

 

1. remove hard disks, and transformers if possible. Disassemble, removing PCBs from chassis.

 

2. Wash in large sinks full of hot water with detergent

 

3. Rinse with hot water

 

4. Rinse with de-ionised water

 

5. Allow to drain

 

6. (the key bit) Heat PCB in a vacuum oven for a couple of hours

 

7. Re-assemble and test.

 

Most of it survived!

[Discostu73]

So here’s a little update. Thanks to Kevin for the cleaning advice. I used a plant sprayer with good hot soapy water in it. Using a soft paint brush I gave it al a really good clean. It now shines and is clean enough to eat my dinner off! I allowed it to dry thoroughly before trying it out, but alas the fault is still just as it always has been. As I am running out of ideas I noticed another unit up for sale which I have now purchased for less money than some domestic wall plate dimmers! I am waiting for this to be delivered and holding my breath that this one works. If all goes well then I hope having a working unit as reference will help to fix the original one. If not then I am not too much out of pocket and have a box full of spares, if I can fix the original then I will have more dimming channels in my little garage than I know what to do with! Once again I will post when I have any updates.