Think I Just Blew My HEQ5 Mount

[russellhq]

I plugged a new power supply into my mount (HEQ5) after checking the polarity was correct (it was) but after 3 or so seconds something went "puff" and the light went out

Double checking the power supply, it was 13.5V 5amp but I think it was AC not DC

Has anyone had any success repairing a blown mount?

[nightfisher]

hate to say it, could be a new board, not what you would like to hear

[russellhq]

New board on order... expensive lesson

[StuartJPP]

You released the magic smoke! Unfortunately we all seem to have these lessons every now and then.

Has anybody tried repairing these boards before? I am sure this isn't the first time I have heard of this.

[kirkster501]

New board on order... expensive lesson

Yep, we all have them. Like "Steve's plumbing" where water leaked all over the CH boiler control circuit board. £240 lesson.

[mareprah]

But AC hasn't got any polarity...? How did you check it then? I'm not too good of a english speaker, but I'll try to say this the way anyone could understand :

DC: current goes in one way (from - to + if I'm correct)

AC: current alternates (50Hz in most cases)...

Knowing this tells you that AC doesn't have - or + or with other words, it doesnt have polarity...

Sorry to hear your motherboard got blown, but let me just give you a tip, so you don't have to get rid of your power suply. You can make it DC with maybe a 1€ expense. You will need 4 diods (not LED's but electronic elements that don't shine, they just pass trough the current in one way, but not in the other...) and 1 conductor (hopefully I translated this correctly). The schematic looks like this:

https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/RC_Filter.png/400px-RC_Filter.png

(on this schematic there is a resistor too, but I didn't use one...)

Works for me with a 12V 8A power suply, BUT I DON'T USE IT FOR MY MOUNT!!! Not that it wouldn't work (I think 12V would be enough, should check) but I've got another one for my mount, I just use this one for other things...

CS, M

[astrosathya]

OK, Dont worry too much. New boars are available for £100 i guess. Secondly you are supposed to use a Switch Mode, Regulated 12VDC Power supply if using from the mains. I know these things look like Laptop chargers, but that doesn't mean any thing works. When it comes to expensive equipment, please make double sure you are doing the right thing. By making sure I mean not think that its the right thing ((like all of us Men so) but to read up and ask around if unsure of something.

[russellhq]

But AC hasn't got any polarity...? How did you check it then? I'm not too good of a english speaker, but I'll try to say this the way anyone could understand :

DC: current goes in one way (from - to + if I'm correct)

AC: current alternates (50Hz in most cases)...

Knowing this tells you that AC doesn't have - or + or with other words, it doesnt have polarity...

Using a 9V battery and computer fan, I connected the red wire of the fan to the +ve terminal on the battery and the black wire to the -ve side and noted the direction of spin. Reversing polarity, reversed the direction of spin. I then attached the lead from the power supply to the fan by attaching the red wire to the tip and black wire to the outside. Doing this, the fan spun in the same direction and I then assumed my supply was tip +ve. Just bad luck the fan spun in the same direction.

[russellhq]

OK, Dont worry too much. New boars are available for £100 i guess. Secondly you are supposed to use a Switch Mode, Regulated 12VDC Power supply if using from the mains. I know these things look like Laptop chargers, but that doesn't mean any thing works. When it comes to expensive equipment, please make double sure you are doing the right thing. By making sure I mean not think that its the right thing ((like all of us Men so) but to read up and ask around if unsure of something.

Is switch mode preferred to a transformer with a rectifier?

[rfdesigner]

For anyone else who's worried about experiencing the same and builds/modifies their own kit:

I've developed a lot of boards and systems for work over the years.

On most of my development boards I put a zenner diode across my supply input. In the event that the power supply gives too much the zenner will cap the supply, and will forward conduct for a reversed supply, the zenner may let out the 'magic smoke' but the PCB is saved needing only a new zenner. I've saved a number of boards this way.

If installing in a final product (or for home use) then a low resistance PTC thermistor or even a resister between the PSU and the zenner can limit currents.

I like this system as it is very simple cheap and reliable, yet gives a degree of protection, which is all that is normally needed.

Derek

[russellhq]

That sounds very interesting Derek but I have no idea how to apply it!

If I start on one side with the +ve and -ve terminals of my power supply and on the other side I have the +ve and -ve terminals of my mount, how would I wire up the bits in the middle to achieve this level of protection?

[mareprah]

If I'm correct (derek correct me please if I'm wrong) you put a diode on both of the wires. On the diode you have a white marking on one side (the diode is black), this is the "stopper". So the current can't flow from the white marking on the other side, but in reverse direction it does. You than put one diode on the negative cable of your equipment with the white marking facing your equipment and not your power suply. On the positive cable of your equipment you reverse the diode, so that the white marking is at the power suply's side and the black part is on the side of your equipment.

That trick with the fan is good, but not good enough. Believe me, the AC current was not good for it, since it has a brushless motor inside, but it wasn't to damaging for it to blow it... Sadly that was not the case for your mount. Next time, ALWAYS use a multimeter or a voltmeter...

Another trick is with a LED ... you can determine which wire is + and which is -, plus you can find out if its AC or DC (with AC the LED flickers a bit, though hard to see, it is visible, where on DC it lits without any flickering). Still, this trick is good for unexpensive stuff, but not for stuff that is 20€ or more...

[mareprah]

Something like this, but please wait for Derek to confirm my theory and the polarity of the diodes:

[rfdesigner]

A zenner diode conducts as a normal diode when 'forward biased' and again when biased beyond the zenner voltage. If you have a 12V power input then I might want to look at say a 14V zenner.. if the mount is thirsty then I'd want a fairly chunky diode..(the watts rating of the diode is how much it's designed to work at continuously, we are prepared to go well over this as we are happy to sacrifice the diode for the sake of the mount.

Something like this might be suitable:

http://uk.farnell.com/multicomp/1n5351b/diode-zener-5w-14v-5-do-201ae/dp/1798004

This will provide an Amp of clamping at 14V and more than that against you reverse biasing the mount.

The Diode should go at the mount end.. ideally permanently connected, allowing you to plug the wires in without touching the diode.

The 'bar' of the diode should go to the positive terminal. Under normal operating conditions the diode will not take any noticable current.

Derek

[rfdesigner]

Something like this, but please wait for Derek to confirm my theory and the polarity of the diodes:

no..

You don't need both, one will do.

This will do a similar thing to a zenner.. but it won't protect against over voltage and it drops volts in normal working mode

[StuartJPP]

On most of my development boards I put a zenner diode across my supply input. In the event that the power supply gives too much the zenner will cap the supply, and will forward conduct for a reversed supply, the zenner may let out the 'magic smoke' but the PCB is saved needing only a new zenner. I've saved a number of boards this way.

If installing in a final product (or for home use) then a low resistance PTC thermistor or even a resister between the PSU and the zenner can limit currents.

Derek

The 2nd approach is good, but in the first one, when the zener "lets out the magic smoke", it will likely go open circuit and you are back where you started, i.e. no protection unless it is a very large wattage zener where the smoke doesn't come out. Something needs to be inline with the supply, either a fuse or preferably a PTC/polyswitch or a large wattage low resistance resistor to dissipate the heat. The problem with polyswitches is that once tripped they never quite return to their low initial resistance.

I know that zener diodes can fail short circuit, but if the power supply is powerful enough it can burn it out and again you are back at square one.

It really does irk me that manufacturers don't spend an extra 50p to protect their circuits.

Years ago I worked for a company that made immobilisers for cars (before they were standard factory fit). Although the car battery is only 12V the board had to repeatedly survive a 200V load dump in case the alternator lead came loose. Solution was a 1 watt series resistor with a zener/transorb after the resistor and across the supply, total cost, less than 5p.

[rfdesigner]

You are correct.. the zenner can in time fail open circuit. When I've used them for board protection, so long as they are big enough then they fail on a human timescale 10s of seconds at high current, certainly long enough to notice soemthings wrong and turn it off, the zenner I picked can handle and amp or more continuously and over 6A briefly without damage, under the normal reverse bias use.. when forward biased they handle tons more.

A resetable fuse for a 1A application (2A trip) is here

http://uk.farnell.com/bourns/mf-rx110-72-0/multifuse-radial-1-1a/dp/9350128

Derek