**FIXED** Shutter circuit fried...replacement or repair?

[DaveL59]

hmm should work but not quite a trad crowbar, you'd normally do something like this tho not simple in a pre-built circuit but can be done.

Adam if you do add a zener in for this  I'd stick a note by the fuse too, to remind you to check the zener diode before replacing so you don't end up just popping fuses should it have triggered and then get real frustrated with what's mysteriously going on 🙂 

[Skipper Billy]

On 05/10/2020 at 00:05, DaveL59 said:

talking of which, did you manage to get the mirror on your 5d sorted in the end?

I did thanks. There is a very highly rated camera repair centre in Glasgow and they quoted £60 plus VAT to repair it, clean all internals, recalibrate the autofocus system etc.

I posted it last Weds - it arrived with them Thursday, Thursday afternoon it was fixed, Friday it was posted back, yesterday it arrived back as good as new!

Highly recommended https://www.ajjohnstone.net/

 

[wulfrun]

5 minutes ago, DaveL59 said:

hmm should work but not quite a trad crowbar, you'd normally do something like this tho not simple in a pre-built circuit but can be done.

Adam if you do add a zener in for this  I'd stick a note by the fuse too, to remind you to check the zener diode before replacing so you don't end up just popping fuses should it have triggered and then get real frustrated with what's mysteriously going on 🙂 

The idea was to keep it simple, one component, whilst providing some protection against over-voltage. The probability of a 7805 going short isn't that high but for a few pence why not. Perhaps a liberty to call it a crowbar circuit but that is its function. Agreed the zener should be checked if the fuse blows without obvious cause.

[tooth_dr]

Would either of you mind drawing in on the diagram where I need to attach the ends to so I don’t inadvertently blow something. 

[wulfrun]

13 minutes ago, tooth_dr said:

Would either of you mind drawing in on the diagram where I need to attach the ends to so I don’t inadvertently blow something. 

Connect it across C3, which is next to the voltage regulator, not really in need of a diagram since it's marked on the board. Make sure than banded end of the zener connects to the positive side of C3 (work it out or use a test meter to be sure). Without having the board in front of me, I'm not quite sure but possibly solder it to the underside of the board onto the pads for C3? Whichever way you do it, use sleeving on the leads, insulated wires or whatever it takes to ensure you don't make inadvertent connections elsewhere. Also, double check everything before powering up again.

[DaveL59]

23 minutes ago, tooth_dr said:

Would either of you mind drawing in on the diagram where I need to attach the ends to so I don’t inadvertently blow something. 

here you go

[symmetal]

What's the value of the fuse on the board Adam?

As it's also supplying the power to the motor it's likely to be quite high like 10A or so, as the motor start up current will be high. To quickly blow a 10A fuse you need to pass far more than 10A through it. If the 7805 fails again, by the time the fuse blows, if it does at all, then along with the newly added zener, diode D3, the faulty 7805 and the PCB track connecting them will have possibly, burned away. The first component to burn to an open circuit will stop the current flow. Not necessarily the zener.

To make the scenario work without causing a lot of smoke and charred remains, another fuse of a lot lower capacity, like 0.5A, needs to be fitted in series with diode D3, which involves cutting the PCB track and adding a fuse holder fixed to a blank area of board, wired to each side of the newly cut track. This fuse would likely blow before the zener got too hot so the zener would survive too.

However, as the PIC is the only component which is difficult to replace on the board, and it seemed to survive with 12V, you could leave things as they are, just adding the heat sink as mentioned as a precaution to the regulator. The relay coils only draw 80mA and only 1 is ever switched at a time so I wouldn't have thought the regulator gets too hot. Passing say, 150mA, it dissipates 1 watt, fed from 12V, so would get quite hot eventually if the shutter was driven continuously, but that's not the norm. 🙂

Alan

Edited October 6, 2020 by symmetal
spelling

[wulfrun]

55 minutes ago, symmetal said:

What's the value of the fuse on the board Adam?

As it's also supplying the power to the motor it's likely to be quite high like 10A or so, as the motor start up current will be high. To quickly blow a 10A fuse you need to pass far more than 10A through it. If the 7805 fails again, by the time the fuse blows, if it does at all, then along with the newly added zener, diode D3, the faulty 7805 and the PCB track connecting them will have possibly, burned away. The first component to burn to an open circuit will stop the current flow. Not necessarily the zener.

To make the scenario work without causing a lot of smoke and charred remains, another fuse of a lot lower capacity, like 0.5A, needs to be fitted in series with diode D3, which involves cutting the PCB track and adding a fuse holder fixed to a blank area of board, wired to each side of the newly cut track. This fuse would likely blow before the zener got too hot so the zener would survive too.

However, as the PIC is the only component which is difficult to replace on the board, and it seemed to survive with 12V, you could leave things as they are, just adding the heat sink as mentioned as a precaution to the regulator. The relay coils only draw 80mA and only 1 is ever switched at a time so I wouldn't have thought the regulator gets too hot. Passing say, 150mA, it dissapates 1 watt, fed from 12V, so would quite get hot eventually if the shutter was driven continuously, but that's not the norm. 🙂

Alan

Fair point and well spotted, not something I'd actually noticed that the main fuse supplies everything. Indeed a fuse needs a serious overload to blow quickly, the zener could burn out its internal leads before the tracks go, if the fuse is as high as that. That would leave a weakness in the zener idea as suggested.

[symmetal]

Using the PCB calculator tools in KiCad you can work out the temperature rise for different current and track widths.

The track around the regulator is about 1.25mm (half the width of the regulator pin spacing) and passing 10A the PCB track will rise to around 200 deg C above ambient. 😬 The calculations are only valid up to 100 C though, and a current of 7.7A gives a 100 C temperature rise.

With Adam's original burnt track I think it's just the green solder resist layer which has burnt off and the track itself probably survived, though the bonding holding it to the board may have been weakened.

Alan

 

[tooth_dr]

On 06/10/2020 at 17:13, symmetal said:

Using the PCB calculator tools in KiCad you can work out the temperature rise for different current and track widths.

The track around the regulator is about 1.25mm (half the width of the regulator pin spacing) and passing 10A the PCB track will rise to around 200 deg C above ambient. 😬 The calculations are only valid up to 100 C though, and a current of 7.7A gives a 100 C temperature rise.

With Adam's original burnt track I think it's just the green solder resist layer which has burnt off and the track itself probably survived, though the bonding holding it to the board may have been weakened.

Alan

 

It was a very brief amount of time because I was only holding the wires on to the motor and as soon as I saw something happening I let go (still too late though)

I'll check that fuse now and reply.

[tooth_dr]

The shutter drive was being temperamental recently. I checked the wiring and the solder joints etc. I found it would go down but not up, then other times it would work ok, and sometimes with a delay of 2 seconds.

Well tonight it went pop, and a small capacitor has exploded!

Do you reckon there will be more harm done?  I’ve ordered a replacement cap, just to try and resurrect it.

 

[symmetal]

15 hours ago, tooth_dr said:

Do you reckon there will be more harm done?  I’ve ordered a replacement cap, just to try and resurrect it.

I wouldn't think it caused any other harm. It's only there to help smooth the DC input to the regulator from any sudden changes on the 12V input due to the large current spikes when the motor turns on and off.

I also notice there is no protection from the motor back emf visible in the circuit particularly from when the motor turns off. There may be an RC snubber (resistor and capacitor in series) across the motor terminals to reduce its effects. You can't put a diode across the motor terminals as the polarity changes when you change direction. You can put a reverse biased diode in the 12V going to the regulator, for example across the capacitor which has blown. It doesn't need to be a high power diode, a standard 1A rectifier diode will do.

Also check the working voltage of the blown capacitor. It's safer to make this at least 25V and preferably 50V. It looks like a voltage spike may have caused the capacitor to break down and start to draw current leading to it overheating and blowing.

Alan

[tooth_dr]

7 hours ago, symmetal said:

I wouldn't think it caused any other harm. It's only there to help smooth the DC input to the regulator from any sudden changes on the 12V input due to the large current spikes when the motor turns on and off.

I also notice there is no protection from the motor back emf visible in the circuit particularly from when the motor turns off. There may be an RC snubber (resistor and capacitor in series) across the motor terminals to reduce its effects. You can't put a diode across the motor terminals as the polarity changes when you change direction. You can put a reverse biased diode in the 12V going to the regulator, for example across the capacitor which has blown. It doesn't need to be a high power diode, a standard 1A rectifier diode will do.

Also check the working voltage of the blown capacitor. It's safer to make this at least 25V and preferably 50V. It looks like a voltage spike may have caused the capacitor to break down and start to draw current leading to it overheating and blowing.

Alan

Thanks Alan.  I replaced the capacitor and it still wasnt working, so I checked the 7805 voltage regulator and it was letting 12v through again (did the same thing previously).  I have changed it and it is sort of working again.  It stops half way up, and I have to start it again with the rocker switch.  It goes down ok so must be something to do with the load on the system when pulling shutter up.  I'll lubricate the runners for the shutter to ease the pressure but would you have any idea what might be happening here?  I suppose I'm grateful it's working again  but dont like temperamental things.

[symmetal]

The 7805 doesn't look like it's heat stressed so I can only suggest voltage spikes from the motor are causing the failures. The 7805 failing on its own wouldn't have taken out the electrolytic. The 7805 should work up to 35V DC input. It's possible the suppression snubber on the motor itself has failed or become disconnected. If may be worth opening up the motor to have a look, if it's possible.

Alternatively, to suppress voltage spikes, as well as the diode I mentioned, I suggest putting a LC filter in the 12V to the regulator like this. Ignore the horizontal line across the middle, I didn't move the mouse cursor off the diagram before grabbing it. 🤭

D2 should suppress any negative spikes being caused by the motor turning off. D1 should help anyway, but D2 will shunt it to ground. With C1 as 100uF the LC circuit starts suppressing AC voltage frequencies above 1000Hz. Using 1000uF it will start suppression above 250Hz. The danger in the voltage spikes will be the higher frequencies probably around 5kHz or more so the spike will be reduced to a gentle bump of maybe a volt or so at most rather than the 10s of volts which seem to be happening. I put 25V on the diagram, but a 35V or even 50V electroltic would be preferred.

Here's a link to the inductor. Of course any inductor around this value capable of passing at least 1A will be fine. I normally use radial lead components but an axial one as shown may be better for you and this one looked suitable.

Here's a link to a suitable ceramic capacitor. The circuit will work fine without it but it's an extra belt and braces. Ceramic capacitors are good at shunting high frequencies. Electrolytics have a built in self inductance, so are not so effective at high frequencies unless you pay more for special ones. If you use it put the ceramic as close to the regulator as you can. 

I tend to use Farnell or RS, but of course you can get components cheaper from other places if you wish.

You could drill some holes in your PCB to mount the extra components if you have a dremel type drill with fine bits of 1mm or so. 🙂

As another thought, if you didn't want to add the extra components, you could disconnect the wire of D1 that's going to the PCB fuse and wire that disconnected end directly back to the battery with another wire and smaller fuse. The battery is actually a huge capacitor and any spikes on the motor 12V go back to the battery and then just the residual spike after the battery has suppressed it goes to your regulator. The possible drawback is that the ground on the board is also carrying voltage spikes so a separate ground path to the battery is also needed. This is not so easy to achieve as the ground is more interconnected on the board and is not so easy to isolate the motor ground from the electronics ground.

Anyway, some food for thought Adam. 🙂

Alan 

Edited October 19, 2021 by symmetal

[tooth_dr]

8 hours ago, symmetal said:

The 7805 doesn't look like it's heat stressed so I can only suggest voltage spikes from the motor are causing the failures. The 7805 failing on its own wouldn't have taken out the electrolytic. The 7805 should work up to 35V DC input. It's possible the suppression snubber on the motor itself has failed or become disconnected. If may be worth opening up the motor to have a look, if it's possible.

Alternatively, to suppress voltage spikes, as well as the diode I mentioned, I suggest putting a LC filter in the 12V to the regulator like this. Ignore the horizontal line across the middle, I didn't move the mouse cursor off the diagram before grabbing it. 🤭

D2 should suppress any negative spikes being caused by the motor turning off. D1 should help anyway, but D2 will shunt it to ground. With C1 as 100uF the LC circuit starts suppressing AC voltage frequencies above 1000Hz. Using 1000uF it will start suppression above 250Hz. The danger in the voltage spikes will be the higher frequencies probably around 5kHz or more so the spike will be reduced to a gentle bump of maybe a volt or so at most rather than the 10s of volts which seem to be happening. I put 25V on the diagram, but a 35V or even 50V electroltic would be preferred.

Here's a link to the inductor. Of course any inductor around this value capable of passing at least 1A will be fine. I normally use radial lead components but an axial one as shown may be better for you and this one looked suitable.

Here's a link to a suitable ceramic capacitor. The circuit will work fine without it but it's an extra belt and braces. Ceramic capacitors are good at shunting high frequencies. Electrolytics have a built in self inductance, so are not so effective at high frequencies unless you pay more for special ones. If you use it put the ceramic as close to the regulator as you can. 

I tend to use Farnell or RS, but of course you can get components cheaper from other places if you wish.

You could drill some holes in your PCB to mount the extra components if you have a dremel type drill with fine bits of 1mm or so. 🙂

As another thought, if you didn't want to add the extra components, you could disconnect the wire of D1 that's going to the PCB fuse and wire that disconnected end directly back to the battery with another wire and smaller fuse. The battery is actually a huge capacitor and any spikes on the motor 12V go back to the battery and then just the residual spike after the battery has suppressed it goes to your regulator. The possible drawback is that the ground on the board is also carrying voltage spikes so a separate ground path to the battery is also needed. This is not so easy to achieve as the ground is more interconnected on the board and is not so easy to isolate the motor ground from the electronics ground.

Anyway, some food for thought Adam. 🙂

Alan 

Hi Alan, thanks for this comprehensive answer.  I'm pretty happy using a soldering iron, but when I see the diagram and read the instructions I find it very difficult to comprehend 😔

Would it be possible to show me visually when the stuff goes and connects to?  Like if you draw on a photo of the board?  If it isnt possible no problem!  

[tooth_dr]

Alan, sorry again for more questions.  I have also noticed something inconsistent (not a new problem as it's always existed from when I acquired the dome) - sometimes I'll press the rocker switch for the shutter to move and there will be a delay before it starts to move, of 1-5 seconds.  However on some occasions it moves immediately on activating the switch.  If I remotely activate the shutter using the PC via the bluetooth board, I can hear a click, and again there is a delay for a few seconds before the shutter starts to move.  

[symmetal]

4 hours ago, tooth_dr said:

Hi Alan, thanks for this comprehensive answer.  I'm pretty happy using a soldering iron, but when I see the diagram and read the instructions I find it very difficult to comprehend 😔

Would it be possible to show me visually when the stuff goes and connects to?  Like if you draw on a photo of the board?  If it isnt possible no problem!  

No problem Adam. I'll look at the board layout and suggest where the components can be fitted, and get back to you.

3 hours ago, tooth_dr said:

Alan, sorry again for more questions.  I have also noticed something inconsistent (not a new problem as it's always existed from when I acquired the dome) - sometimes I'll press the rocker switch for the shutter to move and there will be a delay before it starts to move, of 1-5 seconds.  However on some occasions it moves immediately on activating the switch.  If I remotely activate the shutter using the PC via the bluetooth board, I can hear a click, and again there is a delay for a few seconds before the shutter starts to move.  

This suggests a motor problem or the wiring to the motor. The relays have been replaced so it's unlikely not them giving a poor connection on one of the contacts. It would be useful to measure the voltage on the 2 motor pins, MOT+ and MOT- on the exposed pins on the rear of connector J1. When the motor fails to move for a few seconds, see if 12V is still measured here. If it is still 12V then the motor or wiring to the motor is at fault. If it's significantly below 12V and there is still 12V measured on the BAT+ and BAT- pins on the same connector then there is a momentary high resistance path between the  battery and that point, possibly a poor solder connection on the PCB. It's worth checking that, before proceeding with any other modifications. There would often be some blackening visible around the solder joint in that case due to localized heating.

Alan

[tooth_dr]

9 minutes ago, symmetal said:

It would be useful to measure the voltage on the 2 motor pins, MOT+ and MOT- on the exposed pins on the rear of connector J1. When the motor fails to move for a few seconds, see if 12V is still measured here. If it is still 12V then the motor or wiring to the motor is at fault. If it's significantly below 12V and there is still 12V measured on the BAT+ and BAT- pins on the same connector then there is a momentary high resistance path between the  battery and that point, possibly a poor solder connection on the PCB. It's worth checking that, before proceeding with any other modifications. There would often be some blackening visible around the solder joint in that case due to localized heating.

Thanks Alan, I will check this later on.  When it was messing on Sunday, just before it blew the capacitor, it was clicking but not moving.  I measured the output at the MOT+ MOT- pins on the board after it clicked, to check if there was power going to the motor.  There was 12v at the board, but it was 0v at the motor end.  I reseated the wires on the board and resoldered the wires to the motor end, but the copper wires both + and  - had went sort of black and were hard to solder.  I cleaned it as best as I could before soldering, but maybe I should replace these wires?

[symmetal]

19 minutes ago, tooth_dr said:

Thanks Alan, I will check this later on.  When it was messing on Sunday, just before it blew the capacitor, it was clicking but not moving.  I measured the output at the MOT+ MOT- pins on the board after it clicked, to check if there was power going to the motor.  There was 12v at the board, but it was 0v at the motor end.  I reseated the wires on the board and resoldered the wires to the motor end, but the copper wires both + and  - had went sort of black and were hard to solder.  I cleaned it as best as I could before soldering, but maybe I should replace these wires?

This does suggest the wiring from the board to the motor is giving problems and is worth replacing. It may be the connector on the board is also giving a poor connection on the two motor pins so it may be worth soldering the new motor wires direct to the PCB tracks, perhaps via a 2-way in-line connector if you need to have to disconnect the board in the future.

If the motor connections are making and breaking repeatly before getting a good enough connection to move the motor, this would cause repeated current surges through the motor windings and the breaking connection in particular will give rise to a succession of voltage spikes on the motor terminals due to the sudden collapse of the magnetic field in the motor. The motor is really a big inductor. The snubber circuit, mentioned previously, across the motor terminals is there to suppress these voltage spikes by absorbing the energy from the collapsing magnetic field.

Maybe your snubber has failed, and the repeated voltage spikes are causing your 7805 regulator to eventually blow, as well as the capacitor, so you could fit another one across the two motor terminals like this , or something like this from ebay. These should significantly reduce any voltage spikes generated and probably save you having to add extra filtering in the 7805 supply. You want to install the snubber close to the motor itself not at the PCB end.

So new motor wires and a snubber is your first step. 😀

Alan

[tooth_dr]

Cheers Alan.
 

Firstly this is the motor

https://www.distrelec.de/en/dc-motor-40-mm-with-gearbox-246-12-vdc-micro-motors-e192-12-246/p/15445564

Secondly, when you say add the snubber across the motor terminals what does this mean exactly?  Sorry for being dumb, where does x and y go?

 

 

 

 

[symmetal]

Hi Adam,

X would go to one of the 2 motor terminals,  while Y would go to the other terminal. The snubber polarity isn't important, but you could connect X to motor +ve along with the +ve motor wire from your PCB, while Y would then connect to motor -ve along with the -ve motor wire from your PCB.

Alan

[tooth_dr]

2 hours ago, symmetal said:

Hi Adam,

X would go to one of the 2 motor terminals,  while Y would go to the other terminal. The snubber polarity isn't important, but you could connect X to motor +ve along with the +ve motor wire from your PCB, while Y would then connect to motor -ve along with the -ve motor wire from your PCB.

Alan

Cheers Alan, that was what I was thinking, but thanks for clarifying it.  Once I get this delivered and fitted I'll update the thread.