Author Topic: PCB Where did I go wrong?  (Read 11678 times)

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Offline sleemanj

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Re: PCB Where did I go wrong?
« Reply #25 on: February 11, 2017, 07:37:39 am »
If R1 is removed then.

Remove C1

Still problem?

Remove C2

Still problem?

Remove diodes.

Still problem?


If you build up a second board, test as you go.
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Offline Cubdriver

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Re: PCB Where did I go wrong?
« Reply #26 on: February 11, 2017, 08:15:53 am »
Long shot - in an earlier post, you said transformer secondaries - are you using a transformer with multiple secondary windings that can be connected in series to double the output voltage, or in parallel to double the current capacity?  If so, and you're doing parallel for additional current capacity, are you sure that the windings are phased correctly?  If you wire them in opposition rather than in phase, they're effectively shorted, and you'll get no voltage out and a very hot transformer. 

If you have a dual secondary transformer and you're doing the parallel thing, try powering the supply with just one of the secondary windings and see what happens.

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #27 on: February 11, 2017, 08:23:00 am »
Tried another board just with diodes populated measured 14v D.C. From 24vac tap but the tranny got too hot too touch in a matter of 15-20 seconds something is seriously up!


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Offline Cubdriver

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Re: PCB Where did I go wrong?
« Reply #28 on: February 11, 2017, 08:37:51 am »
Just the diode bridge?  What diodes are you using?  Is it possible you've inadvertently used zeners in the bridge?

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #29 on: February 11, 2017, 08:46:43 am »
Just the diode bridge?  What diodes are you using?  Is it possible you've inadvertently used zeners in the bridge?

-Pat
Yeh just the ac/D.C. D1-d4 here's the ones

I used had lying around

http://au.mouser.com/Search/m_ProductDetail.aspx?r=625-SB5H100-E3
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #30 on: February 11, 2017, 08:52:29 am »
Long shot - in an earlier post, you said transformer secondaries - are you using a transformer with multiple secondary windings that can be connected in series to double the output voltage, or in parallel to double the current capacity?  If so, and you're doing parallel for additional current capacity, are you sure that the windings are phased correctly?  If you wire them in opposition rather than in phase, they're effectively shorted, and you'll get no voltage out and a very hot transformer. 

If you have a dual secondary transformer and you're doing the parallel thing, try powering the supply with just one of the secondary windings and see what happens.

-Pat
Hey Cub!

I've tried two transformers one which had 2x20vac secondary and 3x12 which was a custom made one. That one over heated.

And one which was a 115/230 and 12/24vac. I jumpered the wires together in series as per the colors it outlined in the note, it didn't mention anything else about phase so not sure only which primary and secondaries to tie to each other for parallel/series primary/secondary operations


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Offline Dubbie

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Re: PCB Where did I go wrong?
« Reply #31 on: February 11, 2017, 08:56:59 am »
Seems like the transformer wiring might be suspect. Double check what you are doing there with a meter.
 

Offline Cubdriver

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Re: PCB Where did I go wrong?
« Reply #32 on: February 11, 2017, 09:00:14 am »
Those rectifiers should be fine.  I'm stumped - with just the bridge in place there should really be no current draw.

Could you post a picture of the assembly, transformer too?

I'm afraid I'm not going to be much more help now as I need to get some sleep.  It's 4 am here.  I'll look again later today and hopefully be able to assist if someone else hasn't in the meantime...

-Pat
If it jams, force it.  If it breaks, you needed a new one anyway...
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #33 on: February 11, 2017, 09:00:19 am »
If R1 is removed then.

Remove C1

Still problem?

Remove C2

Still problem?

Remove diodes.

Still problem?


If you build up a second board, test as you go.


Yup that's what I did and with just d1-d4 on board issue straight away
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #34 on: February 11, 2017, 09:06:23 am »
Seems like the transformer wiring might be suspect. Double check what you are doing there with a meter.


Meter is fine it's only when I connect it to the board there is an issue.


If I just leave it disconnected without load (not connected to the pcb) no temp rise and reads 20vac.

As soon as I connect heats up and issues start same with both trannies
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #35 on: February 11, 2017, 09:23:24 am »
Those rectifiers should be fine.  I'm stumped - with just the bridge in place there should really be no current draw.

Could you post a picture of the assembly, transformer too?

I'm afraid I'm not going to be much more help now as I need to get some sleep.  It's 4 am here.  I'll look again later today and hopefully be able to assist if someone else hasn't in the meantime...

-Pat


Hey pat,

Thanks mate so here's a few pics.

The large mounted tranny the primary are blue Connected to Live and neutral on iec connector.
Earth I've iec is taken to ground ( it's a wooden case so it's a metal threaded insert and copper sheeting over but yes to metal contact of base) it's tied to the same place as the transfomer shield wire. Secondaries red 20vac

The other transformer, you can see the way I've jumpered the wires in series.

Here's also a pic of a populated board and also another board I just tried with just the diodes and same thing happens, although this time I did get 14vdc measurement across the output of the diodes to gnd (it was 24vac input) but tranny got very hot very quick!!!!


Got me stumped! Transformers are fine not connected to the boards as soon as I connect then issues happen it happen with both transformers as well!

 

Offline Rerouter

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Re: PCB Where did I go wrong?
« Reply #36 on: February 11, 2017, 09:28:48 am »
Only connect 1 secondary, and see what you get, like many other posters, you likely have mismatched secondaries, or have them connected antiparrellel.
 

Offline neil t

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Re: PCB Where did I go wrong?
« Reply #37 on: February 11, 2017, 09:45:00 am »
just for clarity you say that the blue wire =live and neutral,
the third photo down on left shows blue(neutral) grey and purple connected in series then brown (active/live) wired for 220/240 volts is that what i'm seeing.
 

Offline neil t

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Re: PCB Where did I go wrong?
« Reply #38 on: February 11, 2017, 09:58:34 am »
the colour coding your showing matches a toroid I have in my hand
the secondary's are orange yellow
                             black red
if you want parallel orange and black connected together and yellow and red connected together.
if you want series yellow and black together. You should confirm this with continuity. low ohms  in this case a 2 amp winding at 15v is 0.8 ohms

regards Neil
 

Offline Spuddevans

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Re: PCB Where did I go wrong?
« Reply #39 on: February 11, 2017, 10:08:55 am »
I see that you are using toroidal transformers with a cover which looks metallic. How is the transformer mounted? You have to be careful that you don't accidentally create a short-circuited turn by using a bolt that goes through the centre of the transformer and is attached to a conductive case/cover at both top and bottom of the transformer and thereby creating an effective short-circuit turn which will make your transformer unhappy.

Tim
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #40 on: February 11, 2017, 10:36:19 am »
just for clarity you say that the blue wire =live and neutral,
the third photo down on left shows blue(neutral) grey and purple connected in series then brown (active/live) wired for 220/240 volts is that what i'm seeing.


Hi Neil,

Sorry I realized my previous post might be confusing.

Some photos referred to this transformer

For this transformer I had yellow and black as secondary taps (with red and orange jumpered)

To be series 24v instead of 12


Primary brown and blue as primary wires and violet and grey tied together.

 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #41 on: February 11, 2017, 10:40:02 am »
I see that you are using toroidal transformers with a cover which looks metallic. How is the transformer mounted? You have to be careful that you don't accidentally create a short-circuited turn by using a bolt that goes through the centre of the transformer and is attached to a conductive case/cover at both top and bottom of the transformer and thereby creating an effective short-circuit turn which will make your transformer unhappy.

Tim


Hi Tim,

It's mounted on a platter which is on m4 standoffs with a bolt into the transfomer via hole in platter. Both the bolt and platter were provided to me with the tranny.

Nothing is touching on top mate been in clear air
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #42 on: February 11, 2017, 10:56:27 am »
the colour coding your showing matches a toroid I have in my hand
the secondary's are orange yellow
                             black red
if you want parallel orange and black connected together and yellow and red connected together.
if you want series yellow and black together. You should confirm this with continuity. low ohms  in this case a 2 amp winding at 15v is 0.8 ohms



Hi Neil,

Thanks for your reply. It's a triad vpt24-1040.

Here's a clearer pic of how it's wired and the data sheet.

I assumed I wired it correctly for 230v/24v secondary operation


regards Neil



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Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #43 on: February 11, 2017, 11:01:19 am »
The only other thing I've noticed on the other transformer (large mounted one) which may shed some light is, each primary and secondary has one of the two with white tape on it??

I'm not sure what that's meant to mean in relation to me hooking it up?


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Offline neil t

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Re: PCB Where did I go wrong?
« Reply #44 on: February 11, 2017, 11:21:48 am »
The only other thing I've noticed on the other transformer (large mounted one) which may shed some light is, each primary and secondary has one of the two with white tape on it??

I'm not sure what that's meant to mean in relation to me hooking it up?


Sent from my 486 IBM WIN 3.1x Desktop...
it is possible that they are phase markings, but couldn't say with any degree of certainty/safety, this would suggest that series would go something like secondary winding one no tape connected to secondary winding two taped wire, output would then be secondary winding one taped and secondary winding two no tape. again continuity testing should confirm that the individual secondary's have continuity with a smallish resistance and when connected in series that resistance should double. when all wires are disconnected no winding should have continuity with another separate winding. please take no offence these basic tests are suggested for thoroughness on my part. if the continuity tests show correct results then the next test I guess would be insulation breakdown test or a megger test which I cant help with, I have never owned or used one. needless to say safety first no shortcuts are in your best interest , fatalities happen in a heartbeat or two.

regards Neil
 

Offline Spuddevans

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Re: PCB Where did I go wrong?
« Reply #45 on: February 11, 2017, 11:33:54 am »
Have you got another transformer (a known to-be-working-ok one) that you can temporarily substitute? That should point you in the area where the fault is, if it is the transformer or the PCB.

I know it's obvious, but have you double checked each of the diodes with your meter (diode test)?

Can you wire it all up "Unmounted"? ie without the transformer mounted on the platform, without it's cover?

Can you wire a ammeter in series with one of the ac secondaries as it feeds the PCB? What does it read?

Tim
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #46 on: February 11, 2017, 11:47:21 am »
The only other thing I've noticed on the other transformer (large mounted one) which may shed some light is, each primary and secondary has one of the two with white tape on it??

I'm not sure what that's meant to mean in relation to me hooking it up?


Sent from my 486 IBM WIN 3.1x Desktop...
it is possible that they are phase markings, but couldn't say with any degree of certainty/safety, this would suggest that series would go something like secondary winding one no tape connected to secondary winding two taped wire, output would then be secondary winding one taped and secondary winding two no tape. again continuity testing should confirm that the individual secondary's have continuity with a smallish resistance and when connected in series that resistance should double. when all wires are disconnected no winding should have continuity with another separate winding. please take no offence these basic tests are suggested for thoroughness on my part. if the continuity tests show correct results then the next test I guess would be insulation breakdown test or a megger test which I cant help with, I have never owned or used one. needless to say safety first no shortcuts are in your best interest , fatalities happen in a heartbeat or two.

regards Neil


Hi Neil,

Don't take it that way at all. I'm constantly amazed and how helpful people are in this forum. Sincerely appreciate you giving advice. Whilst I'm new to electronics I know enough to ask questions when it comes to power!!!

As humbling as it is I would rather look like a newbie then fry myself!


Ok. On both trannies.

Tridad - Continuity beeps on the yellow and black 12/24 (wired for 24vac) secondary, measures 1.5ohm

Toro Transformer - 20vac 1A secondary beeps on continuity for the both of the taps, measures 1ohm
 

Offline goldfingerTopic starter

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Re: PCB Where did I go wrong?
« Reply #47 on: February 11, 2017, 11:55:58 am »
Have you got another transformer (a known to-be-working-ok one) that you can temporarily substitute? That should point you in the area where the fault is, if it is the transformer or the PCB.

I know it's obvious, but have you double checked each of the diodes with your meter (diode test)?

Can you wire it all up "Unmounted"? ie without the transformer mounted on the platform, without it's cover?

Can you wire a ammeter in series with one of the ac secondaries as it feeds the PCB? What does it read?

Tim


Hey Tim,

I've had same issue with two transformers, both work perfectly fine when not connected to the pcb, well when I say perfectly fine. They behave normally when just measuring the taps. I've also just taken out a panel mount rectifier and connected them to both transformers and measuring fine minus the voltage drop.

But as soon as I connect the transformers to the board issue they overheat straight away!

Diodes all seem fine. Forward voltage drop and then nothing other way. As above I even partially built another board with only the rectifier on it and same thing happened l!


It seems that despite some bad design around tracks on the board that no one has seen a "there is a short" so design seems to be fine just that some of my tracks are close to each other and hence cause issues.

I couldn't find a short when I tried continuity to gnd with any of the nets on a bare board

 

Offline neil t

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Re: PCB Where did I go wrong?
« Reply #48 on: February 11, 2017, 12:04:03 pm »
Hi All,

It's only my 2nd design for a PCB so be kind :) did a proto pcb of the attached board and unfortunately it didn't work.

When I hooked up the transformer got hot (as did the secondary wires) so I am assuming its some sort of short somewhere but can't work out what I've done.

I'm not sure where I have gone wrong so any feedback would be appreciated. I'm sure it's something simple but I can't seem to see where!  |O

The attached is a two layer (was meant to be a regulated power supply using an 1085) The 1085 is attached to the board via two screws and heat sink. The screw holes on  no net and have a decent keep out around the screw holes from the pour.

The top layer is for power signal and the bottom is a ground plane. No power signal is routed in the bottom layer only ground connections. The traces are 1.6mm I was planning to run a max of around 1A through the board, but realistically it wouldn't see more than a few hundred ma. R5 is to fine tune the output voltage.


If anyone has any ideas what could be wrong I would appreciate the feedback, I suspect I've done something simple and stupid, but well I can't seem to find where.

Thanks heaps guys really appreciate any feedback great bunch of members here who have always been helpful. Thanks all
Looking at picture 2 the orange tracks grey plane are they track remnants that can be seen near some diode  solder  pads if so imagine if the holes themselves not the pads are about 1mm or 39 thou then the spacing between solder pad and remnant track must be quite small it wouldn't take much for solder to creep from pad to track remnant.

regards Neil
 

Offline sleemanj

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Re: PCB Where did I go wrong?
« Reply #49 on: February 11, 2017, 12:26:52 pm »
1. On the pcb with diodes only (and without the transformer connected), confirm that there is no continuity between ac1 and ac2
2. take a picture showing exactly how you have the transformer wired to the pcb with diodes only
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