PCB Where did I go wrong? - Page 1
Forum section: electronics / beginners

author: goldfinger
author_rank: Regular Contributor
timestamp: February 10, 2017, 10:45:34 pm
content: Hi All,It's only my 2nd design for a PCB so be kinddid 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!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

author: eugenenine
author_rank: Frequent Contributor
timestamp: February 10, 2017, 10:50:58 pm
content: What is C1?

author: goldfinger
author_rank: Regular Contributor
timestamp: February 10, 2017, 11:33:29 pm
content: Quote from: eugenenine on February 10, 2017, 10:50:58 pmHey EugenenineIt's meant to be small snubber mate

author: Unknown
author_rank: Unknown
timestamp: February 10, 2017, 11:51:27 pm
content: How's the temperature on D1-4? R1? U1?That'll give you a clue as to where the fault is...

author: Ammar
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:01:01 am
content: What is the value of C1? Also, what is the AC voltage supplied at the inputs?

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:03:55 am
content: Quote from: Ammar on February 11, 2017, 12:01:01 amHey Ammar20vac, c1 is 0.1uf rated 100vSent from my 486 IBM WIN 3.1x Desktop...

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:10:58 am
content: Quote from: Tac Eht Xilef on February 10, 2017, 11:51:27 pmHi tac,I'll have to check as when I noticed that there is no D.C. Output at all and the transfomer is getting hot (inc secondaries) I've turned off straight awayNo connected the transformer is fine measuring and no heat at all.As soon as I connect it heats up, with no D.C. On output.Diodes are over spec for circuit, elec caps are rated 63v 4700uf each.Wirewound resistor is 5w 1ohm and has around 4mm clearance under itI doubt (although could be wrong ) that it's soldering etc as I've checked board and cleaned it and doesn't seem to be any residues or spill over to gnd plane. I've placed pretty big through hole to plane spaces as you could probably seee.That's why I'm assuming I've done something Silly with board and shorted something, highly probable as new to electronics and even less experience with pcb design (which probably shows)

author: digsys
author_rank: Unknown
timestamp: February 11, 2017, 12:18:08 am
content: Well, the circuit is fine and straight-forward. Time to disconnect the Regulator and use diode test on your DMM. Also reistance checks to GND.Regulator incorrectly wired / faulty?

author: sleemanj
author_rank: Super Contributor
timestamp: February 11, 2017, 12:29:18 am
content: Traces on C1 from AC1/2 are very (needlessly) close together, check for (manufacturing defect) short (also, check for short of C1).Net C6_1 runs very (needlessly) close to ground on DC1, again check for short there.In fact you have quite a few needlessly close clearances between nets and pads not on those nets, check them all.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:38:31 am
content: Quote from: digsys on February 11, 2017, 12:18:08 amHi mate,Thanks the 1085 is already soldered to board and bent back and screwed to board.Any advice on measurements I should take would be great, fairly new so any further info on measurements I should take would be awesomeThanks heaps!

author: sleemanj
author_rank: Super Contributor
timestamp: February 11, 2017, 12:40:49 am
content: Quote from: goldfinger on February 11, 2017, 12:38:31 amNote that the tab is output positive. Make sure you have not shorted it to your ground plane via a screw.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:44:02 am
content: Quote from: sleemanj on February 11, 2017, 12:40:49 amHey sleeman thanks bud, when you say tab are you referring to the regulator package, e.g.back area that is connected to heatsink/board?Sent from my 486 IBM WIN 3.1x Desktop...

author: sleemanj
author_rank: Super Contributor
timestamp: February 11, 2017, 12:46:11 am
content: Quote from: goldfinger on February 11, 2017, 12:44:02 amYes that is the tab.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:46:50 am
content: Quote from: sleemanj on February 11, 2017, 12:46:11 amOk thanks heaps, sorry thought so just wanted to check

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 01:14:51 am
content: Thanks for everyone's feedback thus far appreciated allSent from my 486 IBM WIN 3.1x Desktop...

author: Cubdriver
author_rank: Unknown
timestamp: February 11, 2017, 01:44:14 am
content: This is obvious and you've doubtless checked, but just to be certain, the diodes are all installed in their correct orientation, right? Can you take a photo of the assembled board and post that?And to eliminate the possibility of the regulator tab being grounded, a quick check would be to remove the screw and lift it slightly off the board, then try applying power again.-Pat

author: eugenenine
author_rank: Frequent Contributor
timestamp: February 11, 2017, 01:50:44 am
content: I can't say I've ever seen a snubber cap in the middle of a bridge like that.You could de-solder r1 to isolate there. If you get good results left of R1 with it removed then that half is ok.

author: M4trix
author_rank: Frequent Contributor
timestamp: February 11, 2017, 01:53:05 am
content: Speaking of which, regarding the schematic document. Why do you have unnecessary junctions at the end of some component pins ? That usually happens when you rotate components, drag or flip them while they are connected with wire.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 03:24:59 am
content: Quote from: sleemanj on February 11, 2017, 12:29:18 amHey there,Thanks is the best way to check is just use continuity function on the DMM? E.g., check gnd against c6_1 etcSent from my 486 IBM WIN 3.1x Desktop...

author: sleemanj
author_rank: Super Contributor
timestamp: February 11, 2017, 03:52:14 am
content: Quote from: goldfinger on February 11, 2017, 03:24:59 amOr resistance. But if you are doing this on a populated PCB you will have to think about how components could affect the measurements.For starters though, break out your magnifying glass and a good light source and take a close look.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 04:17:48 am
content: Quote from: Cubdriver on February 11, 2017, 01:44:14 amYup I'll remove soon and check with the regulator off board. I'll post a pic tooCheersSent from my 486 IBM WIN 3.1x Desktop...

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 04:19:15 am
content: Quote from: M4trix on February 11, 2017, 01:53:05 amI would say rotation is probably the reason as mentioned pretty new!!

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 04:23:09 am
content: Quote from: sleemanj on February 11, 2017, 03:52:14 amI've actually got two unpopulated boards I could look at. If I'm using a bare board and I'm looking for power net referenced to ground with very little or no resistance?

author: Cubdriver
author_rank: Unknown
timestamp: February 11, 2017, 06:17:34 am
content: Quote from: goldfinger on February 11, 2017, 04:23:09 amIf you have bare boards, I'd do resistance checks between ALL the traces and ground. NOT finding a short doesn't rule out a manufacturing defect that happens to be only on the board you populated, but if you DO find one it would definitely be something specific to look for on the populated board.-Pat

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 07:28:10 am
content: Well, I've done a few things and not much luck. Removed the regulator from heat sink no change.Got a board and couldn't find any links between gnd and nets.Diodes for rectification all seemed ok measuring forward v only.I cut the link to R1, tried desoldering and it was a prick so just cut one side of it.Even after I cut the link to it and tried measuring just after the rectification I was only getting up and down mv.The secondary wires were also getting hot as if it was drawing too much current!So with R1 removed it has to be around the ac entry/rectification area.As even cutting off the rest of the circuit it still got issues.At loss what to try next. Should I build a new board with just the entry and 4 diodes and then measure to see if it's still the same issue?Sent from my 486 IBM WIN 3.1x Desktop...

author: sleemanj
author_rank: Super Contributor
timestamp: February 11, 2017, 07:37:39 am
content: If R1 is removed then.Remove C1Still problem?Remove C2Still problem?Remove diodes.Still problem?If you build up a second board, test as you go.

author: Cubdriver
author_rank: Unknown
timestamp: February 11, 2017, 08:15:53 am
content: 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 justoneof the secondary windings and see what happens.-Pat

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 08:23:00 am
content: 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!Sent from my 486 IBM WIN 3.1x Desktop...

author: Cubdriver
author_rank: Unknown
timestamp: February 11, 2017, 08:37:51 am
content: Just the diode bridge? What diodes are you using? Is it possible you've inadvertently used zeners in the bridge?-Pat

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 08:46:43 am
content: Quote from: Cubdriver on February 11, 2017, 08:37:51 amYeh just the ac/D.C. D1-d4 here's the onesI used had lying aroundhttp://au.mouser.com/Search/m_ProductDetail.aspx?r=625-SB5H100-E3

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 08:52:29 am
content: Quote from: Cubdriver on February 11, 2017, 08:15:53 amHey 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 operationsSent from my 486 IBM WIN 3.1x Desktop...

author: Dubbie
author_rank: Unknown
timestamp: February 11, 2017, 08:56:59 am
content: Seems like the transformer wiring might be suspect. Double check what you are doing there with a meter.

author: Cubdriver
author_rank: Unknown
timestamp: February 11, 2017, 09:00:14 am
content: 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

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 09:00:19 am
content: Quote from: sleemanj on February 11, 2017, 07:37:39 amYup that's what I did and with just d1-d4 on board issue straight away

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 09:06:23 am
content: Quote from: Dubbie on February 11, 2017, 08:56:59 amMeter 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

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 09:23:24 am
content: Quote from: Cubdriver on February 11, 2017, 09:00:14 amHey 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 20vacThe 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!

author: Rerouter
author_rank: Super Contributor
timestamp: February 11, 2017, 09:28:48 am
content: Only connect 1 secondary, and see what you get, like many other posters, you likely have mismatched secondaries, or have them connected antiparrellel.

author: neil t
author_rank: Regular Contributor
timestamp: February 11, 2017, 09:45:00 am
content: 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.

author: neil t
author_rank: Regular Contributor
timestamp: February 11, 2017, 09:58:34 am
content: the colour coding your showing matches a toroid I have in my handthe secondary's are orange yellowblack redif 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 ohmsregards Neil

author: Spuddevans
author_rank: Unknown
timestamp: February 11, 2017, 10:08:55 am
content: 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 atbothtop and bottom of the transformer and thereby creating an effective short-circuit turn which will make your transformer unhappy.Tim

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 10:36:19 am
content: Quote from: neil t on February 11, 2017, 09:45:00 amHi Neil,Sorry I realized my previous post might be confusing.Some photos referred to this transformerFor this transformer I had yellow and black as secondary taps (with red and orange jumpered)To be series 24v instead of 12Primary brown and blue as primary wires and violet and grey tied together.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 10:40:02 am
content: Quote from: Spuddevans on February 11, 2017, 10:08:55 amHi 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

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 10:56:27 am
content: Quote from: neil t on February 11, 2017, 09:58:34 amSent from my 486 IBM WIN 3.1x Desktop...

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 11:01:19 am
content: 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...

author: neil t
author_rank: Regular Contributor
timestamp: February 11, 2017, 11:21:48 am
content: Quote from: goldfinger on February 11, 2017, 11:01:19 amit 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

author: Spuddevans
author_rank: Unknown
timestamp: February 11, 2017, 11:33:54 am
content: 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

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 11:47:21 am
content: Quote from: neil t on February 11, 2017, 11:21:48 amHi 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 1.5ohmToro Transformer - 20vac 1A secondary beeps on continuity for the both of the taps, measures 1ohm

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 11:55:58 am
content: Quote from: Spuddevans on February 11, 2017, 11:33:54 amHey 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

author: neil t
author_rank: Regular Contributor
timestamp: February 11, 2017, 12:04:03 pm
content: Quote from: goldfinger on February 10, 2017, 10:45:34 pmLooking 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

author: sleemanj
author_rank: Super Contributor
timestamp: February 11, 2017, 12:26:52 pm
content: 1. On the pcb with diodes only (and without the transformer connected), confirm that there is no continuity between ac1 and ac22. take a picture showing exactly how you have the transformer wired to the pcb with diodes only

author: rsjsouza
author_rank: Super Contributor
timestamp: February 11, 2017, 01:17:04 pm
content: One thing I would do is connect the transformer to one of your empty spare boards and see what happens. If the PCB house made a boo boo in the fabrication, it would be evidenced by the transformer overheating with no parts inserted.I would then add a pair of diodes, connect and test; then the other pair, connect and test and so on.

author: Spuddevans
author_rank: Unknown
timestamp: February 11, 2017, 01:47:25 pm
content: Try connecting just one of the secondary windings to the PCB (ie not the two windings in series, leave the other winding un-connected) and see if it still heats up.Did you measure the AC current flowing through the PCB?Tim

author: Cubdriver
author_rank: Unknown
timestamp: February 11, 2017, 05:49:21 pm
content: On the photo of the diodes only board, I see only one input terminal block installed. How are you connecting the transformer to the board? Perhaps a photo showing the connections would be helpful.-Pat

author: rsjsouza
author_rank: Super Contributor
timestamp: February 11, 2017, 07:54:35 pm
content: Quote from: Cubdriver on February 11, 2017, 05:49:21 pmThat is a good point. If you are connecting both wires of the transformer to "AC1" they will be shorted according to your drawings. You should have both "AC1" and "AC2" populated to connect the transformer.

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 11:04:54 pm
content: All,Firstly want to say a big thank you to everyone who offered advice and help. I've found the issue there is a defect on some of the boards under neath near the ac entry with some bubbling now it's only very small but it looks like gnd plane might have defect to ac net. Which explains why it happens on entry! Thanks all really appreciate everyone's time and help.Awesome!!!Sent from my 486 IBM WIN 3.1x Desktop...

author: goldfinger
author_rank: Regular Contributor
timestamp: February 11, 2017, 11:11:55 pm
content: Quote from: Cubdriver on February 11, 2017, 05:49:21 pmYeh I installed one and realized the tinned wire on the smaller transfomer was small enough gauge just to sit in hole mate snug to test so didn't bother

author: neil t
author_rank: Regular Contributor
timestamp: February 12, 2017, 12:36:58 am
content: Quote from: goldfinger on February 11, 2017, 11:04:54 pmExcellent, congratulations, who doesn't enjoy a good sluthing moment, I think there was a number of guys trying to lead you to that conclusion. It seemed so obvious from this side. but highlights to all of us the need for due diligence when fault finding ie: the need to start from the source or origins and follow a logical path, as head banging as it can be the absolute thrill of finding a fault and subsequent satisfaction of gained knowledge. excellent stuff which is one of the reasons I joined this forum.regards Neil

author: goldfinger
author_rank: Regular Contributor
timestamp: February 12, 2017, 12:39:51 am
content: Quote from: neil t on February 12, 2017, 12:36:58 amVery true Neil, and thanks for your help! As much as a pain in the butt it is/was at least I know now how to fix!!!Thanks again to you and everyone else for their help and feedback!!!Sent from my 486 IBM WIN 3.1x Desktop...

author: Cubdriver
author_rank: Unknown
timestamp: February 12, 2017, 01:25:11 am
content: Excellent! Happy to hear that you've found the problem.I hope you can correct the issue with a bit of exacto knife surgery.-Pat