Triac BT136 pin-out on PCB

[jh20]

Hi, referring to the picture in the attachment, can someone please advise which way a Triac BT136 (TO-220 package) should be mounted. Thanks.

[redwire]

Re: Triac BT136 pin-out on PCB

I can't quite tell from the pcb silkscreen. The heatsink will tell you more, which way the tab faces, if it has a heatsink.

What I'd do is look for the gate circuit, it would connect to all the little parts D3, R8 etc.
That puts the gate near EC1 etc. and so the tab would be facing the pcb edge. A pic of the pcb backside would confirm it, or you can trace the gate lead.
MT1, MT2 would have heavy high current traces.

BT136 pinout is MT1-MT2-G, tab is MT2.

[jh20]

Re: Triac BT136 pin-out on PCB

Thanks redwire. First of all, wow, how did you know the gate is near EC1? You must be very familiar with this type of circuit? You're the right man I was looking for

I've attached a few more photos for references. First one is the full view of the dimmer pcb with the Triac still on the pcb. Again you were right, the tab was facing the pcb edge. And you can see the Triac was blown.

The second photo is the back side of the pcb.

So, what was my problem? Well, look at the third photo which is a schematic I drew. The left half showing the Triac part of the circuit I traced and you can see straight away something is wrong. It should have been like the circuit shown on the right half where the Triac MT1 and Gate should be the other way round.

The forth photo is a very similar circuit I found on the net and it's like the right half of the schematic, except the AC Neutral did not have the coil (ec2) but connected directly to MT1 and pin 7 of IC1. The fifth photo is another similar but much clearer diagram I found.

Can you verify whether my finding was correct from the photo of the back side of the pcb? I've double checked my tracing, but just in case I really did made a mistake. If I was right does that mean the factory made a mistake with the Triac? The lamp belong to my grandson and he said it was working properly before it blew. This really got me confused and unsure if I was wrong

By the way, the 33K ohm 2W resistor on the other side of the pcb has also open circuited. It is equivalent to the 40K 2W resistor in photo 5, which is part of the Vdd (6.8Vdc) supply rail circuitry to IC1.

[stj]

Re: Triac BT136 pin-out on PCB

well it was built by scumbags.
few things piss me off more in this trade than seeing a board with the parts not put on the board properly before soldering.
how fucking half-assed can a person get when they cant even bother pushing a cap or diode down before soldering it.

[R_J]

Re: Triac BT136 pin-out on PCB

It is very likely the ic on the small board is bad. So are you going to replace that with the TT6061

[jh20]

Re: Triac BT136 pin-out on PCB

It is very likely the ic on the small board is bad. So are you going to replace that with the TT6061

no, if the IC is bad I'll give up

We'll see when I get the Triac and 2W resistor in, on ordered. But before I put the Triac in, need to confirm which way the Triac should be mounted. I'll retrace the circuit again today when I have some time.

[R_J]

Re: Triac BT136 pin-out on PCB

Is BT136 the original triac? R8 (10k) seems to be connected between T1 and gate but if that is correct there is nothing else connected to T1 but the 10k
Maybe it is just the 1µf hiding the part in the picture, but is there a component between R7 and the triac?

This site has a similar board that seems to use the same chip on board ic https://www.ccoors.de/blog/fixing-a-tcm-211682/

[budm]

Re: Triac BT136 pin-out on PCB

Yeah, I do not see C6 (as shown in the diagram) connected between the Gate and the IC either, there are solder pads for the cap but I do not see the cap installed.
May be you should provide straight shot pictures of the board.

[jh20]

Re: Triac BT136 pin-out on PCB

Yeah, I do not see C6 (as shown in the diagram) connected between the Gate and the IC either, there are solder pads for the cap but I do not see the cap installed.
May be you should provide straight shot pictures of the board.

Ok, 3 more photos at slightly different angles hopefully should clear things up. By the way to avoid confusion by some readers, the last diagram loaded earlier was a similar circuit I found on the internet, it is not the diagram to my circuit.

Noticed there's another mistake on the board? There's 2 C3, the 1uf 50v electrolytic cap and a small ceramic cap (C6 in the diagram you were referring to I believe) hidden behind in the earlier photo.

The MT1 (should be the gate) is currently connected to the ceramic C3 and R7 (in series) and then to pin 8 of IC1, which logically should be the trigger.

I've re-traced the circuit again and still came to the conclusion that the Triac was mounted incorrectly, ie, MT! and gate the other way round.

@R_J, bt136 is the original Triac.

[budm]

Re: Triac BT136 pin-out on PCB

OK, after looking at the board layout, you are right, it does look like the TRIAC was mounted wrong.

[jh20]

Re: Triac BT136 pin-out on PCB

Thanks budm. Based on the diagram I drew, with the triac the wrong way round, could it have worked at all in the first place? The lamp is at least 5 yrs old and my daughter said it's definitely been working fine before it blew last week! Weird.....

[Agent24]

Re: Triac BT136 pin-out on PCB

well it was built by scumbags.
few things piss me off more in this trade than seeing a board with the parts not put on the board properly before soldering.
how fucking half-assed can a person get when they cant even bother pushing a cap or diode down before soldering it.

No no, that's all part of secret Chinese design, it's for extra cooling, so they can run the components that extra 1% closer to the limit...

[R_J]

Re: Triac BT136 pin-out on PCB

I can't see how it would work being mounted wrong, that other site shows a very similar circuit that seems to use the same cob

[jh20]

Re: Triac BT136 pin-out on PCB

@R_J, I was thinking maybe the original triac had a different pinout too. But I found the blown-off molding in the casing and is still in one piece, and it definitely says BT136 on the top line, 600E second line, and PN0506B4 on the third. Can't show a photo as the prints are too small and faint to be picked up by the camera.

@Agent24, that's a good one But there's other advantages of not pushing the components all the way in.

1) much easier to remove when you need to get the tweezer underneath the lead.
2) it won't burn the pcb when it blew, nor would it caused a burnt mark when it gets too hot just like what the 2W resistor did.
3) you can move the components out of the way inorder to see what's printed on the pcb, like the component number r7, c3 etc. That's what I did before taking those last photos
4) Most importantly, saving time (cost) as you don't have to worry about making sure they sit in properly.

So, you see, the Chinese are smarter lol.....

[R_J]

Re: Triac BT136 pin-out on PCB

I don't know which wires are which but I would guess that the yellow goes to the metal base, the 2 brown are common and blue is line and red is load, if that is correct this is a very special triac because it has been handling the load of the lamp through a gate that is rated with a maximum of 10mA

[jh20]

Re: Triac BT136 pin-out on PCB

Ya, I don't understand either. But seriously the photo with the triac still soldered on the pcb was how it was when I open it up.

FYI, the blue is the AC neutral, coupled with the inner brown wire (live) are coming from the wall plug. The outer brown going to the bulb centre contact, and the red is the return from the bulb casing contact (load as you put it?). And the yellow is going to the metal base.

If replacing the triac and resistor don't work, I'll replace the whole module. They can be had for peanuts from China:

https://www.aliexpress.com/item/Mayi...f0cb4a407fc-18

Probably should have gone that way in the first place. Anyway if replacing the triac and resistor don't work, that's what I'll do.

I'll let you know the results when the parts arrive...

[budm]

Re: Triac BT136 pin-out on PCB

$1.58? wow.
BTW, it is rated at 60W, so did someone put much higher Wattage lamp to cause it to blow the TRIAC?

[R_J]

Re: Triac BT136 pin-out on PCB

The lamp return had the choice of two paths, the triac's T2 through gate, the other was the triac's T2 through T1 and 10k 1/2w resistor.
Or they purchaced a bunch of triacs that were mfg. with T1 and G reversed

[jh20]

Re: Triac BT136 pin-out on PCB

@budm, the one I linked was rated 60w because it uses a small triac inside. There are others with higher watt but I just simply linked the first hit I had from googling. Besides we we're only using 30w Mirabella bulb so that's not a problem. The one we have is rated 150W, said so on the module cover.

@R_J, I'm going with they bought a whole bunch of triacs mfg with reversed T1 and gate...

[momaka]

Re: Triac BT136 pin-out on PCB

BTW, it is rated at 60W, so did someone put much higher Wattage lamp to cause it to blow the TRIAC?

Could be they installed CCFL or non-dimable LED lamp. Both of these may draw excess current at low voltage. I had to repair a lamp like this with a blown/shorted TRIAC. According to its owner, that one blew due to her grandkid cycling the light no/off/dim all the time. But who knows.