Non audio triac question

Status
Not open for further replies.
Jump to Latest
S

srinath

Member
Joined 2010
#1
I have a dead heating unit today in my house.
I pulled the board and I suspect the transistor like object in the board has gone to heaven.
Its got MAC8N CQ233 written on it.
Looking it up - its a triac - and what that may be I have no clue, however since I am too broke to spend $595 on a new board, I thought I'd trouble shoot this guy.

So what is that Triac and where can I get another, and I'll put up the pic of the whole board in a bit, someone can help me I hope.

Thanks.
Srinath.
 
#2
A triac,

is two thyristors in inverse parallel.

TRIAC - Wikipedia, the free encyclopedia

basically its a switch..when a signal is put on the gate the device conducts...
however its conduction is controllable like a dimmer switch on AC power.
http://lib.chipdip.ru/205/doc000205292.pdf

There is nothing "special" about a Triac its a standard electronic part..(assuming its the Triac that's faulty)
Sometimes you will find a Diac in Triac circuits.
http://en.wikipedia.org/wiki/DIAC
They tend to look like a glass diode.

Regards
M. Gregg
 
Last edited:
#3
Would there be anything else blown on a board that has a triac blown ?
Is there a better way to test it than to slap it in my transistor tester ?

And what would be the equivalent of a MAC8N CQ 223 - like what can I ignore - is a MAC8N any other numbers following it the same as it.

Thanks.
Srinath.
 
#6
srinath said:
Would there be anything else blown on a board that has a triac blown ?
Is there a better way to test it than to slap it in my transistor tester ?

And what would be the equivalent of a MAC8N CQ 223 - like what can I ignore - is a MAC8N any other numbers following it the same as it.

Thanks.
Srinath.
Click to expand...

What are the symptoms of this dead board? Load doesn't turn on? Doesn't turn off? Smoke & flames? Might be a fuse somewhere has gone. Might not be the triac at fault at all.

Here's a datasheet saying it's an 800V 8A triac; MAC8N is the important part of the number, the CQ223 is a date/location code. Simplest is to just buy another MAC8N as they're available, but there are others that look compatible like a BT137-800, BT138-800, BT139-800, BTA16-800, etc. Just make sure that it's rated for at least as much current, as much voltage and has the pins in the same order (MT1, MT2, G).

Don't kill yourself with the mains.
 
#7
MAC8N's are on the way.
So is a supposedly working Lennox white rodgers board.
I only test and solder. The install is done by a heat/AC tech. I just forked out 45 bucks, but I did riddle him with 400 questions. On sunday too. So its a bargain based on that.
Thanks guys, you guys are the best.
Srinath.
 
#8
Putting your Triac on a transistor tester,

It a non starter..🙂 (no good) won't tell you anything!

The best way is in a test circuit..but this leaves a bit to be desired.

How to test a triac. - Electronic Circuits and Diagram-Electronics Projects and Design

On AC each side of the triac is in conduction, look at the symbol on the drawing imagine two diodes that are turned on with the gate.
When you replace it get the pin out correct!

Regards
M. Gregg
 
Last edited:
#10
My guess,

Is that after you power the gate the lamp will stay on if you disconnect the gate, because the latching current has been reached (current through the lamp) is high enough to latch the Triac...thyristors latch up/on when the latching current is reached below that it will turn on and off if the gate is switched. This is on DC because there is no "0" point in the supply sine wave for it to turn off..ie it is not being tested on AC. 😀

Regards
M. Gregg
 
Last edited:
#14
Yeah, test it with a 12V AC source and a 12V incandescent lightbulb rated at less than 2A (25W) - that will ensure the triac doesn't overheat with no heatsink. However, wiring up the gate is slightly interesting - you need to put current into the gate in the direction that you expect current to flow through the triac (see the quadrant diagram in the datasheet I linked earlier) so you can't just switch it with DC. Easiest way to do that is put a resistor of a couple kilo-ohms between G and (I think) MT2. Connect the resistor, light comes on. Disconnect it, light goes off.

If you wanna be fancy, use a diac on the gate and an adjustable RC circuit - you'll have a dimmer.

If you want to switch a triac using a DC signal, you need something like a MOC3020. I'd bet there's one of those (or equivalent) on the board you have so you probably want to make sure that that is also working correctly.
 
#16
srinath said:
That whole link from Onsemi - they dont say which pin is which.
It says 1, 2, 3 and 4 (mounting ear) but not what is MT1, MT2 and G (logically is 1 = MT1, 2 = MT2 and G is 3 and its the case as well ?

Thanks.
Srinath.
Click to expand...

Yeah, it's a really shitty datasheet. However, see Page 6 with the physical dimensions and it lists the pin name/number mapping just below the dimensions table:
1: MT1
2: MT2
3: GATE
tab: MT2
 
Status
Not open for further replies.
Top Bottom