Pool Solar Controller not working what part is this

[RedXT]

I have a heatseeker ss2d solar pool solar controller, normally shows roof temp and pool temp,and can be set to shut pump off at desired temp but now pool light just flashes and no display.
the part at Q2 seems to have failed, can anyone tell me what is is or is it not worth replacing





thanks thomo

[RedXT]

Looking a bit closer there is a similar transistor with c33740 ph91 would that be the same

[hinekadon]

never seen a transistor go like that .would suggest it may be a scr that cooked its self but no circuit dia makes it a bit hard

[george65]

The part will be cheap, knowing what value it is will be the trick. Can't read what value it is and I doubt the manufacturers if they are still around will tell you. You could try one of the electronic forums or google the make and model with problems after it.

I went up to the Gold Coast at Easter. Mates ancient pool Chlorinator wasn't working. He rang the company and they quoted him $400 to fix it. He asked how could they quote him without seeing to know what was wrong. Don't matter, flat rate, we'll just give you a recoed one. He rang me and I said tell them to jam it, they are nothing more than a rectified power supply. I threw in some Diodes and bridges in my bag and took them up with teh soldering iron. Tested the diodes, sure enough. Removed the old ones, Put in a bigger bridge and was done in about 15 Min. worked perfectly.
Mate was happy to reimburse me for the parts. Ok, $2 thanks.
I did touch him up on the price because the part was only about half of that but i'm just that kind of Miserable guy. ;0)

[RedXT]

The unit is 18 years old and I havnt been able to find a wiring diagram.
I removed it and it appears to be BC550C it goes in Q2 on the board, before this failed when I pressed the "Select button" on the controller it used change the temp display from "pool to roof".
At the moment the pool light is just flashing on and off.
I found these
unless someone out there has one or knows where I can get one
So I suppose I could try one, havent got much to lose

This is the board

cheers thomo

[fandtm666]

if there is a jaycar near you mate they have them for $0.38

[RedXT]

if there is a jaycar near you mate they have them for $0.38

Yea thanks about 30ks and they have then in stock

thanks

[BCNZ]

Rare to see a small-signal transistor melt like that.
It's obviously been passing some high current for a long time, but not quite so high that it immediately kills it.
If you look at the copper track you can see the wiper of the preset is feeding the centre pin, which on a BC550 is the base so
it's more likely to be one of these than an SCR.
The c33740 ph91 you mention is a BC337.
It could potentially be one of those as well because they have the same pin out - looking from the front of the transistor with the flat towards you it is C - B - E.
The 337 has a higher current rating than the 550.
Both are NPN.
It looks like the emitter is connected to a ground line, and the collector to a resistor but I can't read the value.
With time it wouldn't be hard to trace the rest of the circuit out to see what the transistor does and where it sits in the circuit.
The difficulty at this point is knowing how much current it potentially has to deal with.
If it's more than the rating of the BC550 (100 mA) it will fry it.
The BC337 is rated to 800 mA so this might be the better option to go with.
Jaycar sells these as well.

[hinekadon]

I concur with Studio1 ,bc337 will be better . but I cant see where the current to melt it has come from , assuming that the emmiter goes to ground , Whats the value of the collector resistor? that type of burn up is rare they normally blow the side out on a short , but this ones a slow melt , a bit hard case , the bump on the top makes it unusual as well . Thanks for the interesting problem !!!!

[RedXT]

after removing it with a magnifying glass I can read c55 something and c on the end and underneath starts with PH I took a picture but u cant read it.
I know very little about electronics but I new this wasnt right.
The roof sensor has been playing up sometimes and has a possible short at the end when I tested it with an OHM meter as per the manual instructions

[Uncle Fester]

I can see a fair bit of current flowing through that transistor if AC was applied to the sensor inputs.
Also a sudden very powerful static discharge on the said inputs.
How can you see if it is a 550C if it is melted like that?
It could also be a 560C, pnp.
The reason I am questioning that is that the negative terminal from the lower filter cap could be connected to the collector over that low ohm resistor(blue). I can't see the copper tracks properly.
You need to measure the voltages to determine if it is a pnp or npn type.

Edit, saw your last post after I submitted this. BC556 558 559 are all pnp too.
I would check the voltages on the transistor pads.

[RedXT]

from above post : Edit, saw your last post after I submitted this. BC556 558 559 are all pnp too.
I would check the voltages on the transistor pads.

yea i am only guessing

whats the worst that can happen if I put a 550C in?

[Uncle Fester]

from above post : Edit, saw your last post after I submitted this. BC556 558 559 are all pnp too.
I would check the voltages on the transistor pads.

yea i am only guessing

whats the worst that can happen if I put a 550C in?

It breaks.

Why risk it? Just switch it on and measure across the pads. If the collector(blue resistor) is negative against the emitter(1K resistor) then it is pnp, get a BC559. If it is positive use the BC550.

[RedXT]

It breaks.

Why risk it? Just switch it on and measure across the pads. If the collector(blue resistor) is negative against the emitter(1K resistor) then it is pnp, get a BC559. If it is positive use the BC550.

As I said I dont know much about electronics, U mean Like this Procedure of a Transistor Tester Using a Digital Multimeter

[RedXT]

this is what I found

[Uncle Fester]

Excellent. It is a pnp then.
Ask Jaycar for a BC557C. If they only have BC557B just get a few and find one with he highest hFE. Even the cheapest multimeters can test that but the BC557B generally seems to have a higher hFE range than the other BC55xC and it also can handle a higher voltage, which is more my concern than the higher current Studio1 suggested.

Because of the violent death the transistor experienced I would suspect other issues as well.
Have close look at that trim-pot, does that look a bit burnt on the right or is that fixing paint? Check that it has 500Ω.
The black cap above the blue resistor, I would just grab a new one from Jaycar and replace it and be aware of the polarity.
Measure the diodes to see if they are not shorted and show 0.3-0.7V forward voltage in the diode test mode of your meter.
The diode next to that (often mentioned) blue resistor, just below the small black cap, could be a zener diode because it's cathode appears to be connected to the positive side of the cap.
If the trim-pot is damaged then that zener probably need replacing too. You would probably need to solder it out, at least on one leg, to read what is on it. 50% chance that it has a 5.1V rating.

[hinekadon]

looking at the last b/d it would appear that the sensors are a ptc type and the pool one has a (short) on it and therefore the cooking of the transistor perhaps you should proceed with this approach before you change the transistor , cos if you dont it will go poof on you as it only has a 1k resistor in series with the emiter current , the base appears to be pos as theres no load on the pot without the transistor in circuit cheers don

[RedXT]

Excellent. It is a pnp then.
Ask Jaycar for a BC557C. If they only have BC557B just get a few and find one with he highest hFE. Even the cheapest multimeters can test that but the BC557B generally seems to have a higher hFE range than the other BC55xC and it also can handle a higher voltage, which is more my concern than the higher current Studio1 suggested.

Because of the violent death the transistor experienced I would suspect other issues as well.
Have close look at that trim-pot, does that look a bit burnt on the right or is that fixing paint? Check that it has 500Ω.
The black cap above the blue resistor, I would just grab a new one from Jaycar and replace it and be aware of the polarity.
Measure the diodes to see if they are not shorted and show 0.3-0.7V forward voltage in the diode test mode of your meter.
The diode next to that (often mentioned) blue resistor, just below the small black cap, could be a zener diode because it's cathode appears to be connected to the positive side of the cap.
If the trim-pot is damaged then that zener probably need replacing too. You would probably need to solder it out, at least on one leg, to read what is on it. 50% chance that it has a 5.1V rating.

As a retired motor mechanic this is all new to me but I like to learn new things, I will get some parts and go from there
Thanks everyone for you're response so far, I will let u know what happens

cheers thomo

[Uncle Fester]

looking at the last b/d it would appear that the sensors are a ptc type and the pool one has a (short) on it and therefore the cooking of the transistor perhaps you should proceed with this approach before you change the transistor , cos if you dont it will go poof on you as it only has a 1k resistor in series with the emiter current , the base appears to be pos as theres no load on the pot without the transistor in circuit cheers don

I can hardly see the transistor going up like that with a short on the inputs. Somebody accidently connecting 240V seems way more likely.

However you are very right to inspect what is/has happend and have a very close look at the input wiring and also check for shorts.

[RedXT]

I can hardly see the transistor going up like that with a short in the inputs. Somebody accidently connecting 240V seems way more likely.

However you are very right to inspect what is/has happend and have a very close look at the input wiring and also check for shorts.

Not that I know of, its been screwed to the wall for 18 years and only took it off the other day when it stopped working, took the front off and found the transistor like it is