Mystery component

[ljcox]

I'm trying to help someone via "The back shed" forum with an Arlec timer. Basically, he wants to modifiy it to work on 12 Volt DC rather than 240 VAC.

He has very little electronics knowledge & I don't have one of the timers to examine myself.

All I have the work with are the photos he has posted.

I have no idea what the component is that is shown in the attached photos.

It is located at the top left hand side of the PCB in the second photo.

I'm about to ask him to measure it with his DMM, but I'm not confident about the result - given his limited knowledge.

Any assistance will be appreciated.

 

[JimB]

Looks like a small signal diode to me.

JimB

 

[ljcox]

Looks like a small signal diode to me.

JimB

Thanks JimB.
That's what I thought also, but I would expect a diode to have only one band.

My other thought was a gas discharge overvoltage protection device.

I'm about to ask him to use his DMM on Continuity to measue it.

I'm also intending to ask him to measure all of the DC voltages in another post (I can't ask too many questions in one post otherwise he seems to go into overload)

However, it is dangerous since it is supplied from the mains via the big 250 Volt cap you can see, then rectified by the 4 pin diode bridge.

So I hope he does not electrocute himself.

I'll give him some instructions as to how to do it safely of course.

 

[Sceadwian]

My other thought was a gas discharge overvoltage protection device.

I see what looks VERY like a D underneath the component, the silk screen mask can tell you lot. Tell him to get a better picture, or lean in there with an eye loupe and a bright light to find out what it is. For any 'back shed' experimenter I can't recommend the use of magnification more. A 10X eye loupe can actually be simply placed in front of common digital camera or cell phone to adjust it's focus to the centimeter range.

To determine how this device actually functions will require a lot more detailed photo's of both sides of the board, and an explanation of what the ribbon cable that's fed into it is attached to.

Regardless, this will not be a simple modification, and definitely not something good for someone that doesn't have good descriptions of the circuit to tell someone that doesn't know what they're doing to do

 

[ljcox]

I see what looks VERY like a D underneath the component, the silk screen mask can tell you lot. Tell him to get a better picture, or lean in there with an eye loupe and a bright light to find out what it is. For any 'back shed' experimenter I can't recommend the use of magnification more. A 10X eye loupe can actually be simply placed in front of common digital camera or cell phone to adjust it's focus to the centimeter range.

To determine how this device actually functions will require a lot more detailed photo's of both sides of the board, and an explanation of what the ribbon cable that's fed into it is attached to.

I have several photos of both sides. I'm in the process of working out the circuit diagram.

Regardless, this will not be a simple modification, and definitely not something good for someone that doesn't have good descriptions of the circuit to tell someone that doesn't know what they're doing to do Yes, I know, but I'm prepared to persevere with him

Thanks for the comments. I'll pass a simplified version of them on.

I think JimB is right about it being Ge diode as it is connected to the base of the transistor. The other end goes into the ribbon cable.

So I assume the timer IC (see the photo) must hold the transistor off by applying a Gnd to the cathode of the diode. Hence the need for either a Ge or Schoktty.

 

[Sceadwian]

Why didn't you post those images to begin with? Starting to look like an avalanche diode rated to fail and shut down the transistor or something else on that external pin.

There are so many unknowns even at this point nothing can be determined.

 

[ljcox]

Why didn't you post those images to begin with? That's a good question. I guess I did not want to risk boring people with too much detail at that stage.Starting to look like an avalanche diode rated to fail and shut down the transistor or something else on that external pin.

There are so many unknowns even at this point nothing can be determined. I know, but I have to take him gradually, one simple step at a time. This morning, I asked him to tell me the resistor values & to measure the "Mystery Component" with his DMM set to Continuity & Diode test.

Thanks again for your interest. I'll let you know the result of my latest questions. I can't do any more until he answers them. Then I'll ask him to measure the voltages (with fingers crossed).

Here are 2 more photos.

 

[Sceadwian]

Did you have him take a sneak peak under the components? The silk screen should be visible if you catch it at the right angle.

 

[ljcox]

No, I didn’t.
As I said previously, he goes into overload if I ask too many questions/instructions.

I asked him to measure it with his DMM on the Continuity and Diode setting.

Also, I asked him to tell me what the resistor values are by reading the colour bands and by measuring them with his DMM.

Hopefully he will do all of this, but I won't hold my breath - given my past experience with him.

I have not yet had a response, so I’ll post his reply when received.

I'll ask him about the designation under the device later.

Thanks for your continuing interest.