OK, the DC voltage is jumping around too fast for my DVM to read. It shows slightly above one volt up to nearly four volts. Next test is to put the scope on it. Scoped, it is reading 24 VDC ONLY when the relay is clicking. I think the next step is to remove the relay and retest for voltage on those pins. If the voltage is stable without the relay in place then the problem may be the relay. If not - then the board is either searching for some back signal or the board may just be bad. I may have to live without the relay.

{update}

With the relay removed and measuring only the board and the applied voltage at the relay coil leads, every 28 seconds it begins a new cycle of trying to start the relay. It's doing it with and without the relay in stalled. So it's not the relay.

 

It's doing it with and without the relay in stalled. So it's not the relay.

I would agree with that!
Max.

 

Your ohmmeter could be used to figure out which winding is connected to a rectifier and which winding is connected to mains input.

That's the obvious first place to start - I'd put a fridge bulb in series with the highest resistance winding to limit the current and power it up. You should at the very least get an indication of the ratios.

Some transformers have identical dual primaries that can be series or parallel for 220 or 110V - but I've never seen that on a UK 230V microwave PCB transformer.

 

Pin 1 of the relay is connected to a 33KΩ resistor that feeds to pin 1 of an optoisolator. I wonder if there's supposed to be a signal there. IF there's a 120 VAC signal then that would be 3.6 mA going to the opto. Also going to that same pin 1 of the opto is a trace from P3 pin 2 (orange wire) that plugged into something - I haven't a clue. No resistors, just a signal diode into pin 1 of the opto. There is a resistor bridging P3 pin 1 & 2, a 33KΩ resistor but I don't know what it's looking for. Maybe 120 VAC on pin 1? It's a very small resistor, can't be more than a half watt. It's slightly bigger than my quarter watt resistors. IF I push 120 VAC through that resistor to the signal diode and into the opto, that's 3.6mA x 120 VAC, that's going to be 432 mW. Less than half a watt, but kind of cutting it close. Unless the source of the signal is providing some resistance.

I found a broken 1N4148 diode and replaced it but that changed nothing. And I'm not even sure if I damaged it while handling the board. Nevertheless, fixed - no change.

 

Could it be I have my hot and neutral reversed? I've assumed P9 to be the hot because it's connected to the Triac. Pins 12 & 13 I've assumed to be neutral, but there is a resistor leading off from there (68KΩ) to the same opto. I'm just afraid of reversing the polarity and blowing something up. That'd stink because I'm getting close to making this thing do something, though as yet I haven't decided what to do with it.

 

The board is fairly sparsely populated but is has a LSI chip on it which may make it difficult to otherwise reverse-engineer it.
Reversing the neutral should not affect anything.
Max.

 

I'm just a little stumped by the relay. Pin 2 is connected to nothing but a spade lug. Pin 1 is connected to a spade AND to the PCB. From there it goes a couple different places. Working on photos now.

 

If this is a microwave, how were the interlocks taken care of? Usually there are three. One shorts the power and the other two are in series allowing power to the oven.

What about the turntable that's used in some microwaves. I can't think of why it would cycle.

 

How were the interlocks taken care of?

Good question. Hadn't thought of that before. Must be those extra wires I have on a plug. But I've tried shorting them and leaving them open. Maybe I'm going about that the wrong way. maybe P3 pin 2 is supposed to be powered. Still working on photos.

 

Good question. Hadn't thought of that before. Must be those extra wires I have on a plug. But I've tried shorting them and leaving them open. Maybe I'm going about that the wrong way. maybe P3 pin 2 is supposed to be powered. Still working on photos.

The interlocks are usually industry standard micro switches. As someone already mentioned; 2 of those are in series with the mains. The 3rd is the failsafe - if both the series switches weld, the shunt switch shorts it out and blows the fuse.

 

Working out the kinks. I have an A1266GR (transistor looking device) I can't find a data sheet for it. What I found was for a hall effect switch. This can't be a HE Switch. IT only has three leads and the data sheet shows five leads and is a flat pack SMD.

Here's a copy of what I have figured out so far: (see lower right corner)

 

Sure it is not a 2SA1266?
Looks like it may be switching the relay next to it.
Max.

 

Sure it is not

It's

K033
A1266
GR

No other markings and it looks like a three lead PNP transistor. (PNP because I just found someone selling the device - but no data sheet).

 

Sure it is not a 2SA1266?
Max.

Most likely. The '2S' part is often omitted.

 

It's

K033
A1266
GR

No other markings and it looks like a three lead PNP transistor. (PNP because I just found someone selling the device - but no data sheet).

There's some date here: http://www.datasheets360.com/pdf/2270432959039860787

 

http://www.datasheets360.com/part/d...32959039860787/?alternatePartManufacturerId=0
Oops.. beaten to it!
Max.

 

It's

K033
A1266
GR

No other markings and it looks like a three lead PNP transistor. (PNP because I just found someone selling the device - but no data sheet).

The K could be a 2SK number, but if such a low number (zero prefix) even exists - it would more likely be a JFET.

A 2SA transistor is near guaranteed to be PNP.

 

On the Opto; if I jump pins 4 & 5 the oven stalls. It appears the circuitry is designed that if it gets a signal it disables the oven function. I'm still not able to isolate why the relay clicks rapidly for four seconds then repeats after 24 seconds. Apparently, the reason why this MO was scrapped was because it was no longer functioning. I just wish I'd have kept the schematic. Live and learn. It's probably not fixable. Can use as a timer and a clock. Can use the lamp and fan switches to operate low wattage devices. The fan is controlled via Triac and the light is controlled by a relay. If you look at the picture, pin 18 is connected to two relays. One supplies both sides of the sine wave while the other supplies only half wave. An incandescent lamp works great but an LED or CFL wouldn't function properly.

There's the 16 amp clicking relay (I think I labeled it as 8A) that I'd like to use for some major control - say run my soldering iron for a period of time and if I forget to shut it off - the timer would limit the run time. The other four relays (was very difficult seeing the ratings) (labeled as 1A relays), as I said, two of them control the light. The other two seem to activate the safety kill circuit. I can probably ignore them. They're fed 24 VDC from P3, pins 1, 2, 3 & 5 and I don't know where that power is supposed to come from. Unless there was more to that oven. This has been sitting in my cabinet for a few years, so don't expect me to remember such things. At the time I had no purpose for the panel other than maybe scrap it for parts. I like the fluorescent display on it. That's working.

At most this is an exercise in futility (for me). I could use it to control a fan or light but what would be wrong with using the switch on the fan or the light to control them? I can't run the timer and control the light/fan, all it ends up being is a switch circuit that affords full power or half power to the light/fan. I'm close to quitting on this. Maybe build a clock and a countdown alarm timer.

 

MY FINAL WORDS ON THIS PROJECT:

I've found a controlled 24 volt circuit and have jumpered it to the relay. It now clicks on and stays on for the duration of the cook cycle. I can connect that circuit (the relay switch) to run my soldering station. Suppose I want it on for an hour. Easy to set an hour and run it. If I forget to turn it off - no problem. I also have two other circuits that are button controlled. Turn them on and they're on till you turn them off. Can control a light and an exhaust fan (low wattage), up to 8 amps. (960 W or VA)

So now I have a new project: Build a box for this control panel along with a duplex outlet for controlling a light/fan and another outlet for controlling up to 1,920 watts. More than the amount of power I can expect from a 15 amp service.

Thanks all for your help. Oh, and I did mis-draw my diagram slightly. Had the bottom two relays drawn with the switch side where the control coil side should have been. Oops. Pays to double-check. But to do that I had to remove the relay and bench test it. And I'm leaving them out of the circuit. They're not needed.