Ah.. could well be shorted; is that in circuit or out? In-circuit you could be measuring the LM324 as well... Take ZD1 out of circuit by lifting one end and retest. If you can read any numbers on it that would be useful.

 

It was taken out : I measured it with the ohm-meter : I get 5.6 and 3.8 ohms ... It is also not possible to read the model ... it starts with C and ands with PH27 ... in between impossible to read !

 

Yes, its fried...

Replacement is a BZX55-C27 or any 27v 0.5W DO-35 glass Zener diode

 

I will buy a kit on amazon so that I will have many choices I was considering mounting the LM342N on a socket instead of the direct PCB connection. Any disadvantage ?

 

Hi Irving, a delayed merry xmas to you and your beloved ones. I have finally received the ICs, the zeners and the socket (guess they were stuck somewhere in the red sea . I will re-mount the components on the PCB.

I wonder if, before trying to power up the heater, there are sensible tests I can/should perform.

Thanks

 

Hi Irving, a delayed merry xmas to you and your beloved ones. I have finally received the ICs, the zeners and the socket (guess they were stuck somewhere in the red sea . I will re-mount the components on the PCB.

I wonder if, before trying to power up the heater, there are sensible tests I can/should perform.

Thanks

Thanks & likewise for the coming new year.

Without the LM324 installed, power up the board and check voltage across ZD1, should be 27v +/- 1v DC, socket pin 4 to pin 11 should be same.

If you are very careful, jumpering socket pin 4 to pin 7 should turn fan on at full speed, assuming tilt switch not activated. Otherwise fan should be off.

If that looks ok, power off. Short socket pin 4 to pin 11 to discharge the capacitor, then insert the LM324, carefully making sure of orientation.

Power up again. Check voltage across ZD1, should be much as before. On manual mode VR1 should control fan speed and the DC voltage at the gate of the Triac, at the junction of the 100R and the 2k2 should vary from around 5v to 15v maybe more.

 

Thanks & likewise for the coming new year.

Without the LM324 installed, power up the board and check voltage across ZD1, should be 27v +/- 1v DC, socket pin 4 to pin 11 should be same.

If you are very careful, jumpering socket pin 4 to pin 7 should turn fan on at full speed, assuming tilt switch not activated. Otherwise fan should be off.

If that looks ok, power off. Short socket pin 4 to pin 11 to discharge the capacitor, then insert the LM324, carefully making sure of orientation.

Power up again. Check voltage across ZD1, should be much as before. On manual mode VR1 should control fan speed and the DC voltage at the gate of the Triac, at the junction of the 100R and the 2k2 should vary from around 5v to 15v maybe more.

Thank you Irving ... I am already sweating fortunately I was forced to buy 10 LM and 10 Zeners ! Will go forward as per your instruction !

 

Before plugging in the LM324 it might be wise to check voltages on all pins of the socket. both DC and AC. nothing should be >27v DC or approx 21v AC

 

Hi Irving, here the latest news:

1) Successfully soldered the new ZENER and the SOCKET
2) Connected PCB to heater and powered on
3) Tension ZD1 and across P4-P11 perfect approx 26 volts
4) Jumpering P4 to P7 successfully started the motor at full speed
5) Power Off & Capacitor discharged
6) LM324 Plugged in and Power ON
7) Nothing happened ! No tension across ZD1 and P4-P11 anymore
8) Detach ZD1 and measure : GRILLED :-(

Having read you recommendation of checking AC/DC voltage across all pins too late, I did it after having replaced the ZENER. The voltage was measured between GND and the various PINS. Here the results:

I have replaced the ZENER but did not plug in a new LM yet: i guess there is an additional issue, might be another Zener ... I'am trying to do a qualitative analysis ...

PIN 1-7	PIN 7-14
1 0	8 12V AC 40V DC
2 0	9
3 28V AC 14V DC	10
4 59V AC 26V DC	11
5 14V AC 8V DC	12 15V AC 40V DC
6 10V AC	13 10V AC 6V DC
7 12V AC	14 12V AC 4V DC

 

Hmmmm, interesting...

ZD1 is fried, and/or the LM324?

Are you running 220 or 110v AC?

What is the value of the electrolytic cap?

 

Hmmmm, interesting...

ZD1 is fried, and/or the LM324?

Are you running 220 or 110v AC?

What is the value of the electrolytic cap?

ZD1 kind of fish and chips ! Already replaced. No clue about LM, will probably build a test circuit for investigation.

Running 220

Cap is 100uf / 50V

I should probably recheck capacitor and all the diodes: will this help ?

 

Yes, recheck everything, and confirm values of parts as below

 

Yes, recheck everything, and confirm values of parts as below

View attachment 311251

I will do it soon ! I was looking at your simulation : could you please send me the nlist of the opamps so that I can play with it in KICAD / ngspice ? I am trying to improve my skills around opamps but I am unsure about my test circuit (one opamp).

HAPPY NEW YEAR !

 

I've not used the simulator in KiCAD, I'm much wedded to LTSpice though the graphics are not as nice... must have another go with it.

Not sure what you were trying to simulate there, but applying 200+V directly to the LM324 will instantly fry it, I guess the zener was an attempt to reduce that but its not in the right place or the right way round.

 

I've not used the simulator in KiCAD, I'm much wedded to LTSpice though the graphics are not as nice... must have another go with it.

Not sure what you were trying to simulate there, but applying 200+V directly to the LM324 will instantly fry it, I guess the zener was an attempt to reduce that but its not in the right place or the right way round.

Just playing around to check nspice reactions

 

Yes, recheck everything, and confirm values of parts as below

View attachment 311251

Hi Irving
I checked the resistors, zeners and capacitor (no desoldering) and they look ok with the following exceptions:

1) The two resistors show 50k vs 100k
2) the small zener looks bad

What you reported as 1 Meg should read 100k vs. 1Meg if I am not mistaken.

I have now access to my oscilloscope and will try (without putting the LM back) to look at the small zener.

 

DO NOT CONNECT YOUR SCOPE WHILE MAINS POWER applied, you run a good risk of blowing it up.

Your scope probe earth is connected to ground (PE) but your circuit's "ground" is mains neutral which is potentially 110v AC wrt PE.

Using a scope to diagnose AC issues must only be done with a isolation transformer or a differential probe.

 

the small zener looks bad

It's not a zener (i don't think) .. But bad in what way?

 

It's not a zener (i don't think) .. But bad in what way?

It looks like a zener : measuring it in both directions in diode and resistor mode gives almost 0.

 

It looks like a zener

All glass diodes look the same, but its designation on the board is D not ZD,I believe.

measuring it in both directions in diode and resistor mode gives almost 0.

then its shorted out... are there any markings on it?