Can anyone help me fix this circuit board please?

Thread Starter

DanielHowden

Joined Nov 8, 2019
65
Hi Les, I do read your comments regarding the safety of my bulb setup and I do agree with what you say. Please don't be offended when I tell you that I used the bulbs as I have shown them but I was super careful when attaching them and where I placed the bulbs keeping in mind your comments at all times.

The result of the test was that both bulbs lit dimly. I turned the lights off in my workshop so that it would show on a photo.

So you have said that if the lights lit dimly then there is a short on the 47nF capacitors so it looks like I should go ahead and replace those.

Daniel.

PXL_20231121_160031369.jpg
 

LesJones

Joined Jan 8, 2017
4,190
It looks like something inn the filter section is leaky but not a total short. It could be either of the two 47 nF capacitors, the varistor or the common mode choke. I would mostly suspect the varistor. You will probably have to remove components one at a time until the bulbs no longer light. I suggest starting with the varistor then the two 47 nF capacitors one at a time and finally the common mode choke. (Do not replace the components after removing them. ) Before you start removing components try leaving the board powered up for about 5 or 10 minutes, Switch off at the isolator then touch the filter components to see if one of them has become warm. That may show up the faulty component.
The two 47 nF capacitors in parallel will have a reactance of about 32 K ohms at 50 hz which would pass a current of about 13 mA through the lamps but I don't think that would even make the filaments glow dull red, Check that the lamps are marked 60 W. (If you have been supplied with 15 watt lamps they may glow with a current of 13 mA.)

Les.
 

LesJones

Joined Jan 8, 2017
4,190
The varistor, the two 47nF capacitors, the two 2.2 nF capacitors and the common mode choke. (The yellow thing between the two 47 nF capacitors.)
As both the lamps are about the same brightness it is unlikely to be the 2.2 nF capacitors as their junction is connected to earth. (Which is at about the same potential as neutral would be.)

Les.
 

Thread Starter

DanielHowden

Joined Nov 8, 2019
65
So I did the test to leave the unit turned on for 5-10 minutes. None of the mentioned components was warm to the tough.

The next step seems to be to replace the varistor so I will source one of those.

Daniel.
 

LesJones

Joined Jan 8, 2017
4,190
You don't need to replace the varistor at this stage. Just remove it. Before removing it make a note of any markings on it in case it turns out to be the faulty part. The same with the capacitors remove them one at a time, doing the tests after removing each one. The last item that you remove before the lamps no longer light will be the faulty item. Do not remove the 2.2nF capacitors at this stage. Don't forget to make the choke the last item you remove.

Les.
 

Thread Starter

DanielHowden

Joined Nov 8, 2019
65
Just an update, I took out the varistor today and tested the board - no difference as the bulbs still lit dimly.

I will next remove one of the 47nF capacitors and try the test again.
 

LesJones

Joined Jan 8, 2017
4,190
Next time you power up the board to to the board to do the next test can you measure the AC voltage between the outer two pins on the white 3 pin socket that the wires from the transformer primary would normally connect to.

Les.
 

Thread Starter

DanielHowden

Joined Nov 8, 2019
65
I'm sorry I have been away from this for so long, I had family to stay and this week I have been swamped by work.

As far as testing goes, I have removed and tested the board with one of the 47nF units removed and the bulbs still lit.

I now realise I have incorrectly done your test Les, I am sorry about that. I put my multimeter across The outside terminals on the main board feed, when I have just re-read your post and you wanted it on the output to the transformer. I do appologise, I will do that test tomorrow.

Daniel.
 

Thread Starter

DanielHowden

Joined Nov 8, 2019
65
OK, so a cool update. After taking off the second 47nF and plugging the main power to the board, the bulbs did not light. So I guess this means that one of the 47nF units was faulty, is that correct Les? If so I guess I should go ahead and buy some more and fit them back on. I did measure the voltage at the two output pins and I read 238v. I was expecting it to be higher, like 400+v. Does that sounds right?

Daniel.
 

LesJones

Joined Jan 8, 2017
4,190
Yes you need to replace that capacitor. I suggest also replacing the other 47nF capacitor. RS and Farnell list some 47 nF capacitors 600 volts AC working but they do not say that they are X rated. (Which they should be.)
You need to check the lead spacing to match the holes in the board if possible. Post a picture of the markings on the 47 nF capacitors abd measure the pin spacing.
I don't understand why you expected a reading around 400 volts. The input voltage would be about 415 volts and you had a lamp in series each leg and the faulty componente between the output side of the lamps. So you had 415 - 238 = 177 volts across the two lamps. So each lamp would have 88.5 volts across it and the faulty component had the 238 volts across it.

Les.
 

Thread Starter

DanielHowden

Joined Nov 8, 2019
65
Thanks Les, I'm sorry to have been slow on this for the past couple of weeks. Ill look at getting some X rated 47nF capacitors and start to put the board back together.

I guess a good thing to test would be to put the new components in and plug it in with the bulbs attached to make sure that they do not illuminate.

Daniel.
 
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