I have mirrored the picture of the etch side of the board and started to show component connections. This is it.
The fuses supply the primary of the transformer and I suspect that they also go to the bottom end of the three resistors. Can you check if this is so with resistance checks ?
I don't know what the common top end of thse resistors connect to.
(After thinking about this comment I must be wrong.)
Daniel, Can you trace where the top end of resistors connect ?
Can you tell us if the machine has been working in it's present location and there have been no changes to the mains supply to it.
Do you know when and why the short link was soldered between the left hand pin of the power input connector and the large trach area I have marked as "neutral or earth" ?
Is the wire from the isolator switch to the left hand pin of the mains input connector earth or neutral ?
Can you measure the resistance of the middle one of the three resistors that looks undamaged to confirm it is 22 ohms as we suspect ?
The fact that the 380 volt tapping on the transformer is connected when you say your mains supply is 415 volts may have caused the fuses to blow but does not explain the resistor failures.
Can you check the markings on the 3 rectangular things to the right of the 3 resistors to see what their value is and the rated working voltage (I think they are capacitors.)

Les.

 

Be very careful with the Voltage differences.
This could have been the cause of whole problem in the first place.
I simply had to assume that the Machine has been working correctly for some period of time,
maybe this was a bad assumption to make.

Has the Machine been working correctly ?, and for how long ?

You can't get away with running substantially higher Voltage than the Machine is rated for,
parts are going to fail.

Another bad assumption .........
When You provided a picture of 3 identical Resistors, in a row parallel to each other,
( 2 of which have failed ),
and then stated that this Machine is supplied by 3-Phase-Power,
it is very logical to assume that each Resistor is connected to each separate Phase.
It is now obvious that this is NOT the actual situation,
So, determining the cause for the failure is the current priority.
Most likely the problem is excessively high Voltage being supplied.

As a side-note,
The Phase-Loss-Relay is also not rated for 415-Volts,
and will very likely fail if connected to that much additional Voltage.
AFTER the Voltage issue is resolved,
the wiring solution offered by Dodgydave above, is what I would also recommend.

You may have to purchase 3 Voltage-Adjusting-Auto-Transformers to
allow this machine to operate reliably on your available 415-Volt Supply.
.
.
.

 

Mains supply is 415v

There's a 415V tap on the transformer, it would be better to select this.

 

I have mirrored the picture of the etch side of the board and started to show component connections. This is it.
View attachment 307341The fuses supply the primary of the transformer and I suspect that they also go to the bottom end of the three resistors. Can you check if this is so with resistance checks ?
I don't know what the common top end of thse resistors connect to.
(After thinking about this comment I must be wrong.)
Daniel, Can you trace where the top end of resistors connect ?
Can you tell us if the machine has been working in it's present location and there have been no changes to the mains supply to it.
Do you know when and why the short link was soldered between the left hand pin of the power input connector and the large trach area I have marked as "neutral or earth" ?
Is the wire from the isolator switch to the left hand pin of the mains input connector earth or neutral ?
Can you measure the resistance of the middle one of the three resistors that looks undamaged to confirm it is 22 ohms as we suspect ?
The fact that the 380 volt tapping on the transformer is connected when you say your mains supply is 415 volts may have caused the fuses to blow but does not explain the resistor failures.
Can you check the markings on the 3 rectangular things to the right of the 3 resistors to see what their value is and the rated working voltage (I think they are capacitors.)

Les.

The fuses supply the primary of the transformer and I suspect that they also go to the bottom end of the three resistors. Can you check if this is so with resistance checks ?

I checked continuity and there was none, checking the three resistors and the two fuses going through a sequence, both ends, so that I have checked all combinations. (Doh, just read your following comment!)

Daniel, Can you trace where the top end of resistors connect ?

Can you tell us if the machine has been working in it's present location and there have been no changes to the mains supply to it.

Yes, the machine was working fine. I'm not aware of any changes to the supply I have.

Do you know when and why the short link was soldered between the left hand pin of the power input connector and the large trach area I have marked as "neutral or earth" ?

No, this is not my work. Maybe an oversight in the factory? The large area you refer to has no connection to anything at all. Its not even used as a fixing point with the two holes in it that have the silver square.

Is the wire from the isolator switch to the left hand  pin of the mains input connector earth or neutral ?

Yes, it is earth, so the short link is for earth purposes.

Can you measure the resistance of the middle one of the three resistors that looks undamaged to confirm it is 22 ohms as we suspect ?

I get a reading of 28.8 ohms

Can you check the markings on the 3 rectangular things to the right of the 3 resistors to see what their value is and the rated working voltage (I think they are capacitors.)

Hows that? They are all the same.



Hope all that helps, it was fun getting the answers for you.

 

Be very careful with the Voltage differences.
This could have been the cause of whole problem in the first place.
I simply had to assume that the Machine has been working correctly for some period of time,
maybe this was a bad assumption to make.

Has the Machine been working correctly ?, and for how long ?

You can't get away with running substantially higher Voltage than the Machine is rated for,
parts are going to fail.

Another bad assumption .........
When You provided a picture of 3 identical Resistors, in a row parallel to each other,
( 2 of which have failed ),
and then stated that this Machine is supplied by 3-Phase-Power,
it is very logical to assume that each Resistor is connected to each separate Phase.
It is now obvious that this is NOT the actual situation,
So, determining the cause for the failure is the current priority.
Most likely the problem is excessively high Voltage being supplied.

As a side-note,
The Phase-Loss-Relay is also not rated for 415-Volts,
and will very likely fail if connected to that much additional Voltage.
AFTER the Voltage issue is resolved,
the wiring solution offered by Dodgydave above, is what I would also recommend.

You may have to purchase 3 Voltage-Adjusting-Auto-Transformers to
allow this machine to operate reliably on your available 415-Volt Supply.
.
.
.

Got it, sorry if I haven't supplied all the information needed. Its just me not really understanding what the problem is.

The machine has been working for several months with no problems.

I will purchase a new PLR rated at the correct voltage.

 

There's a 415V tap on the transformer, it would be better to select this.

Thank you, I will do.

 

UK Mains Supply Voltages
The electrical supply that we connect to is supplied from a generating station or renewable power source through the National Grid. As the electricity moves through the grid its voltage is reduced through a series of sub-stations and eventually into the three phase and single phase power supplies we use.

The International Electrotechnical Commission groups the voltages (in IEC 60038) into the following categories:

• Low Voltage (LV) up to 1000Vac
• Medium Voltage (MV) from 1000V to 35kVac
• High Voltage (HV) from 35 to 230kVac
• Extremely High Voltage (-) above 230kVac

The electrical supply voltage is generated at a high level for a number of reasons including transmission losses within the National Grid distribution system.

Single and Three Phase Mains Supply Voltages
In 1995, electricity supply voltages in Western Europe were harmonised to 230Vac single phase and 400Vac three phase.

In the UK, the traditional single phase mains power supply voltage was 240Vac and in Europe the supply voltage was 220Vac. This has been harmonised to 230Vac +10% to -6%.

The traditional three phase mains power supply voltage was 415Vac and in Europe the supply voltage was 380Vac. This has been harmonised to 400Vac +10% to -6%.

The mains power supply voltage can vary dependent upon the time of day, local load and distribution arrangements.

A high mains power supply voltage can reduce equipment reliability. A low mains power supply voltage can lead to erratic server operation and potential crashes if the voltage levels falls outside the input voltage window of the switch mode power supply.

Uninterruptible power supplies provide a means to mitigate these risks and protect server room and datacentre environments from mains power supply problems.

I found this about the electricity voltages in the UK. Looks to me like I should assume 415v to be on the safe side.

 

Now that we know tha tyou are in the UK we also know the frequency is 50 Hz. With problems relating to mains supply it is helpful to give some idea of your location in your profile.
I have now traced out part of the schematic. I think you will have to try to do more as you have the board and can see more of the tracks on the component side and you can do resistance checks to help trace them.
Here is what I have traced so far.
I originaly thought that the fuses were connected to the three resistors but I can see no direct connection.
The three resistors are in series with the 1uF capacitor. I think this is a snubber circuit to suppress transients when the relay contacts open. These 3 snubber circuits are connected n a star configuration. (Like a star connected windings in a three phase motor.) With 415 volts pase to phase there will be 240 volts between the ends of each snubber network. The 1 uF capacitors will have a reactance of about 3.2 K ohms. This will be the main factor in determining the current through the resistors so the current will be 240/3200 = 0.075 amps. the votage across the 22 ohm resistors will be 1.65 volts and the dissipation about 0.12 watts. I thnk there must have been a high voltage transient between 2 phases on the mains to blow the fuses and burn the resistors..
This may have damaged other components. check that the 3 1uF capacitors have not gon short circuit or leaky. (They should read totaly open circuit on your meter after the initial charging surge.) Also check the resistance between the output end of the two fuse holders.
I suspect that the junction of the to 2.2nF capacitors connect to the large earthed area of track. can you check if this is the case.

Here is the latest picture of the componant connections on the etch side of the board.
From this I can see that one relay selects one direction of rotation and the other relay selects the other direction. Both relays MUST NEVER BE ENERGISED AT THE SAME TIME as this would short two phases together.

Les.

 

Les, I apologise again for not offering all of the information needed at the outset and I thank you for your interest here.

This may have damaged other components. check that the 3 1uF capacitors have not gon short circuit or leaky. (They should read totaly open circuit on your meter after the initial charging surge.)

When you say "initial charging sequence" are you asking my to power up the board again on the machine?

Also check the resistance between the output end of the two fuse holders.

When I check this I have an open circuit

I suspect that the junction of the to 2.2nF capacitors connect to the large earthed area of track. can you check if this is the case.

When I check this I have no continuity on any of the three capacitors.

 

Re checking capacitors. When you connect your meter set to a resistance range to a capacitor you will see it reading less than infinity for a very short time. This is because the test current from the meter needs to charge the capacitor until it has reached the voltage from the test leads. This will probably be for less than a second for a 1 uF capacitor.
Re the 2.2 nF capacitos. There are only two 2.2nf capacitors. They are just to the left of the bottom end of the 3 resistors above the upper 47nF capacitor. After looking at the component side of the board again so I could describe where they were They do seem to be connected to a larhe earthed section of track on that side.
Can you confirm that the lower end of each fuse holder connects to one phase of the mains input to the board.

Les.

 

Yes there is a connection there between the fuses and the power supply wires. I have indicated it here.



I don't appear to have a sophisticated enough multi meter to test the capacitors.

 

You only need a high resistance range (2M on the above meter.) We are only doing a test for a shorted capacitor. We dont need to measure the capacity or ESR (effective series resistance.)
Can you also measure the resistance between the two top fuse connectors (With neither fuse inserted) and then between each one and earth. (The left hand pin on either the power input or motor output connectors.)
Les.

 

Ok cool, I did that. Damn, it happened so quick I had to take a video.

https://photos.app.goo.gl/UDubLE1BavseFpR19

 

I'm not sure from the video if you tested just 1 or all 3 of the 1uf capacitors. The result you showed was what I would expect for a good capacitor. I only mentioned the initial readings in case you did not understand what was happening. I was expecting one or more of them to be short circuited
Have you done the tests on the mains input filter that I requested ? If so what was the result ? The capacitors in that circuit are lower value so the initial readings will last for about one tenth of the time.

Les.

 

Hi Les, I did the test on all 3 capacitors and got the same result. I'm sorry I didn't specify this, it happened so fast it caught me off guard.

Forgive my ignorance but I didn't see what test you requested when I looked back at the posts you have made. I'm afraid I don't understand what "mains input filter" means.

If you could explain, I will do the test immediately.

 

Mains input filters are to suppress noise and spikes on the supply, so they don't feed back down the mains,usually used on inductive loads like motors, and switch-mode power units, .

 

The mains input filter is the part of the schematic in the top left hand corner of post #29. It only filters the supply to the transformer which provides power to the display electronics.
The requested tests are in the last sentence of post #33.

Les.

 

OK, I videoed the result of measuring the resistance between the two top fuse connectors without the fuses in. This is the result. I got a result each time I took the test by reversing my probes each time.

https://photos.app.goo.gl/GjVPnZ2dWvR8CEAT8

When I tested from each fuse connector to earth as your description in #33, I get no continuity at all.

Hope I did this right Les, Daniel.

Edit: I am looking at Phase Loss Protection Relays and they have a Neutral connection to them. I don't have a Neutral connection on my power feed in, I just have 3 x L and an earth. I think I am not understanding something here.

 

I think the reading that you showed all seem OK. (It would have been better if you had given a commentary.)
The only thing I can think of that damaged the resistors was a high voltage surge between two phases but if that was the case I would have expected the varistor (The blue thing at the bottom left corner of the board.) to have failed short circuit. I am now wondering if the fuses blew at the same time as the resistors failed. The machine would have worked with the two resistors open circuit but it would have shoretened the life of the relay contacts. The fuses could have failed due to a short on the transformer windings or a short in the display unit. I don't think the loss of a phase would have caused either of these faults.
I would be interested in comments from other forum members. If I was working on the fault my next step would be to try just powering the electonics by connecting normal 240 volt mains to the 220 volt input of the transformer. I would fit a 2 amp fuse to the mains plug and wire a 60 or 100 watt filament bulb in series with the mains to limit the current. If this worked it would show that the transformer was OK and the was no short in the electronics.

Les.

 

I think the reading that you showed all seem OK. (It would have been better if you had given a commentary.)
The only thing I can think of that damaged the resistors was a high voltage surge between two phases but if that was the case I would have expected the varistor (The blue thing at the bottom left corner of the board.) to have failed short circuit. I am now wondering if the fuses blew at the same time as the resistors failed. The machine would have worked with the two resistors open circuit but it would have shoretened the life of the relay contacts. The fuses could have failed due to a short on the transformer windings or a short in the display unit. I don't think the loss of a phase would have caused either of these faults.
I would be interested in comments from other forum members. If I was working on the fault my next step would be to try just powering the electonics by connecting normal 240 volt mains to the 220 volt input of the transformer. I would fit a 2 amp fuse to the mains plug and wire a 60 or 100 watt filament bulb in series with the mains to limit the current. If this worked it would show that the transformer was OK and the was no short in the electronics.

Les.

I really like that suggestion Les. I will do this test today and post the results.