Bridgeport 6F mill with Erskine powerfeed control.

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
Dear Sirs,
I have a milling machine where the axis power feeds are non-functional. The main motor works fine (the spindle) but the control board to the power feeds seems to be having some issues? I am hoping that by picking the wise brains of you members I can carry out a simple repair. I have a basic electronic engineering knowledge and can carry out simple repairs but by no means have any advanced electronics background.

1. Firstly the circuit diagram can be seen in image 1 of my attachments. Image 2 is the board in question.

2. In image 3 (top view) and 4 (below view) it appears the cap has blown. I can replace this easily enough by soldering another to the remaining legs once I snip it out?

3. The component with a red button (I believe is a thermal reset-able cut out) does not stay down once pressed taking into account the circuit is out of the machine and on my desk. Can I replace this with a reset-able thermal switch? If so what ratings? I guess this is a fairly old component?

Any feedback here will be greatly appreciated. I am hoping I can get this running again with some simple component replacements.

Thankyou in advance.
 

Attachments

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
I have taken a pic of the top of the board as the one I uploaded was a generic one where I have just noticed further damage. This image is the actual board I am working on. 20180125_102241.jpg
 

LesJones

Joined Jan 8, 2017
2,698
I can't find the suspected thermal cutout (Which is marked "OL1" in the pictures in your first post.) on the schematic. A picture of the etch side of the board may help to identify where it is on the schematic. Have the power feeds ever worked since you have had the machine ? If so did they both fail at the same time ? (I am thinking that you may have lost the 115 volt supply from the transformer in the mill.)

Les.
 

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
Hi Les,
Thankyou for your reply.
The thermal cut out I am referring to (please excuse the probably incorrect use of this term) is the red button on the board surrounded by the black ring. This is marked on the enclosure as 'Reset' so I guess is an overheating protection?
I had not considered the 115v output not functioning? I will meter this when next in the shop. As for the power feeds and coolant ever working for me, no they didn't so I don't know if they went at once?
I have taken a pic of the rear of the board in the hope it helps the diagnosis?
Cheers,
Dave.
 

LesJones

Joined Jan 8, 2017
2,698
I don't think the schematic is for the same board that you have in the pictures. I think you are correct that the red button is a thermal or overcurrent cutout. I have some schematics for different versions of Bridgeport. some show a three phase coolant pump but one shows it to be a single phase motor fed from a 90 volt tap on the transformer so I don't know if the pump not working is related to the table feeds not working. The mark on capacitor C2 looks like something has shorted against it's negative terminal at some time. If you are fault finding be aware that even though there is a transformer to feed the electronics that no point on the electronics is at earth potential. (So DON'T connect an oscilloscope ground to the electronics ground unless you power the feed unit from an isolating transformer with a floating secondary.) I think checking for the 115 volt input to the board would be a good place to start.

Les.
 

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
I don't think the schematic is for the same board that you have in the pictures. I think you are correct that the red button is a thermal or overcurrent cutout. I have some schematics for different versions of Bridgeport. some show a three phase coolant pump but one shows it to be a single phase motor fed from a 90 volt tap on the transformer so I don't know if the pump not working is related to the table feeds not working. The mark on capacitor C2 looks like something has shorted against it's negative terminal at some time. If you are fault finding be aware that even though there is a transformer to feed the electronics that no point on the electronics is at earth potential. (So DON'T connect an oscilloscope ground to the electronics ground unless you power the feed unit from an isolating transformer with a floating secondary.) I think checking for the 115 volt input to the board would be a good place to start.

Les.
Hi Les,
I am sure you are right about the circuit I only found it on Model Engineer forum?
The cap may have shorted due to swarf going into the box? I must admit its quite possible as I used it with the door open stupidly. I will get into the mill tomorrow and check the following:
1. output from the transformer ie 115 volt output
2. the location and type of coolant pump

I wont connect anything to the board and I have no idea how to use a scope so I think I am safe there. In your opinion is the cap a right off? It looks it and I can swop it out. As you suggest this is a good starting point.

Thanks again for you responses it is really helpful to be a member of this type of site.
 

LesJones

Joined Jan 8, 2017
2,698
It is possible that the capacitor has been damaged but it depends on what has been shorted to it. IF we assume that that part of the board is the same as the schematic then C2 is the +15 volt rail reservoir capacitor. From the mark on the board near it it looks like it may have been shorted to the negative end of D2 which could have destroyed the bridge rectifier. If it had shorted to something else then it is more likely that a number of semiconducters would have been damaged. I would expect there to only be two connections used on the cutout and if is not faulty I would expect an almost zero resistance reading between them. There have been a few theads on the Model Engineers forum dealing with Bridgeport problems.

Les.
 

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
In an attempt to get my Bridgeport 6F-powerfeeeds working again I am starting with what looks like the 1st component replacement following checking the motors and brushes. I have identified a blown capacitor. It does not obviously state what value of capacitance it is? I can see its rated at 250v and with a '4u7' do I assume this to be 4uF? Not being very familiar with these parts any clarification on this would be very useful. I have taken 3 pics of the cap in question.20180129_113326.jpg 20180129_113326.jpg 20180129_113319.jpg 20180129_113312.jpg 20180129_113319.jpg
 

LesJones

Joined Jan 8, 2017
2,698
The capacitor is 4.7 uF (It is commom practice to put the decimal multiplier letter in the place where you would expect to see the decimal point on electronic components.) I am not convinced that it is faulty. With faulty electrolytics the insulation at the positive end very often swells or blows out when thay fail. You will pribably find that a modern electrolytic capacitor of the same rating is physicaly smaller. Looking at the suppliers that I normally use and on ebay there are very few axial electrolytic capacitor of that value available. (They are available with radial leads.) There is no reason why you should not use a film capacitor if you can find one that will fit in the space available. (They are normally larger than the equivalent electrolytic and more expensive.)
Did you check if you had the 115 volt AC supply to the board ?

Les.
 

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
Hi Les,
Thankyou for that feedback. I will put in a replacement 4.7uF. I checked the 115v supply and its coming through OK?

So just to confirm I am looking for a 4.7uF cap rated for 250v?

Regards,
David.
 

LesJones

Joined Jan 8, 2017
2,698
That capacitor should work OK if it will fit in the space available. If it was me I would find a way to use a radial lead capacitor an buy it on ebay (As I think Farnell ans RS charge postage on small orders.) I have just looked on ebay and found this axial 4.7 capacitor 450 volts working so this would do. (Any voltage above 250 is ok.) It does not give the physical size in that advert but with a bit more searching you may find one that does give the physical size. I still think that capacitor LOOKS ok but there is no way to know without testing it. It looks likes the leads have been cut of you would have to replace it even if it was ok.

Les.
 

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
Hi Les,
The cap that I ordered has arrived and I am ready to solder it in place. Excuse my electrical ignorance but which is the + side? The is no marking on it other than the voltage and makers name. Do I assume its the left side when viewed from the side with the voltage printed on it?

Also I have checked the diodes as you have suggested that make up the rectifier. They are conducting both ways so I assume these are also blown and need replacing?

I can order these if you think its worthwhile?
Cheers,
Dave.
 

LesJones

Joined Jan 8, 2017
2,698
If its the on in the link to RS's website in post #16 it does not matter which way round it goes. My comment about the bridge rectifier were made when I thought the suspect capacitor was C2 (It looks like it is marked C2 on the picture of the board.) It can't be in the position of C2 on the schematic as it is the wrong value and voltage rating. I have no idea what the 3 diodes near the capacitor do. The only real way to fault find is to start by tracing out the schematic of the board. (Which will take a long time.) If you are just testing components without knowing where they are in a circuit you will need to disconnect one end as the circuit around them could confuse the readings.

Les.
 

Thread Starter

Abmeboy

Joined Jan 25, 2018
13
I can confirm that the cap is C2.
I will go ahead and put in the new cap and see what if anything works following this. I agree just putting on the meter to the diodes in place isn't a great help. I realise this now.
I will feedback my results.
Thankyou again for the information.
 
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