bridgeport HELP PLEASE!!

Mar 13, 2008 17 Replies

Hi Friends,



I'm trying to help my Italian friend sort out an electrical problem with his Bridgeport mill.



Please excuse my inexpertise in electrical terminology. I am just a friend trying to help him



out as he doesn't speak english and there is no Bridgeport support here in Italy. This is



what I know about his situation:


  1. He has a "burned" resistor (I think that's the right term) on his "FEED CONTROL" circuit

board. It blew and there is a heat marking on the board where it was fried.


  1. The resistor is marked R6 on the board, which corresponds to the wiring diagram.


  1. The photos illustrated show the basic type of mill (Bridgeport 2HP model), the electrical



panel, the position of the electrical board for the feed control, the position of the board,



and the general electrical layout.


  1. The mill was manufactured in 1979 and the serial number is 7978.

The resistor was burned and there is no visible markings or colors with which to reference.



He is asking me if anyone knows what the resistance capacity is (in ohms??) so he can



source a new one.



Can anybody help two lost souls? Sorry again that I'm not a machinist or electrician.



Thanks so much for reading and we'd really appreciate your help.



Ciao, darren


There must be some other problem that caused the resistor to burn up. So just finding the value and replacing it won't be a solution. I don't have a schematic here to check but may have at school, I won't be able to check till Monday if this thread hasen't solved your problem by then I'll giv it a look. ...lew...

R6 shows as 47 Megaohms on my schematic.

cheers T.Alan

22 Megohm is the highest standard value. Anything higher is either special order, or made from a group of lower values.

milliohms maybe? Best regards, Spehro Pefhany

What ever the value - make a set up to be one if need be.

If you want a large value - Rtotol = R1+R2+R3..... when in series.

-/\/\--/\/\-/\/\-....

If the value is small - you can parallel them together for a smaller one.

so all ends are together on one side and the other side all ends together. Make a pigtail if needed - but they become series resistors then - the leads.

If you want to make a 47 millohm - sounds like a sense resistor.

If this is a tube circuit - it would be k or meg for most -

It would be best to tell us the circuit that that part is in. And where.

Transistor / triac / tube - and where the part is .

Low values can be made from large fuses that are trimmed down to increase value.

Martin

Mart> >

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You could plug a 47 Meg Ohm resistor into the wall socket all day and it would never burn up, even on the 230 V European mains. So, the 47 MOhm value must be from a different circuit assembly than the original poster has. (Might also be 4.7 MOhm.) I'm guessing this is a manual mill with a power feed with a variable-speed control on a DC motor. I think Bridgeport did make one of these under their own label, but a real pupular one is the "Servo" brand, too. So, maybe we need to be sure we know the brand of the power feed unit.

Jon

Or even .47 Megohm, if the person doing the drawing didn't know the difference.

A 47 meg custom resistor would cost 10 or more times the cost of two

22 meg and a 3 meg resistor 47 and 66 Meg were used in early color TVs in the focus circuit. They cost about $5 wholesale, and half watt 5% resistors were a few cents each. The only reason the custom parts were used was the high voltage would break down the housing and arc over or set it on fire.

Hi Fellas,

Looks like an interesting conversation. I wish I knew what you were talking about so I could help out. Tomorrow I will ask the owner of the mill what the brand name of the power feel unit is so I can offer up more info. Is there any other pertinent information that I can forward to help with the discussion?

I sincerely appreciate all the dialog and interest in resolving this problem.

Thanks,

Darren

My bad, it is 4.7 MOhms . Bad eyes, did not see the period between the numbers. R6 is between a transistor Q1 colector and a 741 opamp with a

22K before it and a 100K after it.

Q1 likely shorted?

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the s*it out of you for torturing the cat." Gunner

A missed period has been know to cause large problems. Gerry :-)} London, Canada

Gerald Miller wrote:fter it.

Yep: That reminds me of the joke about the little boy in grade school and the "most important word you can think of". The kid said " period " the teacher wondered how. The kid said the parents raised such a fuss when his sister missed one. Or something like that, I cant tell jokes without messing them up. :-) ...lew...

On Sun, 16 Mar 2008 17:32:00 -0400, with neither quill nor qualm, Gerald Miller quickly quoth:

1 missed period = 1 pregnant pause.

-- Death is more universal than life; everyone dies but not everyone lives. -- A. Sachs

4.7 meg ohms - is it 1/10 watt? remember power = voltage squared / resistance - I doubt that unless you have some very high voltages in there (to get a tenth watt, you need about 685 volts if I didn't slip a decimal) - suggest you look more carefully at the board - it may be a different resistor

Hi Folks,

More info taken directly from the circuit board (posterior side stamped in gold character text):

PD71114/01/B - ISSUE 8 (OR B)

Printed on the black dust cover which shrouds the circuit board is marked: ERSKINE SYSTEMS LTD SCARBOROUGH YORKSHIRE

ELY 28.023 EM

80.42

Does this create any clarity or add to the confusion??

Thanks for the ongoing support.

darren

Well I doubt the schematic I have access to will be any help since it is a US drive. I forgot to look today. :-( sorry. ...lew...

And with that, often manufacturers used wattages that were thousands of times needed (and no harm) simply to make it possible to manufacture.

Often space limits the size but simply more or equal to the wattage is required.

Martin

Mart> 4.7 meg ohms - is it 1/10 watt? remember power = voltage squared /

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