# Anyone Familiar with the Bridgeport Power Feed circuit board F-6120?



## tfleming (Oct 18, 2017)

Just bought a complete Bridgeport power feed, and I bought it knowing it didn't work.  Seller indicated that it worked up until a week ago, then it smoked out of the control panel and quit.  Well, I got her open today, and here is what I found:

Here is the board:







Here are the reversing switches, notice the one on the "top" is missing a connection in the middle post:






So, here is the "fried" connector, looks like it came loose and "smoked" on the housing:






So, I can certainly put a new connector on it, and place it back on the post.  However, I would like to check a few things out first.  Not sure if it smoked anything on the board when it went to ground.......

Any thoughts or suggestions?  The power light comes on, but neither direction works on the motor.  I get nothing.  No hum, no buzz, NADA (but that is without that terminal connected).  I guess it won't hurt anything to put the wire back on before I try anything.  However, I would think I would get something from the other switch, and it does nothing.


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## Terrywerm (Oct 18, 2017)

I would try a new connector and attach it to the empty post on the switch, but check the rest of it over first. Are there any other empty posts? If not, it's a pretty safe bet that it should connect to that switch. Take a look at the wire length and 'set'. Does the wire seem to have just the right length to attach to that switch and does the wire seem to 'want' to find its own way when connected? I don't know how else to word it, but wires have a tendency to show how how they've been laying for the last umpteen years.


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## tfleming (Oct 18, 2017)

Thanks Terry, yeah, that wire goes there.  I did find the high level wiring schematic for that, and the color code on the "fried" wire is for that post, so I know it goes there.  I am worried what it might have toasted in the circuit board when it hit the case and grounded.  I guess it certainly won't hurt to put a new connector on it and try it.  I can get a new board for it, but that is another $300 (ouch).  If it is something as simple as replacing a specific resistor or capacitor, I am comfortable doing that (if need be).  The circuit board itself, is pretty "old school", so a wee bit of patience with the soldering iron might do the trick!


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## markba633csi (Oct 18, 2017)

If the controller is solid state then a component might be smoked. Are there any fuses in there? Is there a schematic diagram available online?
Mark S.   
ps I can help you troubleshoot it and save some $$


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## tfleming (Oct 18, 2017)




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## tfleming (Oct 18, 2017)

markba633csi said:


> If the controller is solid state then a component might be smoked. Are there any fuses in there? Is there a schematic diagram available online?
> Mark S.
> ps I can help you troubleshoot it and save some $$


Yes, there is a fuse, but it is intact.  However, unknown if the seller replaced that when it first smoked.  I am certainly going to put a new connector on it, and see if it powers up.  From the schematic, the pilot light appears to be at the "front end", so just because that lights when you turn it on doesn't necessarily mean much........and thank you for offering to assist in the diag.


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## tfleming (Oct 18, 2017)

I take it that in the 2nd schematic, the NC and NO are "normally closed" and "normally open" as far as the switches go.  Maybe all this puppy needs is to have that connector back on.  I'll try that here in a bit.  If that works, then "Bob's your uncle"................................if not, then I need to dig a wee bit deeper into this puppy.


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## Keith Foor (Oct 18, 2017)

After reviewing the schematic It looks like that wire is the common power for the directional logic (tells the board which way to spin the motor).  It is off the bottom of the main power feed into the board via a bridge rectifier.  So, if you understand checking diodes with a multimeter, I would look at the bridge rectifier directly off the 115 volt AC input and verify it's not shorted.  
Another way to test this is with a simple inline lightbulb circuit.  Connect a 100 watt light bulb in line of the 115 volt AC input and see if it glows brightly or not when you apply power.  If there is only a faint or no glow, then the rectifier is most likely ok.  If it lights up full brightness then it's most likely shorted.


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## tfleming (Oct 18, 2017)

Thanks Keith, yes, I can check the bridge.  I have a full function multi-meter, so I can also check the DC voltage coming out of the bridge as well.  Not sure I will make it back into the shop tonight, but I will update this thread after testing.


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## markba633csi (Oct 18, 2017)

Hi Fleming, looks like the field supply might be damaged, let me cogitate for a bit and get back to you
Mark S.


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## markba633csi (Oct 18, 2017)

I suspect one of the two field supply diodes might be burned out- D15 or D16.  Check them both.  1N5053 I believe is the number; 2 amp, 800 volt. Should be easy to find a replacement, and cheap. 
Mark S.
ps also check D5 and D6


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## markba633csi (Oct 18, 2017)

1N5408 would be a good sub:
https://www.parts-express.com/1n5408-general-purpose-rectifier-diode-3a-1000v-10-pack--1n5408
You might do even better on the price by shopping around a little-


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## markba633csi (Oct 19, 2017)

Interesting (and probably old) schematic- I've never seen pots (potentiometers or variable resistors) drawn that way. 
A very serviceable circuit, not like new stuff with one big impossible to replace chip that does everything.  
Each and every part in there could be found today. 
Mark


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## tfleming (Oct 19, 2017)

Well, I took another quick look at the board searching for the diode bridge.  I found it, and bridge is comprised of *40HF30* diode rectifiers. They are still available at $9 a pop. Each is rated at 300v and 40A.  It also looks like what "smoked" on the case is not the DC switching wire.  It is one of the 110v ac feeds TO the bridge that is missing a wire nut.  I did not have time to dig out the multi-meter, but I will.  I need to make some time and study this a bit more.  Right now, my theory is, the 110v wire touched the case, and blew the fuse.  The previous owner in his haste to figure out what happened, broke off the DC switching lead, and also put a new fuse in ( looked at the broken connector closely, and there are no carbon or fusion marks, just a clean fracture).  I am making the assumption that the DC switching leads are series, NOT parallel.  If that is the case, all connections must be in place for the motor to work, regardless of direction.  However, those are assumptions, and not based in "advanced schematic digestion".   I am only so-so on electronics, but I know enough to be dangerous.  More to come


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## tfleming (Oct 19, 2017)

Mark, I agree, that is an older schematic.  However, this is an older unit.  I also agree, there is nothing on the board that cannot be replaced.  I figure that with some guidance from folks like you and Keith, I'll have this old girl chooching in no time...... and for less than $300.  Those 40HF30 diodes are HUGE!


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## mksj (Oct 19, 2017)

I would surprised if that diode went, but you can check them with a multi-meter using the diode tester. There are lots of suitable alternatives, you do not need the exact same rectifier, so 40A minimum 300V.
https://www.ebay.com/itm/1N1188A-40A-400V-Standard-Recovery-Diode-5-pcs-/182839422245
https://www.ebay.com/itm/40HF80-40A...ifier-Factory-New-FREE-SHIPPING-/232389030618


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## markba633csi (Oct 19, 2017)

Hi Mr. Fleming, so the wire that arced the terminal was not from the directional switch? I'm a little corn-fused. 
Also, the power bridge has 2 large SCRs in there and 3 of the large diodes.   Can't quite make out the number of the SCRs. 
SCRs are easily checked with a battery and light bulb, if we need to.  Hopefully those 5 parts are OK.
Have you checked/fixed the directional switch wires and tried to power the unit up?  All the directional switch wires must be in place for the motor to run. 
Mark


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## tfleming (Oct 19, 2017)

Mark, first off, just call me Tom.  Secondly, I found a bare connection wire splice for the AC input to the diode bridge, and I am about 90% sure that is what arced to the case.  After closely inspecting the DC switch spade, I did not see evidence of a "short".  Only metal fatigue and a relatively clean break.  No carbon.  However, the AC input splice is just plain NASTY, and I believe that is what arced.  I am going to put things "as they should be" and power it up to see if she chooches.   If there is no joy, then the meter comes out and I go on a diagnostics trip..........


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## markba633csi (Oct 19, 2017)

Tom: Ok yes put all the wires in order and try it out.  If it blows the fuse then we'll grab the meter and get into it.  I haven't lost a patient yet. LOL
Mark S.


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## tfleming (Oct 24, 2017)

Ok, Humpty Dumpty has been put back together again, and no change in condition.....no chooch.....no joy.  Power indicator lights up when power switch is turned on, but other than that, the unit has no life.  Nothing from the JOG button, and nothing when using the FOR/REV shift lever.  I guess I am on to the next step.  I'll have to come up with a way to insulate the circuit board, and power it up while it is not mounted in the unit (and put a ground jumper on it to the case).  Then go component by component and see where the pixies die off.......


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## brino (Oct 24, 2017)

Hi Tom,

Since you have decent drawings, have you done a simple wire-by-wire verification of the connections?

To me it looks like the wiring to those two switches do not match the diagram.
It may be just that I cannot see the colours, or that I'm not 100% sure I can read the "NC" vs. the "NO" contacts, but it's not what I expect.

It should be "low hanging fruit" before you dig too deep into the circuit board.

-brino


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## tfleming (Oct 24, 2017)

Brino thanks for the suggestion.  I did verify the colors and connections.  One of the components must be fried.  Although, I do agree, that it is probably relatively simple.  My plan was to start at the 110v AC connections, and just work my way back with the voltmeter through the AC and DC points.  That should tell me pretty much where the pixies stop.  Where that point is, is probably the toasted component.  Again, I am comfortable with basic electrical blocking and tackling, but I am by no ways an expert.


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## tfleming (Nov 6, 2017)

Ok, I finally got a few hours to myself today, and broke out the Simpson.  What I found so far is that there is 110 AC to the diode bridge.  However, one of the diodes appears to be toast.  I polarity tested all of them with the OHM meter, and found all at 10 ohms +/-3, except for the last one, which measured 2 ohms in both polarities.   Failing diode is circled in blue:







110v AC input is fine.  0v DC output.  So, unless I am missing something, I have a cooked diode.  Basic continuity and voltage testing of the 110v secondary circuit to the transformer was good.    So, I guess I order one of those puppies, and swap the circled one out.  Then continue the testing.  OH, I found the micro-switch wiring was totally reversed as shown on the wiring diagram, so I re-arranged that to match the diagram.  Lastly, I verified the rest of the wiring as per the diagram.


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## markba633csi (Nov 6, 2017)

Tom: you may get goofy readings with the part still in the circuit- unsolder it and test again before you start buying parts- diode should give very high ohm reading in one direction and low (a few hundred ohms or so) in the other.  The two scrs require a battery and light bulb test- maybe later on...
Mark
ps by the way do you know for certain that the motor itself is ok?


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## tfleming (Nov 6, 2017)

Mark, I'll disconnect the suspect one, however I will add that each one did check out with the polarity check except for the last one.  The failing diode had 2 ohm continuity in both polarities, hence my diagnosis.   To be safe though, I'll follow your advice.......


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## chips&more (Nov 6, 2017)

Sorry, but you cannot check that diode in the circuit with certainty. It must be out of the circuit to check with a simple multimeter. There are ways to check in the circuit with more sophisticated equipment however. And I have never seen that diode fail. I would replace those 4 blue colored caps on the center right, whether good or not. And carefully check the board for bad solider joints, smoked component(s) and bad/melted circuit paths. Good Luck…Dave.


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## tfleming (Nov 6, 2017)

One other thing I should point out.  110 vac input to the diode bridge is working.  Output from the bridge is 0 vdc.  That is the other measurement that leads me to believe that diode is toast.  While there still may be more fried components downstream, the bridge is definitely not functioning........I would expect to get some DC voltage reading on the output legs when energized, but alas, no DC Voltage and no joy.......


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## markba633csi (Nov 6, 2017)

Tom: If the scrs are not being triggered you won't have any output from the power bridge.  Also you need field power to the motor.  One step at a time...
Lets zero in on the real problem before you go ordering any replacements
Mark S.


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## tfleming (Nov 7, 2017)

well guys, I made an executive decision, and I bought a new circuit board with some updates to components.  Now, I plan to continue to diag the current board on the thread so I will have a spare.  Time has become very tight for me lately, and while $300 is a moderate chuck of change, I also don't mind investing it.  I have gone through the motor, and it is fine.  The rest of the unit is fine......it all boils down to the board.  I had a couple of discussions with H&W machine repair.  Those guys are top notch.  If you ever need Bridgeport parts, they are a bit pricey, but they are great people.


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## tfleming (Nov 9, 2017)

Great news.  New controller arrived today (2 days after ordering from H W Machinery).  Installed as per instructions, including updated components.  Power feed chooches like a new one (well, almost new, the paint leaves a lot to be desired).  Thanks to everyone.  I am still going to work on the old board to see if I can figure out what is wrong, but for now, the power feed is ready for work!

Thanks again to everyone who responded.


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