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Power Feed on Bridgeport not working.

Power Feed on Bridgeport not working.

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Chris Pocock04/07/2019 12:41:11
9 forum posts


Our powerfeed on the X axis of our Bridgeport isn't working.

There is a 110v supply to the Erskine unit, which reads ok, although the transformer was pretty hot this morning. No idea what it's normal temperature is.

The potentioneter goes from 0-50k ohms as if it is new.

The fast travel button shorts out the pot, as expected.

Both microswitches have been tested at the crimps just below the mircoswitches, both has 1x NO & 1x NC contacts, all good. When connected back up, they seem to switch polatity as they should.

All cables have been tested end to end, and between each other. All good.

Motor armature and field have resistances that you'd expect (I've forgotten readings!).

Reset button in Erskine unit has been pressed possibly a hundreds times!

When powered on (switch for powerfeed on, main on button pressed & direction selected via lever connected to microswitches), there is no voltage to microswitches from Erskine unit, nor any voltage to armature or field.

Any advice please?

I'm presuming it's a new Erskine unit needed?

Chris Pocock04/07/2019 12:44:51
9 forum posts

Emgee04/07/2019 15:13:06
1535 forum posts
219 photos

Hi Chris, check with a meter that the Reset is closed.

Test all components on the heat sinks, they are likely candidates for failure, especially if the axis has been jammed.


Chris Pocock04/07/2019 15:22:42
9 forum posts

Hi, will do.

It stopped as it was traveling at a slow speed with quite a small cut.


Edited By Chris Pocock on 04/07/2019 15:22:52

Clive Foster04/07/2019 15:35:31
2245 forum posts
73 photos


Do you have circuit diagrams? PM me if you need them as I did a nice data set including a typical circuit for the Bridgeport group on Yahoo which has now moved to

Alternatively Sorted Machine Sales offer a service exchange unit for £109, presumably + VAT and postage. **LINK**

Its a pretty straight forward unit so anyone up to speed on controllers of that era should be able to fix it. Ought to be less costly than the exchange service but more hassle. DIY is likely to have issues with finding components as some are well obsolete even for a relatively modern one like yours.


Edited By Clive Foster on 04/07/2019 15:36:10

David George 104/07/2019 19:03:13
1254 forum posts
438 photos

Have you checked the carbon brushes as they are the first things to give a trouble and secondly the cables have a tendency to break inside the insulation as I have found out in the past. Check each cable end to end and move the cables about.


Les Jones 104/07/2019 20:09:06
2134 forum posts
146 photos

Here is a link to a post on another forum that is related to an Erskine power feed. It contains a schematic which should help tracing the problem. You may have to join the forum to view all of the information. If that is the case let me know and I will post the schematic here.


Chris Pocock05/07/2019 08:38:38
9 forum posts


We have had problems with the cables before. All cables have been tested end to end and between cables (to test if they have become damaged and connected inside the conduit).

Brushes are fine, replaced a few months ago I believe.

Chris Pocock05/07/2019 08:41:04
9 forum posts
Posted by Les Jones 1 on 04/07/2019 20:09:06:

Here is a link to a post on another forum that is related to an Erskine power feed. It contains a schematic which should help tracing the problem. You may have to join the forum to view all of the information. If that is the case let me know and I will post the schematic here.


Thanks, I'll have a look later when the important jobs are done!

Les Jones 105/07/2019 10:12:11
2134 forum posts
146 photos

Here is the schematic.

Erskine power feed schematic.jpg


Clive Foster05/07/2019 10:50:05
2245 forum posts
73 photos


Do you know what breed of power feed controller that circuit schematic is actually for.

Looks to be the official Bridgeport one for the 8F series power feed with the board co-located with the controls in a box fixed to the motor mount. Also found labelled as the 12 wire version via internet searches. Unfortunately I don't have good enough pictures to be sure.

It's not a Erskine and I think not the later similar but slightly different version made by Quinton Crane as it has 741 op-amps on the board. The pukka Erskine units are all discrete components. The Quantum has, I think, one 14 or 16 pin IC package on the board which could be a dual op amp but somehow that circuit doesn't quite look right.

That said its half a decade since I had the cover off the Quinton Crane unit I had re-furbished as a spare for my Erskine one so memory may be wrong.


Chris Pocock05/07/2019 11:15:26
9 forum posts

Just a quick reply, as I'm still working on other breakdowns:

There seems to be 2 types of Erskine, or at least I have found two wiring diagrams wichi show completely different wiring to the connections.

Clive Foster05/07/2019 13:28:04
2245 forum posts
73 photos


Pretty much all the Erskine and Quinton Crane power feed controllers use the same output connections via the same multi-tag strip. As mentioned above they are all pretty much the same circuit too.

There is an early obscure and rare Erskine variant with a smaller board and different circuit about which I have no information which may use a different output connection set-up.

Yours is a standard Erskine variant. I do have set-up information, some test data and a typical circuit, most of the changes between builds are active component type numbers not major functional variations.

Confirmed that the diagram from Les is for the American 6F & 8F power-feeds having the board colocated with the motor. My copy of the Hardinge produced Bridgeport Manual M-450, revised August 2005 has full details on that one.


Edited By Clive Foster on 05/07/2019 13:28:30

Chris Pocock12/07/2019 07:55:47
9 forum posts

Thanks for the advice.

I've sent it away to an exchange company as I didn't have a lot of time to look at it.

Nothing noticable on the board, no damaged tracks, no popped capacitors, no burnt resistors.


Chris Pocock15/07/2019 15:35:40
9 forum posts

For future reference there should be a short across the field winding (pins 4 & 5 on the Erskine) when the lever is in the mid-position (stop).

Clive Foster15/07/2019 19:36:52
2245 forum posts
73 photos

Quick clarification to the post above from Chris about the Erskine power-feed controls on Bridgeport 6F and 8F machines.

The short across the field winding when the lever is in mid-position (stop) is on the control switch side not on the board.

Obvious if you have the wiring diagram, or at least the Erskine connection and set-up data, to hand but potentially confusing if you are probing around with the board still connected.


Roger Audet26/03/2020 17:35:32
1 forum posts

Hi Chris and Clive,

I am looking to fix a board similar to the one Chris posted the pictures for. Most of the parts are identifiable but R6 is burnt to the point where I am unable to know what the specs are for that resistor.

Could one of you be kind and supply this information so I can order the replacement?

By the way the board I have is a PD-1114-03-B rev 3 if that is important for determining the value of R6.



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