Strippit  and  General Electric
Servo PWMC Comp Values
In 1970's and 1980's,  before  Neutron Jack  Destroyed  The  U.S. CNC Control Industry,
General Electric Co. was the World Leader in CNC Controls and Servo Drives.

These CNC Control & Servo Systems were Widely Used on Hundreds of Different Models of 
Lathes,  Mills,  Machining Centers,  and of Course,  Strippit Turret Punch Machines.  
G.E.  Hi-Ack Model 2 and 3 Servo Drives Provided the Power for Machine Axis Motion Control.

CNC Machines had Great Variations in  Axis Speeds,  Weight,  and  Rigidity.   To Provide Machine Designers
a way to Compensate for these Variations,  G.E. Provided on  All  PWMC Servo Control Boards Terminals
where Machine Designers Selected and Installed Unique Values of Several  Resistors,  Capacitors,  and 
Zener Diodes as a way to Taylor Servo Response of Each Individual Axis for each Type and Model Machine.

This Important Comp Value Information should be Provided in  Original  Machine Manufactures
Schematics and Service Manuals,  and  Copies of these Important and Unique Comps for Each Axis
should be  Carefully Copied  and  Preserved!

Unfortunately,  Like  Egyptian Hieroglyphics,  the Knowledge that  All  PWMC Boards
Have to be Properly Configured with Correct Compensation Values,  and more Importantly 
What these Values Should be for Each Individual Axis on Each Machine,   is  Rapidly becoming Lost!

If  Wrong Comp Values are Installed on  PWMC Board,  or  "Double"  Comp Values Installed, 
the Machine Axis will  Position Poorly,  Over-Shoot,  Oscillate,  or  Not Position and Run at all.
Damage to  Power-Boards,  Power-Modules,  and  Servo-Motors could also result.

When  G.E. Built these Boards, 
G.E.  Installed a  Standard TEST-Set of Comp Valves  Just for their Testing Procedures.
TEST Comp Component Values will  NOT  likely be Correct  for  Most Axis on Most Machines,
and  usually will Need to Be Changed  Per The Original Machine Manufacturers Specifications!

As I Sell and Repair PWMC Servo Boards,  I am Finding Same Problems Over and Over Again
caused by Uninformed Technicians and Servicemen making Mistakes at their Shops and Factories.

  1  --  Swapping  PWMC Boards  (Without Changing the Comp Values!)  Between  Different Machine Axis, 
          or  even Worse,  Between  Different Machines,  Causing Multiple Problems on Multiple Axis and
          Perhaps Losing what the  Correct Comp Values Are  for  All Axis on their Machines.

  2  --  Installing a New or Repaired Board from a Test Facility that has Test-Comp Values Installed,
          but  Not the Correct Comps for this Particular Machine and Axis.

  3  --  Installing Incorrect Comp Values for a Particular Machine and Particular Axis,  by Perhaps,  Copying
          Wrong Comp Values from Old Board and Installing  the Same Wrong Comp Values on  New Board.

  4  --  Installing New Comp Values  Without Removing  All  Old Test Comp Values so that you
          now  have  "Double"  or   2  Sets of Comp Values Installed!

If you are having Servo Problems with  G.E.  Hi-Ack  Model 2  and  Model 3  Servo Drives,
I would Always Check that  Comp Values are Correct  on  Each-Axis  for this  Particular-Machine!

General Electric  Model 2  PWMC3
  and  Model 2UL  PWMC4  Boards
PWMC3  Series was the First Type of  Model 2 Servo Control Boards.
First Version was  PWMC3,  but  Boards were Continuously Improved over the Years  into  Newer
PWMC3B,   PWMC3C,   PWMC3D,   PWMC3E,   PWMCF,  and  Final Version   PWMC3G.

These Boards had 10 Screw-Terminals  (Except for  PWMC3F  which has  10 Solder-Posts)  where 
G.E. Test Comp Values  or  Customer's Machine Comp Values were Installed,  as  Shown in Photos Below.

PWMC3  Servo Control Board Type
10 Screw-Terminals  for  Comp Values.

Boards has  2  Connectors  5PL  and  6PL.

PWMC3D,   PWMC3E,   and   PWMC3G.

There Photos are Not showing
Complete Circuit Boards,
but  are Emphasizing the
Comp Parts Installation Area.
PWMC3F  had  10 Solder-Posts  for Comp Values.

This was the  First  "U.L." 
(Underwriters Laboratories)  Type Board
Developed for Increased Safety and Reliability.    PWMC3F  has a   3rd  Connector  16PL
where  Board Received  D.C. Power.
U.L. Boards  went into a   U.L. Servo Chassis.

G.E.  Eventually Redesigned  All Boards  and Chassis  into  New  U.L. Types,  But
PWMC3F  and   New  U.L.  PWMC4  Boards were Virtually Identical and were simply Rehashed
Old  PWMC3E  Boards.

This Board could also be Used in Older
Non-U.L. Chassis by  Soldering  4 Jumper Wires Across  8 Solder-Posts  like  Photo at Right.
Board would then get it's  D.C. Power  from
5PL  and  6PL  like other Boards in the Series.
PWMC3 Series Boards  Left  the  G.E. Factory with  Standard Test Comp Values Installed.
These Values were;      R1   2.2 M Ohm,       R2   47K Ohm,       R3   10 Ohm,       C5   .47MFD  Capacitor.

PWMC4  UL Series Boards  Left the G.E. Factory with Slightly Different Test Comp Values Installed.
These Values were;      R1   2.2 M Ohm,       R2   68K Ohm,       R3   10 Ohm,       C5   .47MFD  Capacitor.

At  The Strippit Company,  These Test Comps were  Engineered and Changed  to  Provide
Optimum Servo Drive Response  for  Each Axis  on these  High-Performance CNC Turret Punch Machines.
Following are a List of Comp Value Components  used by  Strippit on  Machines with Model 2 Drives.

Machine Type               X-Axis                                     Y-Axis                                                     T-Axis
                                           R2      R3     C5    RL   CL    R2      R3     C5     RL   CL     Diode         R2      R3     C5    Diode
FC750  &  FC750/2  100K  100K   .22    --      --    100K   47K    .27     --      --         --              --        --        --        --

FC1000/1  30S/3             100K   47K    .22    --      --    100K   47K    .27     --      --         --             100K   47K   .33  1N5231  5.1V
FC1000/1  HC         100K   47K    .33    --      --    100K   47K    .27     --       --        --             100K   47K   1.0  1N5231  5.1V
FC1000/1  "A" Rev. D     100K   47K    .33    --      --    100K   47K    .27     --       --        --             100K  100K  1.0  1N5231  5.1V
FC1000/1  "A" Rev. F     100K  100K   .22    --      --    100K  100K   .27      --      --         --             100K  100K  .33       --

FC1000/2  HECC80/1      100K   47K    .22    --      --    100K   47K    .27   330   .022       --            100K   47K   .33       --

FC1250  51S/4  Y Size3  100K   47K   .27     --      --    100K   47K    .47     --      --         --             100K   47K   1.0       --
FC1250  "A"     Y Size4  100K   47K   .27     --      --    100K   47K    .47     --      --   1N5231 5.1V  100K   47K   1.0      --
FC1250  "A"     Y Size5  100K   47K   .27     --      --    100K   47K    .47     --      --   1N753B 6.2V  100K   47K   1.0       --

FC1250  HECC80/1        100K   47K    .27    --      --    100K   47K    .47  (330)  (.1)  1N753B 6.2V  100K  47K   1.0       --

FC1250/30/1500 H80/1    100K   47K    .1      --      --    100K   47K    .33     --      --   1N753B 6.2V  100K   47K  .33  1N5231  5.1V
   "  H80/1 33-ST. Laser   100K   56K    .1      --      --    100K   56K    .33     --      --    No Diode?    100K   75K  .33   NO DIODE
   "   H80/306 33-ST.         100K   47K    .1      --      --    100K   47K    .33     --      --    No Diode?    100K   47K  .33   NO DIODE

FC1500/45      (D.R.)        68K  100K   .33   220    .1     50K   31K     .27  (330)  (.022)     --             100K   47K  .33  (RL330  CL.022)
FC1500/45        2nd       100K  100K   .33   220    .1

  ---  Zener-Diodes Provide Current Limiting to Protect Servo Drive and Servo Motor,
       lower Zener Voltage means lower Current
  ---  RL  and  CL  Parts  Provide  High-Frequency Attenuation 
       so that Axis does  Not Oscillate and "Buzz".
  ---  RL  and  CL  Parts,  In  Brackets,  I added to  Problem Machines to  Cure High-Frequency Oscillation
       so that Axis does Not Oscillate and "Buzz".   The Point is that some Comps may Need to be Adjusted
       for some Machine's Axis to Run OK.
  ---  At Strippit Co.,  we Left the  R1  2.2M Ohm Resistor  on  All  PWMC Boards, 
       Removed  Other  G.E.  Comps Parts,  then  Added Proper Comp Values for Machine
       and  Axis  Per Chart Above.   Chart  Values Shown Just as an Example!

PWMC7  and  PWMC8  Boards leave the
G.E. Factory with  7 Screw-Terminals, 
with  All Screw-Terminals  Left Empty.

The G.E. Test Comp Parts were Soldered Directly to Circuit Board,  so this made it
Very Easy for the Uninformed to Add our Strippit Machine Comps to Screw-Terminals,  and now you have  "DoubleComp Parts
on Board and your Machine would Not Run!
This is  A Very Common Problem!!!

At Strippit,  we Left-On  R10  2.2M Ohm  and  C8  .1MFD,   but  Carefully  Cut-Off 
R9,   R11,   R17,   and   C7,   then Added Our Replacement   R9,   R11,   R17,   and   C7
Comp Values  to  Proper Screw-Terminals.

On Strippit FC1000/3 Machines Servo was Mounted on Punch Machine Frame and was Subject to Much Vibration.   So,  Instead of Using Screws,  we Removed Screw & Nut from Terminals,  and  Soldered Our Comp Values Directly to Terminals for a Very
Secure Connection,  like in Photo at Right.
G.E.  Hi-Ack Model 3  and  3A  Servo Drives were Designed to be a  Higher-Voltage  (150 Volt .D.C.)
and  Higher Performance Servo Drive than the Older  Model 2  (90 Volt D.C.)  Servo Drive System.

Early  Model 3 Drives used a  PWMC5  Board  to Drive  2 Power-Modules
and  PWMC6  Board  to Drive  4 Power-Modules  for  Higher-Current Capacity.

The Original Model 3 Drive was Not Reliable,   so  G.E. Engineers  Redesigned
All Circuit Boards  and  Servo Chassis  in to  Much Improved  Model 3A  Servo Drive.

PWMC5  Board  was Replaced by Improved  PWMC7 Board.
PWMC6  Board  was Replaced by Improved  PWMC8 Board.
If you still have an  Old  PWMC5  or  PWMC6  Board  in your  Model 3 Drive,
Throw It Away  and  Replace it with  Improved   PWMC7  or  PWMC8  Board!!!

Early  U.L.  PWMC3F  and  PWMC4  Boards
were  Redesigned into
PWMC4A  and  PWMC4B  Servo Control Boards.

PWMC4A  and  PWMC4B  Boards were Very
Cleverly Redesigned to be Backwards Compatible with  All  U.L.   and   Non-U.L.  Chassis,
did Not Need  or  Have the 8 Solder-Posts,
and used   8 Screw-Terminals for the Same
Comp Values  that used  10 Screw-Terminals
in older PWMC3 Boards.

So if Replacing a PWMC3 Board with a Newer PWMC4A  or  PWMC4B Board,  do NOT use same Screw-Terminal Numbers  as they have Changed.   Instead,  Use Comp Value  Part Number Printed
on the Board.    Example,  on
PWMC3  Boards  R3 goes Between T5  and  T6,  But  on 
PWMC4A  Boards  R3 goes Between T5  and  T1.
PWMC7  and  PWMC8   Boards
are  Very Similar, 

PWMC7  Board Drives  2 Power-Modules

and the

PWMC8  Board Drives  4 Power-Modules
for  Higher Current Requirements.

General Electric  Model 3  and  Model 3A
PWMC7  and  PWMC8  Boards

PWMC7  and  PWMC8 Boards  Left   G.E. Factory  with  Standard Test Comp Values  Installed.
These Values were;     R1   2.2M Ohm,      R9   47K Ohm,      R11  1K Ohm,      R17   10 Ohm,
C7   .68MFD Capacitor,      C8   .1MFD Capacitor.

For Strippit  FC1000/3  and  FC1500/45  Machines,  we Left-On  R1  and  C8,  
Cut-Off    R9,    R11,    R17,   and   C7
then  Added New Comp Value Parts Per the Chart Below.

  Machine             X-AXIS                                             Y-AXIS                                              T-Axis
                              R9       R11       R17      C7             R9       R11       R17      C7              R9       R11       R17       C7

  FC1000/3          120K   220       120K    .27 UF      120K   220       120K    .27 UF       120K   220       75K      1.0 UF

  FC1500/45        120K   220       120K    .27 UF      120K   220       120K    .27 UF       120K   220       75K      1.0 UF

Monarch Machining Centers,  Gidding & Lewis Horizontal Mills,  and  Warner & Swasey CNC Lathes  are
the only other Manufacturers I have seen,  Beside Strippit,  that also used Model 3 & 3A Type Servo Drives.
As Most of these Old machine Tool Companies are now out of Business,  Try to Find
Original Comp Values  for your Machine  in Your  Schematics and Service manuals!

If your,  Non Strippit,  Machine Axis is Not Positioning Well,  and Original Comp Values have been "Lost",
Try to get them from Machine Original Manufacturer!

If Not Available,  a Smart Technician  or  Engineer will  NEED  to
Read Set-Up Information in  Correct G.E. Servo Manual  and  Experiment to  Find Values that will
Allow  Smooth Acceleration and Deceleration of Axis  with  No Overshoot  or  Oscillation.
You can use G.E. Test Comp Values as a Starting Point,  and use Strippit Machine Values as Real-World Examples Selected by  Real Electronics Engineers.    On Strippit's,  X  Values were for Light  X  Axis,  and
Y  Values were Selected for Heavy  Y  Axis.   Adjust Valves Carefully until you achieve Performance you need.

I have Worked on some of these Other Brand Machines,  and have been  Amazed at how Poorly Servo
System was Integrated with  Poorly Chosen Comp Values on  PWMC Boards,  and  Improper Handling of
Servo Inhibits and Contactors.   It's hard to Explain to Customer that His Machine was  Poorly Engineered
and That's why they have Problems,  But  I get the Retort   "Well,  it's Run Pretty Much OK for 30 Years".

I have come to  Really Appreciate  what  Good Engineering  was done at Strippit,   in  The Old Days.
Nowadays,   with  Most  Real Engineers   having   Left StrippitNot So Much......

We have Small Stock of 
G.E. Hi-Ack Servo Drive Manuals For-Sale
if you have Lost Yours.

These come in  4 Types;
---   Model  2   
  ---   Model  2 UL
---   Model  3   
---   Model  3A 

You and Your Serviceman
Cannot Work  on
Your Machine's Servo Drives
Without The Correct Manual!
This page was last updated: February 7, 2023
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