Watlow 96 / 97 controllers repair and upgrade

by Updated: Nov 11, 2020diy-miscellaneous0 comments

Avi’s projects that make use of Watlow controllers:

Rancilio Silvia Mega-Mod
Rancilio Rocky Timer-Mod

Watlow controller repair

The secrets of Watlow 96/97 controllers…

Watlow series 96 temperature controller is a 1/16 DIN panel mount dual display dual set-point controller which offers many advanced functions.
It is tailored to perform hardware and software needs with modules that are pluggable and exchangeable and software menus that can be programmed to fit exact application requirements.
Watlow series 96 temperature controller ideally suited for applications in markets such as plastics packaging, semiconductor, food processing, and lab equipment.
This controller offers one universal input, a second auxiliary input, and four outputs.
Programmable functions can be Temperature measurement, Heating, Boost heating, Cooling, Alarms, Digital communications, Retransmit.
With its fast 10 Hz sampling, variable time base burst firing outputs, 0.1 percent calibration accuracy, the Watlow Series 96 temperature controller can handle some of the toughest application needs.
Watlow series 97 is 1/16 DIN panel mount over-temperature, limit controller with user defined messages.
It is microprocessor-based controller with a single input, second auxiliary input and four outputs.
Input one is used to measure temperature from a sensor. Input two can be utilized as a remote reset switch or a hardware lockout switch.
With up to four outputs, the controller is versatile in handling applications that require a high/low limit, alarms, retransmit and communications.
The series 97 limit controller is added to thermal applications to limit over-temperature conditions.
The series 97 limit controller provides safety assurance against instances where a high temperature runaway condition could occur from a shorted input sensor or an output device that could fail in a loosed position.
It is recommended for any application where thermal runaway could result in large product scrap costs, affect operator safety, cause damage to equipment or create a fire hazard.
96 and 97 controllers has the same design, the same external housing and panel mounting accessories.

While modding my Rancilio Silvia coffee machine, I needed to replace a defective Watlow 96 series controller.
I first started to look for a repair lab when I have found that Watlow 96 series is a modular system in which its output modules are exchangeable.
This means that its modules can be replaced, added or removed in order to repair or create a new controller model.

Problem is that the 96 controller series is obsolete and you can’t order a replacement part.
If you need a replacement part, you have to find another working controller and take out the module that you need to repair your fault one.
While this is easily done, one should note that each output module has its specific location requirement that should be followed in order to end with a working controller.
Another important information that I have found is that both 96 series and 97 series share the same modules.
This helps a lot and increases the possible inventory to look for in order to acquire a controller that its modules can be used for the fix.

In this guide I’ll show you how to replace / add /remove a module of this controller, fix or create a new controller model.

DISCLAIMER – Important!

Before we begin, please review the following tables that show all possible module combinations of the 96 and 97 series.

 Tip: Use a new module only according to the location specified in the tables.

 Tip: Replacing / adding / removing of a module might erase your controller settings.
It is therefore advised to record all your controller settings prior of starting this procedure.
1. Disconnect power from the controller to allow its disassembly.

2. Remove all terminal blocks connected to the rear of the controller.

 Tip: Start with the power terminal block connected to pins 8+9

3. Remove the controller from the machine panel.
You do it by unscrewing the long screws of the square frame few turns first.

Then pressing the screws heads down in order to release the frame’s snaps from the slots and follow with sliding the rear frame towards rear and removing it from the controller.

Now you can slide out the second frame and slide the controller out of its mounted panel.

4. Disassemble the case.
Tip: It is recommended to ground yourself and your working place with proper ESD protection before you start disassembling.

Insert a small screwdriver into the slot on the top of the case and gently twist the screwdriver to separate the case halves.
Repeat the above on the bottom of the case.
Separate the case halves by moving it perpendicular to the front panel
Gently slide out the circuit boards sub-assembly

5. Disassemble the circuit boards sub-assembly
Gently pull the two large circuit boards apart. (perpendicular to it)
Tip: Note the small tabs and tabs guide holes of each board you disassemble.

 Tip: There are 2 types of main boards sub-assembly, one that its connector is on main board 1 and the other that its connector is on main board 2. This does not change anything in the process. See images of the 2 types.

6. Identify the module type and its slot that you’re about to replace / add / remove.

 Tip: Make use of the data in the tables above to determine correct type and location.

 Tip: Slot numbers (1,2,3,4) appear on the large circuit board next to each slot.

7. Replace / add / remove the specific module you need to change.
In case you replace / add a module, make sure you attach the module correctly with all pins engaging properly.
 Tip: Module identifier (DCSW, MRLY, MR3, PROC, SSR, RS232, COMM) appears on the back of each module.
Be certain you identify the module board correctly.

 Tip: Module type F (PROC) and module type M (PROC) are actually the same module.

 Tip: Module type F (PROC) is prohibited in Series 97.

 Tip: Module type D (MRLY) is mandatory in Series 97 in output #1.

* Image of type R – RS232 – P/N Z100-0739-0007  contributed by Burcham’s Surplus
8. Reassemble the printed circuit boards.

 Tip: Match the module tabs and the main board guide holes as you reassemble.

 Tip: Look at the boards from the back to make certain all the output boards are straight and perpendicular to main boards.

9. Reassemble the case.

  1. Insert the circuit boards sub-assembly into the back half of the case with long pins connecting the two main boards facing upwards.
  2. Insert the boards and the rear case into the front half of the case making sure main boards meets the case slides and that the 4 small arrows on the top align.
  3. Make sure the 10 pins on the front of the sub-assembly meet the display board socket that is inside the front of the case.
  4. Case halves should snap together freely when you reach the end of the way.

 Tip: If applicable, remove relevant knockout parts from back cover prior of reassembling.

 Tip: If applicable, add clip cover to relevant empty hole in back cover.

 Tip: If applicable, replace / add relevant terminal blocks according to your new configuration.

10. Update label
If applicable, update unit’s model number and wiring information of left side label.

 Tip: You can use data from the tables above.

 Tip: Label external dimensions are: x=37.5mm, y=35.5mm

11.Verify wiring
In case you replaced a module with another module type and/or added / removed a module, verify that all wirings to terminal blocks are correct.

 Tip: If needed, get help from the 96 user’s manual or from 97 user’s manual.

12. Re-install the controller

  1. Slide the controller through the panel opening.
  2. Slide the 2 back frames from behind.
  3. Make sure rear frame snaps are locked into position and tighten the screws to firmly hold the controller to the panel.
    Don’t use excessive force.
  4. Insert all terminal blocks to their relevant position in the controller.
13. Test and operate the controller.

  1. Upon first power up, ERR10 message might appear. In such event, turn the power off.
  2. Power up again the controller and this will clear the error message.
  3. If necessary, reprogram the controller to its former / new settings as required.
Voilà, you have completed the repair / upgrade of your Watlow 96/97 controller.



Buy Silvia Mega-Mod banner with link to Buy page
Buy Silvia Mega-Mod banner with link to Buy page

Avi’s projects that make use of Watlow controllers:

Rancilio Silvia Mega-Mod
Rancilio Rocky Timer-Mod

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electric hazard sign


1. Watlow controllers runs on high voltage.

Any modification made to your Watlow controller may cause damage to your equipment and harm to yourself or to others. 
Any modification made to your Watlow controller will void manufacturer warranty.
None of the following mods is recommended by me nor by the manufacturer, Watlow. 
These pages show only my personal experience and know-how.
If you follow any of the mods, you do it on your own risk and responsibility.

2. Copyright © 2011 Avi. All rights reserved. 

Content including all text and images in part or in whole may not be reproduced, retransmitted, stored, distributed, disseminated, sold, published, broadcast or circulated in any medium
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