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  • Rational cpc 201 heating element problem

     fixbear updated 3 years, 6 months ago 1 Member · 21 Posts
  • guest

    January 18, 2017 at 12:00 am

    Hi, I’m in hands with a Rational cpc201. The heating elements won’t kick in as they should. Fans and display starts as normal after turning the unit on. I see that the on / off switch is missing a connection, does anyone know where this is supposed to be connected? Part number for plug/cable would have also been very helpful. Thank you.


  • ectofix

    January 18, 2017 at 7:46 pm

    vtech wrote:


    Hi, I’m in hands with a Rational cpc201. The heating elements won’t kick in as they should. Fans and display starts as normal after turning the unit on. I see that the on / off switch is missing a connection, does anyone know where this is supposed to be connected? Part number for plug/cable would have also been very helpful. Thank you.




    CPCs?  I maintain five of them.


    The pictures were helpful. A SERIAL NUMBER would’ve been nice too.


    The CPC ovens went through MANY changes from 1997 until 2004.  From looking at your pictures, your oven was made prior to 10/99 (No IQT controls).  So..probably an original version “A” oven (there were four versions).


    You said HEATING ELEMENTS, so it’s electric heat.


    I’m at home, so don’t have access to one presently.  Perusing the internet, it appears that the connector you referenced with an ARROW comes like that installed on a new control board.  Probably just a jumper plug with no wires to it.  If you don’t see some correlating wire harness laying in there without a plug on them, then don’t worry about it.


    The nature of your problem is way too broad to give you an answer to what your problem is.  Could be any number of things causing it.  You offered no results of any tests you might have performed to troubleshoot the problem.  Could be anything from an erroneous temp setting, a bad temp probe, a loose control connection at a contactor/solid-state relay, a critical electrical cable burned off behind the side panel…or a list of other things.  Ya never know until you see it.


    If troubleshooting electrical problems is not within your capabilities, then call a service company.  Those ovens are very complex in their operation.  Although the actual cause to the oven’s problem may be simple, knowledge of the oven’s overall system operation…along with skilled use of test equipment and experience in troubleshooting electricity – are key skills that are required for effectively resolving your problem.


    Doing a proper repair is kinda important too.

  • bush

    January 19, 2017 at 1:12 pm

    As I see it, your on/off pushbutton switches have been replaced with a rotary aftermarket control. Nevertheless, if it powers on your combi, that’s great.  For the elements to be energized, the controller needs to send a D.C. voltage to the solid state relays, to complete the circuit to the elements.  These relays are prone to failure, you will notice a change in design when you order the OEM replacement. (part# 40.00.453P).  Make sure the mounting surface is clean, and remember to tighten these relays securely to the heatsink. 

  • vtech

    January 19, 2017 at 3:18 pm

    Thanks for all the information! Much appreciated! . The serial number is: E21CA98071414.
     I have been an electrician for about 4 years now and I see this project is a bit outside my expertise, but i like it!. I have checked continuity on the heating elements and they seem fine. Checked all wires for damage, found some bad ones but that didn’t fix the problem. Checked all connectors and fuses. When going into diagnostic mode I am supposed to press key “5” and select the time 11:11 in time display at the same time, release key “5” and then pressing it again for function test.  It will not let me select time when pressing “5”. If I hold down the time button on the other hand, everything shuts off and the display changes between the real time and “001” if that means something. When the dry heating and time is set, the timer does not count down and I can’t hear any contactor switching on. No voltage through A1/B2 on relay which goes to the heating element as you foresaw. But there is no voltage differential on the controller that goes to relays when switching on/off heating, could the problem be here? Or would it be possible that all the relays have failed?  


  • ectofix

    January 19, 2017 at 3:20 pm

    AH…good eye, bush.  I didn’t see that rotary switch up there.


    I guess that was cheaper than replacing the whole board just to replace the OEM DPST push button switch that’s part of the board.

  • fixbear

    January 19, 2017 at 3:49 pm

    One should also have heat sink compound on hand for them.

  • bush

    January 19, 2017 at 4:12 pm

    I agree, I’ve used it also when the heatsink has some pitting or other irregularities.  These CPC combis will usually tear thru these relays because of failing elements in the steam generator.  I’ve considered placing metal oxide varistors across the terminals in an effort to protect them, but ended up having better results from adding a 3 pole varistor block that Rational offered as an upgrade.  When the last CPC unit in my territory finally is replaced I will celebrate!  The SCC versions are much more service friendly than the CPC or CM-P versions.

  • bush

    January 19, 2017 at 4:24 pm

    The diagnostic and function modes on these old units are frustrating to say the least.  But a word about these  solid state relays, think of them as a SPDT relay. You need power to enter at the common and from there it can be switched momentarily to the steam elements or momentarily to the hot air elements.  When proper temperatures have been reached there is no voltage output at all from the relay.  You may even experience low ampdraw from these relays when they are beginning to fail.  They are not cheap, and yes there have been times I had to replace all of them at once.    Good luck, you’ll fix it !

  • bush

    January 19, 2017 at 4:25 pm

    Sometimes a picture is worth a thousand words!

  • ectofix

    January 19, 2017 at 4:34 pm

    I see the other guys posted while I was typing.  I’ll put this here anyway:


    Great enthusiasm for stepping up to the challenge.  I like that.


    When you say key “5”, are you referring to how it’s numbered on a Service Reference chart?  That’s the button labelled PROG/START?


    Do you have an operators manual?


    Do you happen to have your hands on a training manual too?


    A schematic?


    Just wondering.


    DISCLAIMER:  Although I do have five CPCs, I’ve never encountered your particular problem.  Heck, I have a fleet of older C-line ovens and even more of the newer SCCs, too.  Their control boards are all different.  Doing a function test on the CPCs isn’t exactly straightforward, so I might’ve only tried it ONCE several years ago when I absolutely had to.  Otherwise, I can function test the newer ovens with my eyes closed (not really)


    As for an initial search for a problem, I would’ve initially done all of what you did (wires, fuses, connectors/connections).  I’ve found faulty board connections more than once that was the root to resolving a problem once I correct it. 


    FWIW, The board on the control panel is primary just the user interface.

    Of those stacked boards BEHIND the control panel

    • The top one is the CPU.  It does all the sensing.
    • The bigger one behind it is the I/O board.  It receives the various input voltages and direct that to wherever it’s designated to go throughout all three boards.  Of course, it energizes everything, depending on operational mode (steam, combi or air).


    So…what heat is NOT working? Air?  Steam?  BOTH?


    What ACTUAL cabinet temperature is the oven seeing (sensing)?  By default, the oven displays set temperature.  Push and hold in the temperature button (I think) and it will display will show you ACTUAL temperature.  If there’s a probe issue, it may not be calling for heat if the probe circuit is satisfied by a faulty probe.


    FYI.  If you find that the probe may be questionable, those probes are type K thermocouple and are easy to test.  Do so by immersing the probe tip in an ice bath.  Set you digital meter to temperature.  While observing proper polarity and with the probe leads isolated from the board, connect your test leads to the probe leads.

  • john

    January 19, 2017 at 5:29 pm

    Was the CPC one of the Rationals you completely disassembled and remanufactured in that YouTube video? I was looking for it but couldn’t find the link. Quite a job there, ectofix

  • vtech

    January 19, 2017 at 5:49 pm

    Yes, key “5” is the button labelled PROG/START. Everything i know so far is from reading the “Training Manual – Diagnostic and troubleshooting – SCC Line/SelfCooking Center – Combi Master” which I found searching the internet. I have checked every connection on every board behind the control panel. Hot air, steam, nothing works. Only the fans.The actual temperature  when starting up is about 20℃/ 68℉ (same as room temperature) After 40-60 minutes of running the temperature is 40℃/104℉. I suppose that is the heat coming from the motor/fans? I can push a 1/2 button for the fans to run slower, thats about it. I will first check the relays, the probe, some more around the boards, wires, steam elements and hopefully get it up and running soon. Thank you all for very detailed answers.


  • fixbear

    January 19, 2017 at 7:34 pm

    How about using MOV’s and a cap

  • ectofix

    January 19, 2017 at 7:46 pm

    Thanks John.  No, that oven I rebuilt was a 2010 model SCC.  Vtech’s oven is an earlier CPC oven line.  They were made from 1997-2004.


    Although plagued by its aged and less refined technology that seem sub-standard when compared to our newer stuff, the CPC was a benchmark product of its period.  They were certainly built better than the newer ovens.  Otherwise I wouldn’t have been having to bolster a bent and failed frame pan with plate steel.


    Here’s what John was referencing. A SCC101G.  About a six week project (awaiting parts and all).  I’m in-house, so it was in our shop.  Bush and any other field techs would NEVER do or persue this – since a customer’s cost would be prohibitive:




    I spent so much time/thought on this oven, I had to commemorative my efforts somehow.  So…I did a vid.

  • vtech

    January 21, 2017 at 2:08 pm

    An update so far.

    Began removing the relays for proper cleaning and testing. Heat sink compound has been ordered and will be applied as soon as I get it. Both section A and section B on all relays seems to be operating normally. I found datasheet for a similar Crydon relay, stating the control voltage range needed to be 3,5-32VDC and minimum input current (for on state) were 10mA. So I used a 9V battery and a fan for the testing.

    After removing the CPU and the I/O board for inspection, I came across a damaged/burned relay on the board behind the CPU. Could this be causing the problem? And if so, would it be possible to get this relay replaced, or do I have to replace the entire board? I have a suspicion this I/O board is not as cheap as I want it to be


  • ectofix

    January 21, 2017 at 6:18 pm

    That is a problem, but probably not the one that’s keeping it from heating.


    Looking at your bottom-left picture, is that connector X4 of board A2?  If so, then per this diagram (that I really shouldn’t be sharing):

    …that burnt terminal set you see there leads to pin 5 of X4.  Per a schematic, pin 5 goes to the SC pump (“self-cleaning” or emptying pump).  SO…the SC pump obviously won’t work.  As a result, that means the steam generator is probably full of rock.  That means you’ll need to put your electrical prowess aside, pull the steam generator, remove the elements, then break out the hammer and chisel to extract the limescale formation in it.  Maybe replace the pump and a few elements to boot.


    Oh YES, combi-ovens do present new and unique challenges an electrician typically may not consider or be prepared to address.


    From a schematic I looked at, the X3 connector outputs to the SSRs.


    I’m still thinking that since there’s no call for heat, there’s a central issue that’s preventing the SSRs from being energized.  Maybe a failed wire connection.  Possibly a faulty relay that’s integral to that expensive board.  Or…possibly an issue with a sensing circuit that’s saying “we don’t need heat yet“.  Maybe a component failure on the board that’s not visible.  The “black box” theory then needs employed to troubleshoot it.

    • Is the box (board) getting proper inputs?
    • If so, then is it providing expected outputs?
      • If YES, then the problem lies elsewhere.
      • If NO, then the box is at fault.


    You gotta know what’s expected to go that route.


    Concerning that burnt section on the board…unless you’re into researching, ordering and soldering in small relays and repairing fried IC board circuit tracks (I’ve used phone cable wire once or twice), you’ll need to order a new board set (A2 and A3 together).  From a commercial food equipment technician’s standpoint, soldering in little relays to fix a board is not even an option.

    I HAVE replaced just a relay on a board before (for whatever equipment it was), but v-e-r-y rarely.  Even an IC chip.  Doing so resulted in extensive down-time, since I wasn’t exactly hitting upon a well-developed parts stream to achieve a repair.


    Replacing the OEM board might be expensive, but it’s simpler and FAR faster.  OH…and YES, that board is not cheap.  I don’t know if this is the exact part number for your particular oven, but here is a representation of one:




    The schematic that’s hopefully still with the oven will have the part number for the correct board listed there within the last few pages.


    Sure wished I could be there with you to look at that.  Looks like an interesting problem.

  • fixbear

    January 21, 2017 at 9:13 pm

    Did anyone notice that it arced across the normally open to the normally closed terminal of the relay? Something had to start that track like a conductive film or very high voltage.going from on to off. It never arced to the common terminal. What amperage is it fused at?


       Alternatly the relay contact may have been at end of life and had a arc pit that created resistance and heat to the NC terninal causing the solder to soften and melt.

  • vtech

    January 24, 2017 at 3:48 pm

    Oh, thanks! Yes, that is connector X4 on board A2 and is fused at 2A.

    I removed the steam generator, did not look as bad as expected. Cleaned the elements and tested the pump, seems to be working fine. It may need some new high temperature insulation foam on the generator which I am going to order after knowing it will run properly.  I am going to clean the box under the generator as well. After opening a hatch on the side I got a hold of a loose tube along with what may look like a rubber seal, cannot say I know what it does, but will for sure get it back in there.


    Transformer is working fine, so the the pcb is getting correct input voltage. I will continue to look for bad wire connections, sensors and then measure all outputs on the board and hopefully find a fault that is visible and not located on the board. Will let you know if I find anything interesting.

    I ordered the relay and will try to solder it on with a phone cable as you mentioned. Thanks for all the useful information so far.


  • fixbear

    January 25, 2017 at 1:48 pm

    What is the voltage across that relay?  And isn’t there contractors for the heaters?. Or are they using the solid state ones on the heat sink for switching?


    Noticed that to top right on the heat sink got hot enough to bake the coumpound. Four others also show high heat.  Is the cooling fan working correctly..

  • ectofix

    January 25, 2017 at 5:13 pm

    There’s just a single general purpose type contactor for main power in.  That oven’s made in Germany, so it’s either a AEG (GE) or a Benedikt & Jäger contactor.  The B&Js are the newest ones available.


    The control of heat to the oven cavity (air) elements or the steam generator elements is through the Crydon solid state relays.  Each of those work likes a SPDT switch to power the elements – depending on which SSR terminals get a DC input from the relevant temp control circuit.  The oven is designed to energize EITHER the steam elements OR the air elements, but not both simultaneously…as bush said.

  • fixbear

    January 26, 2017 at 11:43 am

    That explains a lot. Any reduction of air flow over those heat sinks and good bye SCR’s.


    Surprised that the aren’t Klockner Moelner part’s in a German machine.

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