Rational cpc 201 heating element problem

[vtech]

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]

How about using MOV’s and a cap

[ectofix]

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:

 

COMPLETE COMBI-OVEN REBUILD: Before & After

 

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

[vtech]

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]

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:

 

RATIONAL PCB POWER SUPPLY/CPU W/O EPROM

 

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]

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]

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]

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]

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]

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.