Advice sought to repair cooker module Electrolux EPSOPMSS

[leavemetogetonwithit]

Wanna have a go at this meself as a learning experience.
Have already repaired burnt tracks and replaced triac, still no go.
Noted: pcb mounted trasformer :230v pri. 10v (yes, ten) secondary according to what’s printed on it. But it only gives out 2.5v according to my meter.(And gets v. hot). This is then followed by 4 diode rectification to a L7905CV voltage regulator (That means 5v doesn’t it?). Can’t find a 10v TXF anywhere (tried RS & Maplin). Would 9v be OK? Printing on original reads 230v/50Hz/24ma(1-5) & sec. 10v /0.32A(7-9) (Just realised bracketed no’s could refer to terminals?)

Appliance 18 m. o. approx. New module £90 + retail
QER would ‘ave a go at £40 + but, as I say, I wanna do it meself if poss.
(Another reason is I’m not sure WHY it blew up ).

Off to work now. Be back tonight. Please have answers by then. 😆

[Tubs]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Hi there,

Its the VA rating of the secondary winding that matters. dont see it to be too much of a problem as you are supplying a 5v regulator (which if memory serves me correct needs a minimum of 7v supply).

At 9 volts you would need a current rating of .35 amps, in order to give you the same VA rating.

Hope this helps

Steve

[andy2]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

lmtgowi – Hows about posting with your name?

Your best bet with this is to start from the output of the power supply and work backwards / forwards. If your transformer output is low and getting hot then it is probably another componant that is dragging the voltage down, Usually a s/c componant that sits across the supply rail.

If you can, isolate the power supply itself first and see if you are getting 5v out. If you are then the problem is elsewhere on the board.

If the problem is on the supply check electrolytic smoothing capacitors and the regulator itself

have lots of fun

Andy 🙂

[andy2]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

PS – forget the “the problem is elsewhere on the board” bit as I think these regulators are s/c protected so any s/c across its output should not draw excessive current from the other power supply componants ??

ie. the problem is in the supply itself.

[leavemetogetonwithit]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Thankyou gentlemen,
I’ll go away and do some more measuring.
Mike.

[Brains]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

If you are not getting 5V out, check the regulator by replacement. Also check that the rectifier bridge does not have a shorted diode.

Regards

[leavemetogetonwithit]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

OK.
Had a break to watch some TV. Wish I hadn’t bothered.
Desoldered diodes/txf ends. Now txf o/p measured 13v.
Resoldered in, re-measured 2.5v or so.
Pulled out voltage regulator. Now have abt. 17v dc
So it’s the regulator, ain’t it?
I(input?) on reg is short to tab,so is G(gate?). O(output?) is o/c to tab and to other two legs.
Transformer still gets hot but maybe it’s just meant to?(says on it “hipot 4kv ta 70* C/F”)
Will order a couple of regulators, some triacs,diodes and maybe a relay or two in anticipation of future fun, as that’s the way the world seems to be going.
Thanks to you all.
Will update on progress.
Mike.

[Brains]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Yep. You you’ve got it. Its the regulator. RS Comps will have these. 😉 Have fun.

[leavemetogetonwithit]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Have put in new regulator. Put mains on again. (This is off appliance w. no other components connected.) Now have abt. 2.5v between “gnd” and “I” and same between gnd and “O”. But only 0.17v between I & O
Also regulator quickly heats up. All diodes check OK. (except a little pink one way down the line which probably would check OK if I desoldered it).
Well maybe it has to be connected up with timer board and elements before it’ll act like I expect it to?
Anyway, most of the rest is smd’s and a couple of chips so if it don’t work now it’s going to QER methinks.
Thanks for the help guys. 🙂
Will update in a few days.
Mike.

[Brains]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Do you have access to an oscilloscope? If yes, take a look at the ripple. From what you describe, i think that that a lot of current is being pulled from the regulator. With the testing you have just done, is this with the load connected or disconnected?

Is the diode connected across the regulator output i.e cathode to + & anode to ground? In my view you may have a shorted capacitor that damaged the original regulator.

I would take the regulator out so that the unregulated side is running unloaded, check the ripple with the scope. If okay, use your meter from the 5V rail to ground and see if there is a short. If yes, then check the caps & then the ICs.

Be interested to know how you get on.

[leavemetogetonwithit]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

“Do you have access to an oscilloscope?”
Used to have one but sold it ‘cos it never got used!
“If yes, take a look at the ripple.”
Not sure I’d know what was normal anyway.
“From what you describe, i think that that a lot of current is being pulled from the regulator. With the testing you have just done, is this with the load connected or disconnected?”
Load(as in cooker elements and timer module) is all still at the customer’s house. Otherwise, last test described made with all elements on board still soldered in.

“Is the diode connected across the regulator output i.e cathode to + & anode to ground?”
There is a smallish red diode just downstream from the regulator. Its plain (no line) end is connected to O on the reg. The other end goes off to various smd’s.
“In my view you may have a shorted capacitor that damaged the original regulator.”
There are only 4 electrolytics on the “component”side of the board. The largest, nearest to the reg., 220u 35v, checks ok (in circuit) with an old analogue meter on the 1k scale.The others are less sure. Perhaps I should just try replacing them all?

“I would take the regulator out so that the unregulated side is running unloaded,”
Isn’t that what I did before?Oh no, you’re right, I disconnected at the unrectified side of the diodes before.But the rectifier diodes have all checked OK so I think you’re right that the problem will be downstream.

” check the ripple with the scope. If okay, use your meter from the 5V rail to ground and see if there is a short. If yes, then check the caps & then the ICs.”
With ICs, Iwouldn’t know where to start.

Be interested to know how you get on.
Have just checked between regulator I & O (in circuit) and it looks like it may have been damaged again as resistance is low.
I very much appreciate your help Brains 🙂 , however I’m beginning to think QER now as customer is probably getting anxious.(And the fun’s wearing off). 🙁

[leavemetogetonwithit]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Replaced all four electrolytics this morning. Still have same voltages. 😕
Could it be that it is nevertheless OK/fixed ❓
Didn’t want to take it round and go through all that again with so much doubt, so rang customer and explained situation. She says time now more important than money, go for brand new part @ £90 odd.
OK so I get on to my Distriparts man and his exploded diagrams don’t quite tally with mine 🙄 . Therefore am posting now in trade spares to get correct part no. 😉
When,probably in a week or so, I have that then I’ll take the old one with me too and give it one last try.
Meantime, any further ideas 💡 welcomed. 🙂
Mike.

[Brains]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Mike

I doubt the problem is fixed by replacing the caps – especially if you are getting the same volts. The LM78/9xx series regulators will run without a load. This ‘smells’ like SMDs now. If your customer is giving you hassle, you may be better off to get a new module & try to fix this one when you have a quite few hours 😆 . Since the other parts are surface-mount, then you are dead-in-the-water without a rework station 😥 If you don’t have shaky hands, you may get lucky if the smds are three leg transistors & you have a small soldering iron 🙂

Be aware that there is a risk that the timer module (left in the cooker) may also be damaged 😥

Hope it all works out. Again, be interested to know the final outcome.

[Brains]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Mike

Just read the first post again. I note that the triac had popped. Heres a thought. See what you think. The triac will probably be driven by an opto-coupler. Assuming that the triac failed shorted with either a short from MT1 or MT2 to gate, I am almost willing to bet that the opto-coupler has died. This could be pulling your 5V rail down. Also see if you can sus out how the opt-coupler is driven. Whatever drives the opto also has probably died.

[leavemetogetonwithit]

Re: Advice sought to repair cooker module Electrolux EPSOPMS

Hi Brains,
Thanks first for reminding me about the timer module. I’ll give it a closer visual check again when I go back,and cross my fingers. 🙂

Looking at the only diagram of an opto coupler I have to hand, a Maplin catalogue, it has 4 feet. I can’t see anything on this board with more than 3 and less than 14. ❗ The triac’s gate is fed via a resistor from one of the penultimate legs on the main IC. This last has a label:”SPOBT230HEX
28077729-0 Ind A 05F0″ Maybe it has an opto-coupler in it? I’ll have a look at RS site later and see if I can find it.

💡 Would I risk damaging the new board if I linked it up to the mains to test voltages the way I’ve been doing with this one ❓

This has been fruitful so far in that I have re-learned a few things I had forgotten and improved my soldering technique somewhat. (Although you might be a bit 😯 if you could see this board now!)
Cheers,
Mike.

[Author]

Posts