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Micro-wave Daewoo KOC-972T TRANSFORMER problems

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JohnMcC

Member
Hi,

HELP PLEASE !

Daewoo no longer supply this transformer.............am trying to find a solution.
It is the L.V. transformer.

Info and photos, and service manual :
https://1drv.ms/f/s!ArIK6n3A4oCfgZ9MemDRHq8KfXaWLw


I have established :

DMR-101FS, 5EPV041351, SEGI 98.J26 A

Terminal 1-2 230 VAC /50Hz
Terminal 4-5 13.0 VA C
Terminal 6-7 35.0 VA C
Terminal 8-10 3.0 VA C

but this is not clear to me................on terminal 4-5 ...........is 13.0 VAC the watts (volts x amps) or the voltage AC ?

I came across this webpage looking for a replacement transformer:
http://articulo.mercadolibre.com.ar...rmador-para-placa-de-microonda-dmr-101-fs-_JM

but I am not prepared to pay 150 dollars for a second hand transformer, and it does not seem to correspond exactly anyway ??
Please refer to attached photos.

Many thanks for any help or ideas you may have to offer.

Kind Regards,
John
 

Attachments

Les Jones

Well-Known Member
Most Helpful Member
Hi John,
If there is room in the microwave cooker for an extra 13 volt transformer then provided there are no shorted turns on the primary you could connect the 13 volts ac from the extra transformer to the 13 volt winding on the original transformer. That would feed the 12 volt rail and the 13 volt winding on the original would behave as a primary to provide the two other outputs. If you have already damaged the original primary then you would have to carefully remove it.

Les.
 

JohnMcC

Member
Hi Les,
Unfortunately I have mucked up the original transformer completely.
From memory the secondary coils all had continuity but the primary coil was open circuit, so already damaged.
Note that I have already removed the transformer from the circuit board, that is quite easy to do.

Since trying to establish whether there was a thermal fuse, I have mucked up the secondary windings as well

In the microwave enclosure there is room to fit other transformers, even if I cannot make them surface mounted on the circuit board like the original.
I am happy to place other transformers in the box/enclosure somewhere and solder wires.

Thank you,
John
 

spec

Well-Known Member
Most Helpful Member
Hi,

HELP PLEASE !

Daewoo no longer supply this transformer.............am trying to find a solution.
It is the L.V. transformer.

Info and photos, and service manual :
https://1drv.ms/f/s!ArIK6n3A4oCfgZ9MemDRHq8KfXaWLw


I have established :

DMR-101FS, 5EPV041351, SEGI 98.J26 A

Terminal 1-2 230 VAC /50Hz
Terminal 4-5 13.0 VA C
Terminal 6-7 35.0 VA C
Terminal 8-10 3.0 VA C

but this is not clear to me................on terminal 4-5 ...........is 13.0 VAC the watts (volts x amps) or the voltage AC ?

I came across this webpage looking for a replacement transformer:
http://articulo.mercadolibre.com.ar...rmador-para-placa-de-microonda-dmr-101-fs-_JM

but I am not prepared to pay 150 dollars for a second hand transformer, and it does not seem to correspond exactly anyway ??
Please refer to attached photos.

Many thanks for any help or ideas you may have to offer.

Kind Regards,
John
Hi John,

Can you give the dimensions of the transformer?

spec
 

JohnMcC

Member
Hello Spec,

Yes of course

41mm..............length along the terminals
47mm..............height at the transformer is sitting on the board
33mm..............width

John
 

spec

Well-Known Member
Most Helpful Member
Hi John,

I think you can provide all of your voltage supply lines on all equipments by simply fitting one new transformer for every secondary voltage of the original transformer. From the size you give for the transformer it is not very high power. From what I see suitable transformers are available on the net, mainly from ebay.

Would this approach suit you?

spec
 

spec

Well-Known Member
Most Helpful Member
POST ISSUE 05 of 2016_11_09

Hi John,

Some of these replacement transformers do not produce the exact same voltage as the original transformer but don't worry about that for the time being. Just consider the physical aspects- that is will the transformers fit your equipment?

MICROWAVE VOLTAGES

Terminal 1-2: 230 VAC /50Hz primary

Terminal 4-5: 13V
([email protected]) http://www.ebay.co.uk/itm/CTFP6-12-Camdenboss-Transformer-6Va-2X-12V/361649610228?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=39829&meid=eae03b02e1c3433c9904ea6f61ac8887&pid=100005&rk=4&rkt=4&sd=131911297123

Terminal 6-7: 35V
(2*[email protected]) http://www.ebay.ie/itm/Encapsulated...hash=item2a1b163b77:m:mZyvhEy-bcWlksgtjwXKggQ

Terminal 8-10: 3V
(2*[email protected]) http://www.ebay.co.uk/itm/CTFC6-4-5-Camdenboss-Transformer-6Va-2X-4-5V/131911297123?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=39829&meid=f5dbae62f15b49579d3c83250a8e9cc8&pid=100005&rk=3&rkt=6&sd=142129561727

(2*[email protected]) http://www.ebay.co.uk/itm/TRANSFORMER-6VA-2X-4-5V-Part-Number-CTFC6-4-5/391358005334?_trksid=p2047675.c100005.m1851&_trkparms=aid=222007&algo=SIC.MBE&ao=2&asc=39829&meid=eae03b02e1c3433c9904ea6f61ac8887&pid=100005&rk=2&rkt=4&sd=131911297123


OTHER TRANSFORMERS
(2 x [email protected]) http://www.ebay.co.uk/itm/2x24V-12VA-Chassis-Clamp-Mounting-Mains-Transformer-Double-Secondary-Winding-New/401169631870?_trksid=p2047675.c100009.m1982&_trkparms=aid=888007&algo=DISC.MBE&ao=1&asc=39829&meid=146241f7eb0b4128b2a8869c93262069&pid=100009&rk=1&rkt=1&sd=162110650655

(2 x [email protected]) http://www.ebay.co.uk/itm/Transformer-power-mains-230V-12VA-0-20V-300mA-0-20V-300mA/291931037214?_trksid=p2047675.c100009.m1982&_trkparms=aid=888007&algo=DISC.MBE&ao=1&asc=39829&meid=fffbbf302bed4734b80f91a487478f37&pid=100009&rk=1&rkt=1&sd=401169631870

([email protected]) http://www.ebay.ie/itm/BVEI3052895-...779483?hash=item2cb310bc5b:g:ErEAAOSw4shX7Qvl

SUPPLIER WITH GOOD RANGE OF TRANFORMERS
http://www.ebay.ie/itm/Encapsulated...hash=item2a1b163b77:m:mZyvhEy-bcWlksgtjwXKggQ
 
Last edited:

Les Jones

Well-Known Member
Most Helpful Member
Hi spec,
I think the 3 volt winding needs to be fairly close to 3 volts as it feeds the fluorecsent display filament. It also needs to be centre tapped. This is the schematic of the control board. (From the service manual.)
Screen Shot 11-08-16 at 07.43 PM.PNG
This is some information on the transformer.
Screen Shot 11-08-16 at 07.46 PM.PNG
This information does not show the centre tap but it is shown on the schematic.

Les.
 

spec

Well-Known Member
Most Helpful Member
Thanks Les,

I was thinking of reducing the 4.5V by putting some diodes in series with the windings to make the RMS value the same On a different tack, presumably the power for the florescent heaters can be DC.

spec
 

Les Jones

Well-Known Member
Most Helpful Member
Hi spec,
I have never used fluorecsent display so I know almost nothing about them. I did a bit of Googling about them last night with respect to the freezer. I was trying to find if the filiments ran from some standard voltage (Like a lot of valves had 6.3 volt heaters.) I noticed a mention of a problem with different parts of the filament being at different potentials causing variation of the brightness of segments. I did not read it in detail as it was not the information I was looking for. I think this is the reason the DC "cathode" connection is made to the centre tap of the transformer. We could use resistors to drop the voltage if we measured the current that the filaments take. We could alo create an artificial centre tap with two resistors. I imagine (But dont know.) that the "cathode current would be quite low so the resistors used would not need to be too low a value. (Wasting power and producing heat.)

Les.
 

spec

Well-Known Member
Most Helpful Member
Hi spec,
I have never used fluorecsent display so I know almost nothing about them. I did a bit of Googling about them last night with respect to the freezer. I was trying to find if the filiments ran from some standard voltage (Like a lot of valves had 6.3 volt heaters.) I noticed a mention of a problem with different parts of the filament being at different potentials causing variation of the brightness of segments. I did not read it in detail as it was not the information I was looking for. I think this is the reason the DC "cathode" connection is made to the centre tap of the transformer. We could use resistors to drop the voltage if we measured the current that the filaments take. We could alo create an artificial centre tap with two resistors. I imagine (But dont know.) that the "cathode current would be quite low so the resistors used would not need to be too low a value. (Wasting power and producing heat.)
Ah yes, a heater just like vacuum tubes, sorry valves, I was forgetting you are a Brit:). I might have know you would come up with a good solution to the higher voltage; resistors, I like it and F#@k global warming.:D

The substitute transformer is 4.5V-o-4.5V, so a couple of resistors will do nicely. I wondered what all these 3V AC lines were for on older equipment!

spec
 

JohnMcC

Member
Hi Spec,
From your post no.8 I understand that I need 3 transformers ideally with the following characteristics:

1) Primary 230 VAC /50Hz ................Secondary 13 VAC rating 6 watts
2) Primary 230 VAC /50Hz ................Secondary 35 VAC rating 10 watts
3) Primary 230 VAC /50Hz ................Secondary 3 VAC rating 6 watts

As these secondary voltages are not available on standard transformers, the idea will be to obtain a similar secondary voltage, and add a resistance when the replacement transformer voltage is too high (on the secondary side).
Is this correct please ?

In the example of requiring "Secondary 13 VAC rating 6 watts", how is this obtained from a 2x 12VAC output, or are we assuming that 12vAC will be close enough ?

In the example of requiring "Secondary 35 VAC rating 10 watts", is this obtained from a 2x 18vAC output put in series to obtain 36vAC ?
(I do not remember enough about transformers, but I seem to recall that two outputs should not be joined in series because it would burn out the coil ????? Phase and all sorts of other problems ??)


I am trying to educated myself as we go along !!!

PS: I will be away from this Friday morning (11th Nov) until the end of the weekend...........so that is why I will be going "quiet" on the Forum and replies !!

Kind Regards,

John
 

spec

Well-Known Member
Most Helpful Member
Hello John,

Hi Spec,
From your post no.8 I understand that I need 3 transformers ideally with the following characteristics:

1) Primary 230 VAC /50Hz ................Secondary 13 VAC rating 6 watts
2) Primary 230 VAC /50Hz ................Secondary 35 VAC rating 10 watts
3) Primary 230 VAC /50Hz ................Secondary 3 VAC rating 6 watts
I think the volts are right. But it may be safer to increase the '13V' transformer to 10W.

As these secondary voltages are not available on standard transformers, the idea will be to obtain a similar secondary voltage, and add a resistance when the replacement transformer voltage is too high (on the secondary side).
Only the 4.5V heater transformers will require resistors to make the heating effect the same as it was with the original 3V

In the example of requiring "Secondary 13 VAC rating 6 watts", how is this obtained from a 2x 12VAC output, or are we assuming that 12vAC will be close enough ?
Yes 12V will be OK. But I will see if I can find another transformer with a single 12V winding.

In the example of requiring "Secondary 35 VAC rating 10 watts", is this obtained from a 2x 18vAC output put in series to obtain 36vAC ? (I do not remember enough about transformers, but I seem to recall that two outputs should not be joined in series because it would burn out the coil ????? Phase and all sorts of other problems ??)
Yes, the two 18V winding will be connected in series to produce 36V, which will be fine.

There is never any problem connecting transformer windings in series, and in most cases, if the secondary winding are the same voltage, mostly you can connect the winding in parallel. But you must connect the right ends of the winding. If you connect the wrong ends you will get a short circuit. If you connect the wrong two ends of the winding together in series, you will not do any damage, but instead of getting double the voltage, you will get 0V.:D

I will be away from this Friday morning (11th Nov) until the end of the weekend
Have a good weekend and don't worry about freezers, cassette HiFi, or microwaves... or the dire consequences of connecting transformer secondaries in series. :D

spec
 
Last edited:

JohnMcC

Member
OK, thanks !

Horrible weather here...........I understand it is very cold in the UK as well, and that you can expect a Siberian winter
 

spec

Well-Known Member
Most Helpful Member
OK, thanks !

Horrible weather here...........I understand it is very cold in the UK as well, and that you can expect a Siberian winter
Bright, sunny cool and windy- quite pleasant.:)

Cheers

spec

But there has been an earthquake- Donald Trump just got voted presedent elect of the USA.:D
 

Les Jones

Well-Known Member
Most Helpful Member
Hi John,
You can only use a resistor to drop the voltage if you know the current drawn is going to be stable. (As is the case with the 3 volts that supplies the filament on the display. I think this draws about 60 mA) I think (But cannot be sure.) that 12 volts will be close enough to the 13 volts of the original transformer. If you get a transformer with slightly higher current (Or VA) rating than reqired it wil probably give a slightly higher voltage than its rating. Using a 2 x 12v transfomer you could just use one winding provided the rating is twice as much as required. You can parallel the windings if you are sure they have EXACTLY the same number of turns on the secondary. I would normaly only do this with a toroidal transformers as bothe secondaries are wound at the same time. I also think the 2 x 18V transformer will be ok to replace the 35 volt one. One thing we could do to reduce the voltage from the 4.5 - 0 - 4.5 transformer would be to feed the primary from the 110 volt tap on one of the other transformers if it has this tap.

Les.
 

spec

Well-Known Member
Most Helpful Member
Hi Les,

What do you think about the VA ratings of the replacement transformers. For example if the heater current is only 60mA that equates to 4.5V* 2 * 0.06A= 0.540VA, so a smaller transformer should do for the 4.5V transformer.

Incidentally, another way to reduce voltage is to connect a couple of back to back diodes in series with the winding. Each pair of diodes would reduce the voltage by 0.6V to 1V depending on the current.

spec
 
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