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Old 30th Mar 2020, 3:40 pm   #1
1955APREN
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Default Samsung CW21Z403 crt TV

This set is 20yrs old and has been used as our main set till 18 months ago, when it was taken up to my shed. A few weeks ago it started doing erratic things like going to AV mode & taking a long time to start up, both faults being intermittent . A Few day's ago it stopped working altogether. My thoughts made my think that is was a cap in the power supply, but yesterday I removed all on the secondary side but all checked our on my tester as OK. I then replaced both small caps on the primary side. Set still dead. There are two large diodes on the sec side of the transformer, one has 4.7v on its cathode, the other 92volts on it's cathode.
By the one that has 4.7v on it there is a mark on the pc that shows 6.7 volts at this point.

I would like to hear if anyone has had this fault, or has any one got a circuit diagram of the power supply of this set.
Thanks
Derrick
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Old 5th Apr 2020, 7:55 pm   #2
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Default Re: Samsung CW21Z403 crt TV

Up date
I spent all afternoon on this set . Found out that it was made by Thomson in Hungry . So its not a Samsung only badge up set. It uses a Strw750f as the power regulator . I cannot find any information on this device . Does any one know if other tv's uses this device. So at least I would know what the pin layout is.
Thanks for any information
Derrick
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Old 5th Apr 2020, 8:37 pm   #3
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Default Re: Samsung CW21Z403 crt TV

I cannot even find a reference to that model number, do you know what chassis it uses? this is often marked on the silk screen of the main pcb or on the rating/model plate on the back of the set.
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Old 5th Apr 2020, 11:14 pm   #4
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Default Re: Samsung CW21Z403 crt TV

First things first, isolate the line stage and power the set up and see if the PSU and standby LED come on.
Incidentally, Google shows a few results for this set if you look for CW21 Z403 samsung. User manual
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Old 6th Apr 2020, 12:09 pm   #5
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Default Re: Samsung CW21Z403 crt TV

It would be unusual for Samsung to use a Thomson chassis - in my experience they always use their own.
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Old 6th Apr 2020, 12:33 pm   #6
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Default Re: Samsung CW21Z403 crt TV

A picture of the type label and one of the chassis in general might lead to recognition.

Also, while I know for sure that Samsung had a Hungarian factory, I don't think Thomson had one. Maybe it's only the picture tube that was made by Thomson (likely their Polish factory)?

A quick look learns that the chassis designation is likely S16D.
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Old 6th Apr 2020, 9:31 pm   #7
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Default Re: Samsung CW21Z403 crt TV

Thanks
Ben
Glyn
Maarten
thank you all for your input regarding this set . I am enclosing photo's of the set
there's label near the line out transformer that as some further letter's on it after the model no cw21z403n --cxxeu and the word Thomson . Inside the back there is label Hips v2 2006.07.1( this might just apply to the back).
The crt is made by Thomson in Poland .
Today I just plugged in to the mains and the set came straight on much to my surprise at least I Had raster covered in snow after a few mins I switch off to connect a scart lead but on switching back on set dead again low voltage on the
diodes as per post 1. When the set was on menu button did not work .
Derrick
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Old 6th Apr 2020, 10:11 pm   #8
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Default Re: Samsung CW21Z403 crt TV

The HIPS thing is High Impact Plastic or something. Used for the cabinet.

A little bell is ringing in the back of my mind about low voltage zener diodes in the PSU giving trouble with these later Samsung sets. Will try and find some repair notes but it has been about ten years since I last fixed one. That chassis looks quite Samsung-y to me!
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Old 7th Apr 2020, 2:35 pm   #9
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Default Re: Samsung CW21Z403 crt TV

The chassis is definitely Samsung. The name Thomson refers to for which picture tube it's configured. Could probably also say things like SDIG (Samsung), Ekranas or LPD (Philips) on other models.
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Old 7th Apr 2020, 11:06 pm   #10
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Default Re: Samsung CW21Z403 crt TV

Look on the board underside near the line o/p transformer, Samsung sometimes printed the chassis reference there, e.g S51, S53A
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Old 8th Apr 2020, 12:17 am   #11
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Default Re: Samsung CW21Z403 crt TV

Quote:
Originally Posted by ben View Post
....A little bell is ringing in the back of my mind about low voltage zener diodes in the PSU giving trouble with these later Samsung sets. Will try and find some repair notes but it has been about ten years since I last fixed one. That chassis looks quite Samsung-y to me!

I have heard of intermittent zener diodes causing trouble also, although no idea what brand set they were in, but that would seem to fit the symptom of randomly low voltage. (assuming the voltage was measured correct when the set decided to work?)
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Old 8th Apr 2020, 6:53 am   #12
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Default Re: Samsung CW21Z403 crt TV

the only note I have for zeners is for the CW21A113V not sure if same chassie
ZD810 27v 1W zener, if R807 & R808 are both wire links replace 1 with 6R8 .5W or zener will fail again
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Old 8th Apr 2020, 8:41 pm   #13
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Default Re: Samsung CW21Z403 crt TV

Thanks everyone for your help
chassis type is S16D
Its as some zenner"s diodes near to the str heat sink.
Not had a lot of time today will hope to remove these tomorrow and order new ones ( if I can read what voltage they are). It also as wire links but resistor is 6r8 more like 22r
I will let you know when I have fitted new Zener,s
Kind regards
Derrick
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Old 8th Apr 2020, 9:39 pm   #14
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Default Re: Samsung CW21Z403 crt TV

Here is a diagram for that chassis, although not that model, so use caution as actual components/values fitted to your set may differ. Better than nothing I suppose.
It is a bit confusing as the chopper chip is marked as two different types, one of which is yours.
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File Type: pdf samsung_cs21z40zqcxbwt_chassis_s16d_sm.pdf (1.52 MB, 85 views)
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Old 10th Apr 2020, 8:12 am   #15
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Cool Re: Samsung CW21Z403 crt TV

Thanks Red to Black
Just what I needed . regarding the two str.s used it just say.s change, but does not give any circuit changes . Even more confusing the the diodes marking on the pc have the ref ZD when in fact some are just diodes ex ZD816 is a 1N4148
I am going to order zener diodes today and will report back when fitted
regards
Derrick
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