CTV Telefunken MNR28

Posted by: @ralph

I am looking for televison magazine june 1989 for wiring diagram. I suspect the eat transformer but it is not found. Can you help me?

They are all here for download

https://worldradiohistory.com/Practical_Television_Magazine.htm

Thanks for your help. time ago i used a tester with ne555 to see the primary of the eat transformer if it was shorted. it would be interesting to build it but i don't remember where it is.

If you have an oscilloscope, a very good method is to ring the winding. If you're not familiar with the procedure, see here https://www.radios-tv.co.uk/vintage-electronics-blog-forum/333-2/

good morning for the telefunken mnr28 which turns on the yellow led then turns off I have to check the pin 15 of tea2029? what voltage should I have?thanks.

Posted by: @ralph

pin 15 of tea2029? what voltage should I have?

Taken from the Datasheet

V.7.4 - Power supply soft-start TEA2028/29

When the TV set is initially turned on, control pulses are not yet available and consequently the controller block on primary side will impose a low-power transfer to the secondary winding. This power is produced by an intermittent switching mode called ” Burst Mode”. As soon as the VCC supply to TEA2028/29 exceeds 6V level, line and SMPS outputs are enabled. Since the filtering capacitors on the secondary side cannot charge up instantaneously, the voltage to be regulated would not yet be at its nominal value. Without conduction period limitation upon start-up, the de-vice will set a maximum cycle of 28μs which will result in a high current flow through the primary winding and thus through the switching transistor, which will in turn activate the protection function implemented on the primary side. Consequently, the primary controller block will be inhibited, and the set will not turn-on. A start-up system has been implemented within TEA2028/29 to overcome this problem. This soft start system, will, upon initial start-up, use the image of the falling voltage on Pin 15 to in-crease progressively the conduction cycle. The phase modulator ”M2” compares this voltage with line saw-tooth voltage and delivers the correspond-ing limitation cycle. During supply voltage rising cycle [VCC(Pin 8)< 6V], the capacitor Pin 15 will charge up rapidly while the voltage across it follows VCC . At VCC≥6V, the capacitor is discharged via an internal current generator and the voltage across it decays linearly. At V15≤3.5V (line saw-tooth peak-to-peak volt-age), phase comparator ”M2” delivers a low conduction period which will gradually increase. The conduction period (Pin 7) will rise until the secondary voltage reaches the value set by potentiometer ”P”. When this occurs, the loop is activated.

The Pin 15 discharge current value is 100μA for a duration of 2μs line frequency. Therefore, ID(AV)=100×2/64=3.1μA Conduction period limitation voltage (Pin 15)TON(LIM)=56μs-16xV15(in μs)

Ok thank you. 👍 

HI. I saw that the remote has worn rubber contacts. Can they be restored?

There are conductive rubber repair kits available but they are very fiddly things and I've never had much luck with them.

I used to solder SMD tact switches onto the keyboard, if it was one of those with gold plated contact lands on the board and not carbon. Pull out the rubber pieces from the rubber mat to make room for them and you have a reliable keyboard with a much better feel.

I take it this Telefunken chassis is ICC5 based ? in view of the TEA2029C, IL14 ?

yes Red-TO BLACK.On pin 15 I have 0 volts without the led flashing. I suspect the transformer eat. Can I test the light bulb by removing bu508 tl31 o interviene la protezione del tea2029?

The feedback loop/s on the ICC5 was a bit strange to say the least, they didn't really like dummy loads as such, without the line stage running you ended up with voltages out of proportion, or in incorrect ratios.

it is not just stuck in stby is it? press and hold the channel up button for about five seconds to check for this as I noted you said the remote control wasn't working properly in a previous post.

edit: how about posting some photos of the chassis?

When I turn it on from the keyboard, high voltage is heard, then the LED goes out.

This could be down to many faults on the ICC5, not necessarily the EHT transformer(lopt), in fact I had very few lopt failures. The faults were/are varied and many on this chassis, not for the faint hearted.

I actually found them ok to deal with but first you really need to understand how they work.

there are many, many, stock faults on these now without seeing it on the bench I could only speculate at best and I must have have repaired a few hundred! of these by now.

I first came across this chassis in the late 80's/early 90's when I persuaded my then boss to buy about 50 or so from a Thorn outlet, they were keen to be shot of them and we got them for a token nominal sum, they even let me see inside of the so called 'gash ones' which I got for free as spares/donors provided we bought the rest that is how keen they were to  be shot of them!

I did manage to repair about 40 odd of them so needless to say I had a long and meaningful relationship with them.

Some of the Telefunken Futura models had a very different software/firmware set up to the Thorn/Ferguson versions , the tuning arrangements were totally different, no osg unless they were of the IMC version, the Nordmende versions were different again, even Hitachi produced both the ICC5 and ICC7 badged up versions which were very different again both in presentation styling and with the operating/tuning system.

Good evening, a whole wiring diagram is possible, not in pieces.thanks.