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Old 8th Sep 2019, 3:53 pm   #1
Vectamart
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Default Philips KT4 Matchline model V6820

This was our main set for many years. We bought it new back in 1985 but retired it in favour of a larger set about 10 years ago, since when it has been stored alongside my vintage TV collection. This afternoon, I decided to run it up and discovered that it is no longer able to store user settings or channels.

My first thought was that the 2.4V backup battery needed replacing. However, I cannot for the life of me find it! Does anyone know precisely where it is located in this model? I have a System 4 manual but the board featured is quite different to the one fitted in my set.

Thanks in advance.
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Old 8th Sep 2019, 5:07 pm   #2
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Default Re: Philips KT4 Matchline model V6820

I think it has a TRDIV tuning system, without a battery.
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Old 8th Sep 2019, 7:55 pm   #3
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Default Re: Philips KT4 Matchline model V6820

Quote:
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I think it has a TRDIV tuning system, without a battery.
Yes that's right. I can't remember if it uses an EAROM or an EEPROM. As I recall (it's a long time ago) the memory is on a thick-film module. I think EAROMS had a finite life......
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Old 8th Sep 2019, 8:00 pm   #4
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Default Re: Philips KT4 Matchline model V6820

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Originally Posted by Vectamart View Post
I have a System 4 manual but the board featured is quite different to the one fitted in my set.

Thanks in advance.
There are a few variants for the tuning system. One is TRDIV(Tuning Remote Digital)
and VST (Voltage Synthesis Tuning). There may have been a simple TRD as well. TRD didn't use a back-up battery (as mentioned in the above post), VST did.
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Old 9th Sep 2019, 1:43 am   #5
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Default Re: Philips KT4 Matchline model V6820

EAROMs have a finite life but I think they also need an auxilary supply. If that's a bit down, they may not work as well.
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Old 10th Sep 2019, 1:03 am   #6
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Default Re: Philips KT4 Matchline model V6820

I have had this problem on a Thorn Tx100 recently. Haven't got around to investigating it yet but after reading the above, I hope it isn't an EAROM!

I have a KT4 stored away that I picked off the street years ago. Unfortunately I cannot recall if it has a battery, (I know the later CP90 and CP100 did.)

ISTR a green bar sweeping across the screen during tuning seek, this was an early sort of OSD I suppose. Does yours do this too?
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Old 10th Sep 2019, 9:04 am   #7
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Default Re: Philips KT4 Matchline model V6820

The green bar was only used in the VST version, I think. In that case it would have a battery.
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Old 11th Sep 2019, 6:03 pm   #8
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Default Re: Philips KT4 Matchline model V6820

Thanks for all the advice. There are a couple of thick film units so presumably, one of these is faulty. However, I would have thought that they would still require some sort of auxiliary or backup power.
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Old 11th Sep 2019, 7:50 pm   #9
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Default Re: Philips KT4 Matchline model V6820

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Originally Posted by Vectamart View Post
Thanks for all the advice. There are a couple of thick film units so presumably, one of these is faulty. However, I would have thought that they would still require some sort of auxiliary or backup power.
No....if it's an EPROM, (Electrically Programmable Read Only Memory), EEPROM, (Electrically Erasable Programmable Read Only Memory), EAROM, (Electrically Alterable Read Only Memory) it won't have a back-up battery. These are referred to as Non-Volatile Memories (NVM)...they don't lose their content in the absence of a supply.

The simpler VST system only uses RAM which does lose content when power is removed so some form of back-up power is required (battery or supercap).

I never quite understood the EAROM. I gather that it uses some form of internal capacitance charge to maintain memory and as long as it is powered up and used fairly regularly (in a TV it would be) then it will maintain memory. However if the set lays idle for years then eventually it will lose its charge and fail. I don't think it recovers.

Maybe others can enlighten!
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Old 11th Sep 2019, 11:03 pm   #10
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Default Re: Philips KT4 Matchline model V6820

My parents Philips CTX lost it's ability to remember channels after many years of use. I remember my Mum let the technicians where she worked have a look at it & they managed to sort it out but it stopped remembering after a few years.
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Old 11th Sep 2019, 11:23 pm   #11
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Default Re: Philips KT4 Matchline model V6820

is it the EAROMS that use a high voltage (eg 30V) to write, often derived from a little charge pump? If so, and I'm no expert on vintage philips tvs, might the converter capacitor(s) be duff?
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Old 12th Sep 2019, 8:05 am   #12
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Default Re: Philips KT4 Matchline model V6820

EPROM, EAROM and EEPROM including Flash all use the same basic mechanism for storing data namely a floating gate MOSFET. Effectively, each storage cell has a capacitor and a FET that is switched on or off by the charge stored in the capacitor.
The above types of PROM vary in the way that the devices are erased, how the storage cells are addressed for reading / writing and erasing and the requirement for additional power supply rails.
Flash is the current state of the art of EEPROM technology and balances the conflicting requirements of write /erase cycle endurance and storage capacity by storing 1, 2 or 3 bits of data per cell. Multi-level cells store one of 4 or 8 different voltage levels per cell, are less reliable than single level cells and require sophisticated error correction and wear levelling algorithms to be usable.

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Old 12th Sep 2019, 12:46 pm   #13
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Default Re: Philips KT4 Matchline model V6820

The TRD IV system did have some thick-film units that gave trouble. They were just a replacement item back in the day. Don't think you could easily get inside one.
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