Digitor 12 volt portable tv for car - mistery

[alitonto]

Digitor tv model G-7200 pcb 031B
The tv does not start; there is 10.47 volt on the collector of the HOT
(BU407)whch is straight from the FBT and there isn't any volts on the
base.
Checking the circuit board I see the base is connected via a resistor
to ground and via a high voltage ceramic cap back to the emmiter line
of the HOT. That is it.
Shouldn't somethingelse be feeding the base or do these 12 volt tvs
work differently?
Any thoughts will be very much appreciated.
A.T.

 

[Mark]

i don't know that tv specifically but yes usually a base needs some
drive

maybe you have the basing mixed up

are you sure you don'e have the base and emitter mixed up?

Mark

 

[alitonto]

Yes I am quite sure because the emitter pin is directy soldered to the
ground of the circuit board.
I am starting to suspect that someone has tried to repair this and
removed some wire coming directly from an IC.
Anyone got schematics on this TV can they please tell me where the
drive to this HOT should be coming from. (Eg. a transistor or IC etc.)
It will make this easier.
Thanks a lot.
A.T.

 

[Franc Zabkar]

Anyone got schematics on this TV can they please tell me where the
drive to this HOT should be coming from. (Eg. a transistor or IC etc.)
It will make this easier.

Have you tried contacting Dick Smith spare parts for a service manual?

Phone: 1300 660 054
Email: service at dse dot com dot au
spares at dse dot com dot au

Otherwise post the part numbers of the major ICs. Someone may be able
to locate a datasheet with an application diagram that matches your
set. I'd be looking for a multi-pin jungle IC, eg 40-pin or 64-pin.


- Franc Zabkar

 

[AliTonto]

Thanks for the info as I couln't find who makes these tvs;
I will follow up for a schematic with DSE but in the meantime I would
like to know if the voltage at the collector of the HOT for these
portable 12v tvs in general should be 110-130 as the bigger ones. (I
have measured 10.84 volts which is coming straight from the FBT.
Thanks A.T.

 

[James]

Thanks for the info as I couln't find who makes these tvs;
I will follow up for a schematic with DSE but in the meantime I would
like to know if the voltage at the collector of the HOT for these
portable 12v tvs in general should be 110-130 as the bigger ones. (I
have measured 10.84 volts which is coming straight from the FBT.
Thanks A.T.

<SNIP>

Some time back there were a number of different branded small 12v TVs using
the same chassis. I cant recall how big they were exactly but around 6-8".
The entire TV ran on 10V, when using the 12VDC supply it first passed
through a 10V linear regulator, when using on 240VAC just used a 12V
transformer then through the same reg. The most unreliable part of them was
the regulator and a switchmode equivlent of the genuine encapsulated part
used to be available from GB telespares. That said I do recall one time
having one of these chassis fail to fire up the horizontal and it did turn
out to be the jungle / sync IC.

Regards
James

 

[alitonto]

This tv has these ICs: LA7680 and LA7837 and I don't think they provide
any drive to the HOT;
AT

 

[Franc Zabkar]

This tv has these ICs: LA7680 and LA7837 and I don't think they provide
any drive to the HOT;

LA7837 is the vertical output, LA7680 is your jungle IC. Pin 27 of the
LA7680 is the horizontal output pin. A datasheet and application
circuit is available from http://www.bdent.com.


- Franc Zabkar

 

[alitonto]

Special thanks to Frank for assisting me realise that I was looking for
the wrong IC info; I didn't think that the LA7680 on the tv had plenti
of legs; for some reason I was convinced it was only 24 pns.
I have now obtained the correct datasheet.
Great help thanks
A.T. by the way how do I remove an S from your email address?

 

[Franc Zabkar]

A.T. by the way how do I remove an S from your email address?

My address, like those of many others, has been munged as an antispam
measure to prevent automatic harvesting by spambots. When you reply to
me by email, you need to locate my address in your headers and
manually correct it. I suggest you modify your own hotmail address to
avoid being deluged by spam.


- Franc Zabkar