Digitor 12 volt portable tv for car - mistery

• • A
  • alitonto
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• posted
  17 years ago
  Sun, Apr 24, 2005 3:23 PM

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.

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• • M
  • Mark
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• posted
  17 years ago
  Sun, Apr 24, 2005 4:34 PM

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

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• • A
  • alitonto
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  17 years ago
  Mon, Apr 25, 2005 8:42 AM

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.
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• • F
  • Franc Zabkar
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  17 years ago
  Tue, Apr 26, 2005 7:16 AM

On 25 Apr 2005 01:42:03 -0700, "alitonto" put finger to keyboard and composed:

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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

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• • A
  • AliTonto
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  17 years ago
  Wed, Apr 27, 2005 4:00 AM

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.

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  • James
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  17 years ago
  Wed, Apr 27, 2005 6:30 AM

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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

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  • alitonto
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  17 years ago
  Thu, Apr 28, 2005 3:30 PM

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

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would

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(I

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using

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6-8".

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them was

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part

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time

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turn

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• • F
  • Franc Zabkar
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  17 years ago
  Thu, Apr 28, 2005 10:31 PM

On 28 Apr 2005 08:30:34 -0700, "alitonto" put finger to keyboard and composed:

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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

formatting link

- Franc Zabkar

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  • alitonto
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  17 years ago
  Fri, Apr 29, 2005 11:34 AM

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 wrote:

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etc.)

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manual?

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• • F
  • Franc Zabkar
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  17 years ago
  Fri, Apr 29, 2005 11:31 PM

On 29 Apr 2005 04:34:16 -0700, "alitonto" put finger to keyboard and composed:

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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

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