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Electronics Forum / Electronics / April 2005Digitor 12 volt portable tv for car - mistery
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. 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 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. > i don't know that tv specifically but yes usually a base needs some > drive [quoted text clipped - 4 lines] > > Mark >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  SignaturePlease remove one 's' from my address when replying by email. 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. > >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.) [quoted text clipped - 11 lines] > > - Franc Zabkar > 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 This tv has these ICs: LA7680 and LA7837 and I don't think they provide any drive to the HOT; AT > > 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 [quoted text clipped - 8 lines] > 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 [quoted text clipped - 5 lines] > Regards > James >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 SignaturePlease remove one 's' from my address when replying by email. 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? > >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.) [quoted text clipped - 11 lines] > > - 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 SignaturePlease remove one 's' from my address when replying by email. |
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