OMG, Another Correction.
I can't edit the original now after 30 mins of posting.
The base of M.N. and Q701(El3-40) emitter..... update:
They are connected together. Tested via continuity test.
They aren't connected directly to ground as it will beep for a small amount of time then O.L. so presume capacitor or diode kicking in?
I can't edit the original now after 30 mins of posting.
The base of M.N. and Q701(El3-40) emitter..... update:
They are connected together. Tested via continuity test.
They aren't connected directly to ground as it will beep for a small amount of time then O.L. so presume capacitor or diode kicking in?
Ok ,so i was initially correct about q701 q702 interconnections.Q702 base gets 5 volts from processor ,so i think processor is trying to turn on radio or at least supply power to face plate. MN marked component must be cpu reset ic ,which i have mentioned earlier ,found one with matching pinout - pin1 you painted as gnd , pin 2 as output to somewhere tape ,and pin3 (single pin on that side) is vcc 5V .Face plate looks like not shorting power ,so we can test supply with resistors .
So now i think q702 is broken ,or trace bethween collector of q702 and base q701. Q701 is a power switch ,gets 5v input in emitter (pnp) from ba ic ,but base is not getting ground ,so its output to faceplate is 0 volts .
Test1 - try to connect resistor 1k from Q701 base to gnd and measure what then will output to faceplate (must be 5v) .If not ,then short collector and emitter through 10ohms of q701 .
So now i think q702 is broken ,or trace bethween collector of q702 and base q701. Q701 is a power switch ,gets 5v input in emitter (pnp) from ba ic ,but base is not getting ground ,so its output to faceplate is 0 volts .
Test1 - try to connect resistor 1k from Q701 base to gnd and measure what then will output to faceplate (must be 5v) .If not ,then short collector and emitter through 10ohms of q701 .
Yes. Test1 has 5v at the on/off switch. It didn't switch on when I pushed it but may need to be put back together?
If this is the solution, can I just solder the resistor in... to avoid smd soldering
So you tried with 1k resistor from base to gnd ant then output 5v appears ,this means q701 pnp is good .Now the same can be repeated ,but now resistor bethween q702 collector and gnd(we will check trace continuity). If 5v appears too ,then need to replace Q702 26 npn digital transistor .Resistor as temporary solution is not good ,because LC ic will always have 5v and may not reset or simply not communicate with cpu ,power-on sequence may be important .Try to desolder that q702 by adding some solder at its pins ,then heat one side ,then other ,and try lifting up one ,then another side ,also mostly smd components are glued before soldering on factory ,so this hardens desoldering a bit .
As alternative you can try to add additional npn transistor not smd ,with 2 additional resistors for it ,and connect it in parallel to existing q702 with small wires .Both resistors can be 47k(values not critical,from 10k to 100k should work),from base to emitter and from base to existing smd base.Transistor-any small signal npn you have ,may be 2n2222 ,bc548 ,2n5551, 2sc1815 ,2sc945 ,or different ,not critical in this case .Also you can try to find similar transistor smd ,marked 26 ,and solder it on top of existing 26 ,and then solder pin by pin,without removing old one (its not shorted,just always not passing current).
As alternative you can try to add additional npn transistor not smd
,with 2 additional resistors for it ,and connect it in parallel to existing q702 with small wires .Both resistors can be 47k(values not critical,from 10k to 100k should work),from base to emitter and from base to existing smd base.Transistor-any small signal npn you have ,may be 2n2222 ,bc548 ,2n5551, 2sc1815 ,2sc945 ,or different ,not critical in this case .Also you can try to find similar transistor smd ,marked 26 ,and solder it on top of existing 26 ,and then solder pin by pin,without removing old one (its not shorted,just always not passing current).
I have a C2785 transistor - quick google says it is NPN the rest I see in my spare parts are PNP so hopefully this will be ok
It has the pins marked on the board.
It looks like it has had better days so will test it first - more googling.
12:00am here so I'm off to bed for now.
Thanks ximikas for your hard work.
Let me know when you start getting weary of this so I will have to try and speed things up.
Wife thinks kids are more important than this so I have to sneak off every now and then to do more tests.
It has the pins marked on the board.
It looks like it has had better days so will test it first - more googling.
12:00am here so I'm off to bed for now.
Thanks ximikas for your hard work.
Let me know when you start getting weary of this so I will have to try and speed things up.
Wife thinks kids are more important than this so I have to sneak off every now and then to do more tests.
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Looks correct . I have found some pdf for cpu , UPD78096 ,but they contains lots of information .How much pins has your cpu and in which package ? Yours is from μPD78098 subseries. Need to determine power supply ,external oscilator pins ,maybe something interesting else . Link to cpu datasheet UPD78098 Datasheet(PDF) - NEC
20 pins on each side so 80pins total.
Possibly this one?
UPD78094_4562999.PDF Datasheet Download --- IC-ON-LINE
The Q702 base leads to pin13
But in the diagram pin 68 is VDD. On the board it connects to that silver thing 6.2ekss7gt - presume a crystal?
So possibly not correct.
UPDATE ON piggybacking the transistor:
It is so small and fiddly.
still on step one. Just trying to solder small wires to the ends of the new one. I've soldered pins together and wires together - started again and the joins are week. try to strengthen them and the wire falls off ....ongoing.
Possibly this one?
UPD78094_4562999.PDF Datasheet Download --- IC-ON-LINE
The Q702 base leads to pin13
But in the diagram pin 68 is VDD. On the board it connects to that silver thing 6.2ekss7gt - presume a crystal?
So possibly not correct.
UPDATE ON piggybacking the transistor:
It is so small and fiddly.
still on step one. Just trying to solder small wires to the ends of the new one. I've soldered pins together and wires together - started again and the joins are week. try to strengthen them and the wire falls off
....ongoing.Tried to solder on my frankenstein contraption and it wouldn't take.
I walked away for a time, as this is the stage when I caused issues with the TV board, i.e. trying to force it. I will try again today.
I don't have the correct tools. There are capacitors making hard angles, I need a smaller tip, thinner solder and I need a magnifier. lol not much.
...so don't want to wreck as we have come so far ...will get there.
I walked away for a time, as this is the stage when I caused issues with the TV board, i.e. trying to force it. I will try again today.
I don't have the correct tools. There are capacitors making hard angles, I need a smaller tip, thinner solder and I need a magnifier. lol not much.
...so don't want to wreck as we have come so far
...will get there.
Nice to see some progress,even negative . Looks like 2622 base shorted to gnd, thus your new transistor can't turn on.Try to measure resistance bethween 26 marked transistor pin1 and gnd. Or you incorrectly soldered c2785,and it gets 5v to base from 26 collector,and thus shorting 26 base to gnd,instaef of shorting 26 collector to gnd.
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43.6k ohms between Base and Emitter on the 2622
I have double checked the new device is connected to the right pins seems ok.
Continuity between all 2622 pins is open - thought I may have soldered B and E together. I did at first but removed it.
Possibly I need to check the device. Not sure how.
I have double checked the new device is connected to the right pins seems ok.
Continuity between all 2622 pins is open - thought I may have soldered B and E together. I did at first but removed it.
Possibly I need to check the device. Not sure how.
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