Technika 22-880 startup issues

[notallbad]

Re: Technika 22-880 startup issues

OK, PS b/d disconnected from main, no resistor just mains power
PL703
1 0v---------11 0v
2 0v---------12 0v
3 0v---------13 0v
4 11.17v-------14 11.17v
5 5v-----------15 5v
6 5.3v--------16 0v
7 0v ----------17 0v
8 0v--------18 0v
9 0v-----------19 0v
10 0v-------------20 0v

PL706
1 22.1v
2 22.1v
3 0v
4 0v
5 0v
6 0v

[notallbad]

Re: Technika 22-880 startup issues

Main A/V: 17MB60-3.1

S/C across D202 - Pin2 VIN on U23 (RTA8283A)

Needs further investigation but trouble tracing layered pcb.

[notallbad]

Re: Technika 22-880 startup issues

Erm, perhaps its not a diode afterall, but what is it? It reads S.C in-circuit so perhaps just a zero ohm jumper resistor??? But usually they have a '0' printed on them, but not this one.

Its the 3rd SMD down on the immediate left (the black one)to U23 located near the top of the board.

[notallbad]

Re: Technika 22-880 startup issues

Just to be sure I haven't overlooked something I have gone back to the PS.

With just power to the PS b/d I get the first reading and the second reading, in brackets, is with a 1k resistor between Pin 9 and Pin 17.
PL703
1 - 0v (0v)
2 - 0v (0v)
3 - 0v (0v)
4 - 0v (0v)
5 - 0v (0v)
6 - 0v (0v)
7 12vcc - 11.09v (8.5v-10v)
8 12vcc - 11.09v (8.5v-10.2v)
9 +5v_vcc - 4.97v (0.6v-2.2v)
10 +5v_vcc - 4.97v (0.8v-2.2v)
11 stby_5v - 5.23v (4.96v-5.03v)
12 - 0v (0v)
13 pwm_dim - 0v (0v)
14 - 0v (0v)
15 bkl_on/off - 0v (0v)
16 - 0v (0v)
17 stby_on/off - 0v (0.6v-2.2v)
18 - 0v (0v)
19 - 0v (0v)
20 - 0v (0v)

PL706
1 24v - 21.9v (20.5v-21.5v)
2 12v_con - 21.9v (20.5v-21.5v)
3 bkl_on/off - 0v (0v)
4 pwm_dim - 0v (0v)
5 - 0v (0v)
6 - 0v (0v)

Without the resistor the voltages are steady readings but with the 1k resistor the voltages all fluctuate.

Appreciate your help.

[notallbad]

Re: Technika 22-880 startup issues

Would appear that I either mis-read the DMM when reading Pin 11 - stby_5v as it is actually only reading 0.5v, NOT 5.23v.

Either something has now failed or I was reading it wrong everytime, which is possible but find it hard to believe as I have taken the reading so many times.

Well anyway, what is likely to cause this?

[notallbad]

Re: Technika 22-880 startup issues

Tracing back PL703 Pin 11 Stby_5v it goes back to a 3 leg, I think transistor, Q713, it has 1F printed on it. In the photo its located in the middle just below the 2 smd light brown caps.

Top left leg - reads a dropping voltage to below 0.5v
Top right leg - reads a steady 5.49v
Bottom leg - reads a steady 11.07v

Is this the transistor itself at fault as there is not anything else connected to this leg and the voltage is dropping at a rapid and steady rate. Internal leakage?

[notallbad]

Re: Technika 22-880 startup issues

Is it a SOT23 BC847B SMD NPN General Purpose Transistor?

[notallbad]

Re: Technika 22-880 startup issues

Testing in-circuit with a DMM in diode setting it gives different results to other '1F' trans on the board and not what would be expected.

So guess I'll have to source a replacement and go from there. The only concern I have is removing the existing and re-soldering the new without causing any damage to the board.

[notallbad]

Re: Technika 22-880 startup issues

Might just try a BC547 or a BC547B as a temporary measure and replace later if and when I get it fully working.

[notallbad]

Re: Technika 22-880 startup issues

Anyone know the difference between the BC547, BC547B, C etc...

Thanks

[tom66]

Re: Technika 22-880 startup issues

Different voltage ratings, usually, if not, then different gain parameters.

[notallbad]

Re: Technika 22-880 startup issues

By the looks of it I can remove the SMD transistor and use a T0-92 package transistor (on component side of the board) utilising the board holes that exist for a transistor Q714 that connects to all the same tracks.

[tom66]

Re: Technika 22-880 startup issues

That should be fine, I have done that before with Vestel which used SMD diode but had through hole pads, I just used the through hole pads as they were available.

[notallbad]

Re: Technika 22-880 startup issues

Cheers, and would a BC547 be fine?

[tom66]

Re: Technika 22-880 startup issues

A BC547B would work. A BC547 -might- work, but you'd need to take a chance unless you could analyse the circuit carefully to understand how it works.

[notallbad]

Re: Technika 22-880 startup issues

Thanks, shall see if I have a 'B' first.

[notallbad]

Re: Technika 22-880 startup issues

Using a BC547 TO-92 has brought the 5V_Stby back but still no go.

[notallbad]

Re: Technika 22-880 startup issues

Found Q200 on main A/V, its either a FDC642 or a FDC604P, can't determine which one from the SM but its a PowerTrench MOSFET either way.

Between Pins 3(Gate) and 4(Source) reads 32kOhms, on diode test no reading with probes both ways.
However, Pins 4 to 1,2,5 and 6 (Drain) shows S.C, 0 ohms.
And Pins 4,1,2,5,6 show S.C to CN706 Pins 12v_stby and 12v_vcc.
The main a/v board is disconnected from the PS b/d and other boards.

With boards connected and powered
5.4v on Gate
11v on Source and Drain


On checking the Mosfet again there does not appear to be continuity between Pins 4 to 1,2,5 and 6.

I would expect continuity when its powered, isn't that what it does? As the name 'Gate' suggests, allows Source voltage across to Drain. But would think it would be O.C, well have high resistance, when powered off.

[asas]

Re: Technika 22-880 startup issues

Hello,
notallbad, did you solve this fault?
I have a similar fault on a 17PW05-3 PSU (Toshiba 22EL833G): hard to start and low voltage!
12V is 11,27V
24V is 22,99V
(when the tv is on).

Any tip will be very appreciated.
Thanks.