Frage zu Ulf's Schaltplan! | Posts 16+

Okay, everything seems to be fine now; LED3 lights up as soon as I bridge pins e and c on T3, so it must be related to T3. The exact designation is BC547B. Should I perhaps try a BC547C instead, or would that not make sense?

ckone wrote:

So far, everything seems to be okay; LED3 lights up as soon as I bridge e and c on T3, so it should actually be related to T3. The exact designation is BC547B; perhaps I should try a BC547C instead, or does that not make sense?

Hi.

Try it out, if the voltage measured between points B and E on T3 is approximately 0.5 to 0.6 volts.
If not, check if the K-line is supplying 12 volts (if not, fix this issue).
and if so, check where the current is being lost on its way through R12 and D7 to T3. Is there a short circuit in the area of R13/VR2?

You can test transistor 3 by connecting a 10 kOhm resistor between the base and the positive voltage. The transistor should then start conducting. You can then increase the resistance. If it fails to conduct before 150 kOhm, the current gain of the BC547 is not sufficient. A C-type transistor might help, as its DC current gain varies between 75 and 900.
Otherwise, use Darlingten BC879 (note the different pin configuration).

'Strangely enough, I'm not getting 12V on the K-line.'
Hmm... The resistance across VR1 and R9 is 6k ohms when VR1 is in the middle position.
I've checked everything again; I have 8.5V on line K and 8.9V between VR1 and R9, so the problem must be somewhere in that area!

ckone wrote:

I measured 8.5V on K-Line and 8.9V between VR1 and R19;

there's definitely a problem somewhere!}

Hi.

If you input 12 volts and observe a voltage drop of approximately 3 volts across a 10-ohm resistor, a current of 300mA is flowing, and resistor R19 must dissipate about 1 watt as heat.
In these cases, the standard electronic components become extremely hot or start emitting smoke.
Did you perhaps install a resistor with a value of 100 ohms instead of 10 ohms for R19?

Oh sorry, I meant not R19 but R9, .

On the L-line, I'm also only getting 8.7V!

'Voltage across the collector resistors? I doubt it. What kind of measuring instrument are you using? An old-fashioned moving-coil voltmeter from your grandpa's drawer? With an internal resistance of 10 kOhms, you'll get measurement errors like that. That would also explain a lot of other things. A high-impedance digital voltmeter would be useful.'

I have a high-impedance digital voltmeter!
That doesn't solve my problem that I only have about 8.5V on the K and L lines. Something is wrong; I'm getting 11.8V going into resistor R6a. I simply don't understand this voltage drop!

It's simple. Systematically disconnect the load. Once only the 1 kΩ resistor is connected, you will have 12V and also identify your fault.
If you have NetMeeting, please send me a private message.

Adapter Status 0: Found and ready!

Thank you very much for your help; I managed to get it working now.
I would especially like to thank AndyO; without your help, I would never have managed it!

The pinout of the BC547 is as follows:

http://andreas.oppel.bei.t-online.de/Bilder/BC547.jpg

P.S. The pin assignments for the optional BC879 (for use with the T3) are as follows: E-C-B.