varioprop 12s repair

[Les Jones]

I can't tell the specification of a zener diode from a picture. You could either just try it in circuit or measure the voltage across it when passing a range of currents through it. I suggest trying it with 1 mA, 2 mA, 5 mA, 10 mA and 20 mA. For example just use 12 volt power supply and a range of resistor. You do not have to stick exctly to these currents so just use the nearest prefered value resistor to give about these currents. So for example for 1mA the calculated resistor value would be 5.8 K so use a 5.6 K The zener diodes I used mostly in the past were the BZY83 series and there zener voltage was specified at 5 mA. Wait to see what other think about suitable zener diodes for such a low current.

Edit. I have just read your post #60. So now you have 5.3 volts on the emitter of t110 the pulse generator part of the circuit should work unless there are more faults. Do you have an oscilloscope to see if there are pulses on any of the shift register output pins ?

Les.

 

[vari21]

unfortunately no oscilloscope yes i agree with you it should be some fault somewhere.

 

[Les Jones]

I can't think of a way to go any further without access to an oscilloscope. You could check the the multivibrator is working by connecting one of it's outputs (The collector of either transistor.) to the input of an audio amplifier via a capacitor and resistor in series. (Say 100K and a 0.1 uF) You should hear a buzz if it is working. Avery rough mental calculation suggests that it will be about 50 hZ with about a 20:1 mark space ratio. After that a possible way to see if the shift register part was working would be to tap off the output of the output of one stage of the shift register via a buffer stage using CMOS inverters and using the output to drive a model servo. The pot that controls the length of the pulse from that stage of the shift register should cause the servo to move. Have you tried to see if it works with the receiver and servos since getting the 5 volt rail to a sensible value ? From the fault description in your first post it sounds like the transmitter part is probably working as the receiver / servo behaves differently when the transmitter is powered on.

Les.

 

[vari21]

yes i agree i will order an oscilloscope i wanted one since longtime.
while im checking the t104 i break one of it legs so i took it off to replace it the problem i dont have one on stock i need to order one what could repalce t104 bd137 or bd400 what s the suitable one.

 

[vari21]

do you les jones think the bd 137 will be the right t104 replace cause i ve got it on the other working radio ?

 

[vari21]

hello again to everyone hope you doing well, im coming back here i need your lights ,help please with T104 equivalent replacement for this radio.

 

[dr pepper]

Is it a round metal can package, or a plastic one with a bolt hole.

 

[vari21]

hi dr pepper it s it s to126 plastic package i think, i ve uploaded a picture of it also picture of a shematics , it s t104 .

 

[vari21]

it s a plastic one with a bolt hole.

 

[Nigel Goodwin]

do you les jones think the bd 137 will be the right t104 replace cause i ve got it on the other working radio ?

If it's working on the other one, then it should be OK in this one.

However, it's an audio transistor, not an RF one - and it's ft is only 50MHz.

 

[dr pepper]

Just a guess so it might not work, however I remember seing a 27mc transmitter that used a Bd139, the package is the smae, not sure about the pinout.
Maybe you ought to get a cheap component tester, you can get them on ebay for very little.

 

[vari21]

i ve already bought the bd137 and tried it did, nt worked.

 

[Les Jones]

About 4 weeks ago you said that you were ordering an oscilloscope. Has that arrived and have you proved the pulse generator part of the circuit is working ? How have you proved that it not working because of the BD137 and not for some other reason ?

Les.

 

[vari21]

yes is true les jones i did ordered one from china ,but the seller has cancelled my order due to the hygiene crysis i waited for a month anyway.
before when i turn on the radio servos jiggle moves but not responding to the commands.
now when i turn on the radio servos dont moves nothing happen.

 

[dr pepper]

Did you check the data sheets for the original and the Bd137 to make sure they are the same, you might have to 'cack' leg the replacement.

 

[vari21]

to be honest i did nt checked the datasheet ,i ordered the bd137 i thought that it will work but not.i realised after yhat they are 2 different transistors.

 

[dr pepper]

Doesnt mean the Bd137 wont work.
Whats the number of the original again,

 

[vari21]

ok i ve got some measurements,
i set the multimeter on diode, the reference side of the bd400 transistor in front of me the black side were is writted the ref of transistor.

black probe in the middle leg , red probe in the right legsit reads 0.528
black probe on the left leg the red probe on the right leg 0.543
black probe on the middle leg ,red probe on the left leg no reading

 

[Ylli]

So it's an NPN with a E-C-B pinout.

 

[vari21]

yep npn B C E.