Low supply voltage IC6

[Badboydas]

Hi
Just started this project, everything is fine until IC5 (NE555N) is socketed then the output of IC2(78l05) drops to between 2.5-3.5v depending on pulse width and frequency pots. IC6 socket pin 7 +5v then only has the same output of the 78l05. TP1 down to -0.34v and upto -1.78v and centered -0.73v IC5 has frequency of between 943hz-2173hz.
Any and all help greatly appreciated.
cheers

[mickstv]

Have you got your multimeter connected correctly. The negative lead has to go to plus 12 volts or pin 4,8 of IC5 (NE555N). This is because the + and - 5 volt rail is centred on +12volts.

[Badboydas]

Hi mickstv
Yes ground is being taken off positive of regulated power supply.
In the previous post I forgot to mention I have only built upto 5534, I Know this is something really simple
thanks for your help

[mickstv]

Hi Badboydas, What voltage are you getting on the input to the 78L05, and are you actually running it from 12 volts or are you using a lower voltage.

[Badboydas]

HI mickstv Power supply set to 12v, with IC5(ne555n) out of circuit the input of 78l05 is 12v, with 555 in thats when the volts drops.
cheers

[Badboydas]

Not sure if this will help, but maybe you`ll spot something that I`m missing

[mickstv]

It might pay to add D8 near the IC5. Have you measured the voltage between +12 volts and the input pin of the 78L05 (pin3 and pin2) what is it ?

Also R37 and C11 are used to sync the power supply to the TX pulse, disconnect/desolder and remove one side of R37, and check you +5volt rail.

[Badboydas]

Cheers for your help mickstv, C3 22uf was reading 180nf once replaced all is fine. Lets hope it goes a bit smoother from here.
cheers

[mickstv]

Good to hear you've got it working ok.


Cheers
Mick