I have added a few more pics. Multimeter proves output values, hope they are of use.

 

Your attached files were too large, it will slow down the connection of forum, before you upload them you can compress them to 800x600 or 1024x768 for the clear picture, if you use the cellphone then you can install a compress app, thank you.

 

Scott I've taken down all but two pics, is that ok.

 

Scott I've taken down all but two pics, is that ok.

What we care about is not how many pics, is the files size of pic, all we know are the resolution as 800x600 or 1024x768, they can keep the small file size and clear picture, if you need then you can upload more resolution, the situation is when the same page have many pics and own the big size, then they will slow down the speed of website and will stop the member who trying to help.

If you want to upload a big pics, the important thing is does that really necessary or unnecessary.

 

Glad I could help with the missed cap connection. Sorry it wasn't the magic solution to your problem.

I like to use small pieces of solid core wire for my breadboard connection, utilizing the board's bus bars as much as possible. I feel it makes for a neater layout, which encourages correct placement of components and makes troubleshooting easier.

I think we can narrow your problem down to either the transformer or the bridge rectifier. Your wiring seems to be okay, and I have used 78xx and 79xx regulators right out of the bin with no problems as far as non-working or "dud" parts. Besides, you have tried the old solving by substitution method already.

Hope you get it going soon.

 

Hi Allvol, thanks for your reply. Think I've scared everyone else away with that messy breadboard. Only have a selection of those type of hook up wires, good for quick builds not presentation. When I started this project I got four W005M bridge rectifiers, have tried all four with same result so I think I can rule it out. Have seen transformers that specify no load characteristics, might buy one that will allow for around 20v at vin instead of 27, its the only solution I can see.
Need to get sorted soon dragging on a bit, anyway thanks again.

 

Can you meaure the voltage at the input to the regulators?

 

Hi kubeek, here's pics showing voltage regs input, also included second meter to show output.

 

Have you tried putting the electrolytic output cap right across the regulator?

 

Moved caps across both regulators and still no change. The caps in circuit aren't most expensive so I tried a better brand, just across 7912 but no difference. I also added an extra 10mf on output but again no difference. Would a greater increase in output capacitance be able to reduce voltage?

 

I don´t think this is about reducing voltage per se, the regulator is most likely oscillating. That could be cured with proper input and output caps. You coud try measuring the AC voltage on the output, that might give a clue on what is going on, if you dont happen to have an oscilloscope.

 

Hi kubeek, I scoped the ac signal at the bridge rec and the wave form isn't perfect, tops are flat, im no expert at analysing, let you decide. The dc outputs seem ok no major distortion. Why would oscillation only effect the 7912 reg and not the 7812? Could this be solved with better quality caps?

 

So the output of the 7912 is nice and clean, but at -19V?

 

Both dc outputs are straight lines across the screen as you would expect with a dc signal. + in top half - in bottom half. Same voltages displayed on scope as on meter. Would you expect to see distortion on 7912 signal?

 

I was expecting the 7912 output to oscillate wildly. If it does nothing then I really have no idea why that output is so much off. You might try getting another one from a different source.

 

Kubeek had another look on scope and there doesn't seem to be any distortion on dc signals, both smooth straight lines.
Think I will either lower voltage by using a different transformer, or as you say try regs from different source.
Anyway appreciate your help, if you can think of anything else let me know, thanks.