No negative voltages on Shuruthi filter board

Hi there,

I’ve had a look at some of the other threads on this. but I can’t seem to find an answer that fits my problem.

All positive voltages measure fine, and 7805 reads 5/0/8.25, wheras 7905 reads
0 - 0
1 - 0.3

    • 0

I’ve tried reading pin 5 of LT1504 and it also sits at 0.3.

C3 reads 1.3 at the pin closest to the PSU and 0.3 on the futher away. I do have the optional Tantalum in place and have kinda hit a wall here. Sorry if this is an obvious thing, but this is my first real foray into DIY electronics.

Thanks

Please send a photo of your board.

Sorry for the slow reply and thanks for your quick one!

I’ll snap a few pics now and upload them.

Hopefully this is enough

Are you sure that the polarity of C1 is correct?

Yeah, definitely

Send me a private message with your address, I’ll send you another LT1054. Can’t see anything else.

Awesome, thanks. Is it definitely that do you think? I did notice it got very hot first time I tried it.

You’ve probably blown it. Which might be a hint that something else is wrong with your circuit… Have you checked for shorts between adjacent pins of the 7905?

Pretty certain there isn’t. I’ll go through it thoroughly tonight to double check, but the fact there’s slightly different readings on each pin would make me think it’s ok.

How would I have blown the LT1054 out of interest if most other parts seem ok? I did notice it got quite hot on first trial.

ESD discharge is a possibility - though an unlikely one.

Hey,

sorry for the slow reply, the piece arrived at my work and no one thought to tell me about it. Finally got it today, so have swapped it over and the same issue still stands. All + values are fine an no negatives. I can’t work it out, all soldering seems fine and all orientations have been double checked.

Can you post another set of clearer photo of the area around IC1? And the other side too.

Lemme know if you need to see anything else.

Maybe add more solder on all joints. And check C3.

Maybe check continuity at all traces around ic1

Added more solder and still the same. 3 measures 0.3v and 0v

What do you mean by continuty of races qp?

Sorry, redid C3 and it measure 1.3/4v (varying slightly) and 0.3v.

I was wondering if C3 was by mistake a 100nF (104) cap instead of 10pF (100).

Had to desolder it to check, the print was on IC1 side. It’s definitely 10pF