5 volts regulator

[michel49]

A friend gave me a failed PRO where the 5 volts regulator has fried; where I could find a replacement part or is it possible to fit a "standard" 7805 ?

[jhsa]

Here

http://www.digikey.de/product-detail/en ... mt=b&pdv=c

João

[MikeB]

To confirm, the existing part is "OKI-78SR-5/1.5-W36-C".
You could fit a "standard" 7805, but you will find the total current draw will be higher as it will be (much) less efficient.

Mike.

[michel49]

Thank you JHSA

@MikeB

well, I prefer a switching one, I'm afraid a 7805 give too much heat

MP

[jhsa]

That's correct. You woukd need a heatsink I believe..

João

[michel49]

There is something strange: I tested the regulator on the bench with a 5 ohm load and it s OK...after that I removed the mainboard from the case and powered it with my 5 volts power bench: it works...where is the issue since I got just 2 volts at the output of the 5 volts reg. when I received the Tx ?

MP

[jhsa]

Is that the radio from babz? You offered help to solder on the other thread?
If so, I already said on the other thread that the problem IS NOT the regulator. And you have just confirmed that. I have already told you what the issue is on the other forum
If that is the same radio, THERE IS A SHORTED COMPONENT ON THE MAINBOARD. probably D1, or one of the caps. And that is on the 12V line BEFORE THE 5V REGULATOR.

And here is a quote of my post on RCGroups:

R9 is on the RF board, but it should be fine as you have voltage on D2.
Your problem is a short circuit on the mainboard according to your measurements..
The RF board SHOULD be OK, if they are correct.

I already asked you to measure R9 and FU1, but you ignored it.. Anyway, if any of them was broken I think you wouldn't even see the "Ready Light"..~

You just need help to remove parts.. The problem is diagnosed

Possible damaged parts (See Attached Picture):

1) 5V regulator
2) D1
3) C67
4) C44

João

EDIT: It could be any of them, but my bet goes to D1

Measure the resistance from the right pad of the regulator to ground (or across D1). You will see that there is a short to ground..


João

EDIT: I said on a later post that probably the problem is not the regulator..

[michel49]

Thanks JHSA, issue fixed, R9 was guilty, that resistor is a headache : when I tested it with my multimeter I get around 0 ohm, but the voltage at the input of the 5 V regulator was 4 volts...
It appears the very little current of the ohmmeter give a false measure, with the power ON, maybe 200-300 mAH the value of R9 increase...

MP

[jhsa]

hard to believe, as Babz reported on the other forum a short circuit on the 12V line to ground, also measured with his ohmmeter. That made me think the fault was on the mainboard, and I'm still not convinced. But maybe he gave me the wrong measurement. Anyway, If R9 was damaged, you wouldn't see the "Ready light" ON. He said that this LED was ON.
The value of R9 will increase when the current start approaching 500mA, that is normal, but that radio should not take any close to that value. I believe that 300mA is a bit too much..
Again, what makes you think that R9 is broken? and what did you do to fix it? Measure it with the power OFF. it's value should be close to 0 ohms. Please post the result here..

João