Roberts Radio high ampage  Mistake  - Page 1
Forum section: electronics / beginners

author: kungfu-pegasus
author_rank: Newbie
timestamp: May 22, 2015, 06:52:10 am
content: Hi there i have a roberts radio model RFM3 and i changed the polarity of the dc jack to + in middle ad - out side as normal then i plugged in a 1500 Ma 9v charger and it blew the radio somehow as it doesnt power on nowi checkec the orginal charger and it was 500Ma 9v i have taken pictures of board can someone please give me an indicationof what could have blown please the radio does not power through jack or battery terminals anymorecheersalso attached schematics which i found in netPictureshttps://flic.kr/s/aHskbVzKjCp.s i am a total newb but i am wiling to do the work

author: Delta
author_rank: Super Contributor
timestamp: May 22, 2015, 12:09:02 pm
content: You can't "put to much current in", a device will _draw_ whatever current it needs.Looking at the schematic, that's a 3 wire switching jack, so my guess is you've created at short when trying to change the polarity...

author: kungfu-pegasus
author_rank: Newbie
timestamp: May 22, 2015, 12:43:45 pm
content: superb so where do i start guys ?

author: Rerouter
author_rank: Super Contributor
timestamp: May 22, 2015, 12:52:34 pm
content: well your in for a fun time, seeing as the circuit had no diode... (seriously WTF?) first thing i would do is grab a multimeter and make sure that the power inputs when switched on are not shorted together, (e.g. blown cap or chip).diagnosis steps,test that 9V is at the plug before switcihg on, (battery removed, and correct polarity)switch onsee that your voltage is still there, and that it is not heavily pulled downif ok, next up, lift out the potentiometer that connects the lower op amp to the top one, and inject a signal to the top one, see if this gives any response on the output (this will verify is that chip works)if ok, then replace the pot and turn your attention to the bottom op amp,that should be enough to cover you for a while, and install a diode in the positive connection to the board if you can,

author: kungfu-pegasus
author_rank: Newbie
timestamp: May 22, 2015, 01:34:49 pm
content: oh shit did you just speak chinese?

author: BradC
author_rank: Super Contributor
timestamp: May 22, 2015, 01:39:52 pm
content: Quote from: kungfu-pegasus on May 22, 2015, 01:34:49 pmAre you sure you're in the right place?

author: kungfu-pegasus
author_rank: Newbie
timestamp: May 22, 2015, 01:41:21 pm
content: what do you mean i am in newb section and the geezer speaking to me like i am a procan i have it explained to me a bit better i am a total newb for petes sakeand yes i thought i was in right place new section...are u ?

author: rolycat
author_rank: Super Contributor
timestamp: May 22, 2015, 01:54:14 pm
content: A beginner in electronics typically owns at least a multimeter and a soldering iron. If you are such a "total newb" that you don't own either, or understand what a diode, a potentiometer or a capacitor are, you probably won't get far trying to repair a fried radio.Perhaps you could describe your level of experience in a little more detail so that prospective helpers know where to pitch their explanations?

author: madires
author_rank: Super Contributor
timestamp: May 22, 2015, 02:02:33 pm
content: Have you also rewired the switch contact of the DC jack for the battery? If so, how?

author: amyk
author_rank: Super Contributor
timestamp: May 22, 2015, 02:08:31 pm
content: Quote from: rolycat on May 22, 2015, 01:54:14 pmDoes the OP even know what a multimeter is...?Given that he found schematics he should also be able to look up what those terms mean.

author: Wilksey
author_rank: Super Contributor
timestamp: May 22, 2015, 02:31:02 pm
content: Quote from: kungfu-pegasus on May 22, 2015, 01:41:21 pmBasically what he is saying, in layman's terms, is it's buggered, if you don't know one end of a soldering iron to the other then buy a new radio.

author: w2aew
author_rank: Super Contributor
timestamp: May 22, 2015, 02:56:00 pm
content: Quote from: kungfu-pegasus on May 22, 2015, 06:52:10 am

author: radioFlash
author_rank: Regular Contributor
timestamp: May 22, 2015, 05:43:55 pm
content: Quote from: kungfu-pegasus on May 22, 2015, 01:41:21 pmPlease be courteous to someone who has spent time to look at your photos, think about your question, and offer advice for free. If you don't understand what they have said or suggested, courteously say you don't understand and say what your level of experience is. Also, do research on the terms they've used and spend some time to see if you can understand what was suggested (you said you were willing to do the work, right?).

author: Rerouter
author_rank: Super Contributor
timestamp: May 22, 2015, 08:41:36 pm
content: didn't know 22 years old qualified as a geezer, (watch your tongue you young whipper-snapper :p )by cap, i mean capacitor, either a tantalum type, or an electrolytic,http://www.learningaboutelectronics.com/images/How-to-read-a-tantalum-capacitor.pnghttp://upload.wikimedia.org/wikipedia/commons/8/87/Polarity-wet-Al-Elcaps.jpgby potentiometer, at-least based on how the schematic is laid out it would be your volume control knob,This is what i mean by a multimeter:http://www.jaycar.com.au/medias/QM1323ImageMain-300Wx300H?context=bWFzdGVyfGltYWdlc3wyOTU3NHxpbWFnZS9qcGVnfGltYWdlcy9oODYvaGU4Lzg4MTUxOTg3NjUwODYuanBnfGM0YWJhODlhNjc5NTNlMDYwODhmMTU1OGExNWQ5ZjZmZjhkMzIwYWI0Nzk5ODk4ZWNkOWU2YjU1MjUyODdmOTcNothttp://cf.cdn1.zepo.in/upload/product_photos/base/0/18/94/original1.1203731.1.jpgand to cover the only other term i think you may get caught on,http://www.allaboutcircuits.com/vol_3/chpt_3/1.htmlLike wilksey said, the thing is buggered, what i TRIED to help you with was working out what piece of it was buggered, to then replace / repair to get it working,

author: BradC
author_rank: Super Contributor
timestamp: May 24, 2015, 01:15:37 am
content: Quote from: kungfu-pegasus on May 22, 2015, 01:41:21 pmOk then. Take what the gentleman said to you and start dissecting it. When you find a bit you don't understand, punch it into google and see what comes up. That way you can break it down into bits you *can* understand and you'll learn something along the way. The other option is to come back with more questions, but to just say "oh shit did you just speak chinese?" makes you look like a petulant 10 year old who want's to be spoon fed (and they don't get far on this forum).We all started somewhere, but as with life in general, the key is learning to teach yourself. At least these days you have access to a massive on-line library with information at your finger tips.

author: codeboy2k
author_rank: Super Contributor
timestamp: May 24, 2015, 02:47:00 am
content: OP sounds like a fine example of theGoogle generationQuoteGen-G'ers can't think for themselves, even when told how. Rerouter is an exception

author: Skimask
author_rank: Super Contributor
timestamp: May 24, 2015, 03:10:44 am
content: The O/P has left the building.Re-enrolling in Underwater Basket Weaving 101.

author: apelly
author_rank: Unknown
timestamp: May 24, 2015, 04:05:32 am
content: Quote from: BradC on May 24, 2015, 01:15:37 amOr a marketing manager

author: G7PSK
author_rank: Super Contributor
timestamp: May 24, 2015, 08:42:23 am
content: First thing I would do is reverse what you have just done to the power socket, the radio may still work then on the battery, it is quite possible the only thing that you shorted was the power supply, that depends of course on which of the two wires on the power socket you swapped around but if you are lucky it may well be.