I finished installing and connecting up the boards etc inside the case today, wish i had tested it better but as it had seemed fine outside it's case i didn't bother, first time too, doh! 
Anyway the PSU took a hit, seems to have fried a couple of diodes at least but i'm stumped as to how it happened. The wiring checked out, i checked it over at least 8 times before i powered it up.
The affected diodes are clearly shorted and cooked but i dont see any other visible damage.
I have tested the obvious and now i'm stumped!
I measure a dead short between PG+ and PG- on both amp boards with the PSU totally disconnected, shurely this is not right! does this mean i have also somehow fried both chips? I've taken some pic's, can some kind soul please have a look and give me some pointers as to what went wrong.
Anyway the PSU took a hit, seems to have fried a couple of diodes at least but i'm stumped as to how it happened. The wiring checked out, i checked it over at least 8 times before i powered it up.
The affected diodes are clearly shorted and cooked but i dont see any other visible damage.
I have tested the obvious and now i'm stumped!
I measure a dead short between PG+ and PG- on both amp boards with the PSU totally disconnected, shurely this is not right! does this mean i have also somehow fried both chips? I've taken some pic's, can some kind soul please have a look and give me some pointers as to what went wrong.
An externally hosted image should be here but it was not working when we last tested it.
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Hi Andrew, I know I should have used the tester again, couldn't find it at the time, took a chance, kicking myself now!
Had visitors and a couple of drams which DID help me, they just left so i'll have a go at the amp tomorrow, probably/hopefully it's a short as you suggest caused by the standoff washers or some such issue. Have to get me some new diodes though at the very least.
I was going to wrap the mains socket in self amalgamating tape (great stuff that)before the lid went on, that'll have to wait a bit now.
Had visitors and a couple of drams which DID help me, they just left so i'll have a go at the amp tomorrow, probably/hopefully it's a short as you suggest caused by the standoff washers or some such issue. Have to get me some new diodes though at the very least.
I was going to wrap the mains socket in self amalgamating tape (great stuff that)before the lid went on, that'll have to wait a bit now.
It annoyed me enough to have another look, it appears that I bridged a track on the left amp board to ground with the brass washer which is a tiny bit wider than the screw head, enough to just land on the very edge of the nearest + track. This is an issue with this board, there is a small copper ring where the screw head lands but it is separated from the + track by a gap of slightly less than 1mm. If I had not bothered fitting washers or used nylon standoffs, it wouldn't have happened!
Anyway with the boards now unscrewed I get the following readings from both amp boards.
PG+ to ground = total short
PG- to ground = total short
The left channel did read a short between V- and ground before I unscrewed it's board, it now seems ok, well open circuit anyway?
Pity I did not think to take these reading before I messed up, doh!
Anyway I can't test the chips so i'll have to get a set of PSU diodes and replace them then start testing all over again. Unless anyone can verify, going by my readings, if the chips are damaged. The amp board readings were taken with the PSU totally disconnected.
Anyway with the boards now unscrewed I get the following readings from both amp boards.
PG+ to ground = total short
PG- to ground = total short
The left channel did read a short between V- and ground before I unscrewed it's board, it now seems ok, well open circuit anyway?
Pity I did not think to take these reading before I messed up, doh!
Anyway I can't test the chips so i'll have to get a set of PSU diodes and replace them then start testing all over again. Unless anyone can verify, going by my readings, if the chips are damaged. The amp board readings were taken with the PSU totally disconnected.
This is a case of my paying attention to detail like using a magnifier to check the tracks and joints etc (my eyes are not as good as they used to be) I checked all connections many times over, then I go and slap some screws with washers on right where they would do damage.
Worst of all, since it seemed fine out of the case and I couldn't find my tester rig I went and plugged it in. An amateur mistake from someone who should and does (normally) know better! Guess how I feel now
Worst of all, since it seemed fine out of the case and I couldn't find my tester rig I went and plugged it in. An amateur mistake from someone who should and does (normally) know better! Guess how I feel now
This is madness! If I can help someone else avoid this happening to them it would be something though I suppose.
The fuse was a 3A slow blow, it blew but obviously too slowly!
I just spent over an hour ordering parts from farnell! I hate their website so i have not bought from them in years. I finally ordered more than I need because they have a minimum £20 order below which they charge £5 handling. After finally finding everything and filling out the order for 10 x MUR860 2 x LM3886TF 10 x 3A slow blow and 10 x 3A standard fuses (min order of 10) I find that their website does not accept my maestro card or paypal!!!
After a half hour phone call they accepted my order, processed the maestro payment, then told me they had a £6 handling fee for phone orders under £30!
I was finally stung for £36.76 and was so hacked off I just meekly said ok, whatever, just let me off this dam phone!
I probably don't need all of that but it will probably all be used at some point, twenty 3A fuses could be handy eh, right!
The fuse was a 3A slow blow, it blew but obviously too slowly!
I just spent over an hour ordering parts from farnell! I hate their website so i have not bought from them in years. I finally ordered more than I need because they have a minimum £20 order below which they charge £5 handling. After finally finding everything and filling out the order for 10 x MUR860 2 x LM3886TF 10 x 3A slow blow and 10 x 3A standard fuses (min order of 10) I find that their website does not accept my maestro card or paypal!!!
After a half hour phone call they accepted my order, processed the maestro payment, then told me they had a £6 handling fee for phone orders under £30!
I was finally stung for £36.76 and was so hacked off I just meekly said ok, whatever, just let me off this dam phone!
I probably don't need all of that but it will probably all be used at some point, twenty 3A fuses could be handy eh, right!
3A & 240Vac is a lot of power handling.
What VA is your transformer?
BTW,
fuses do not save semiconductors.
Correctly sized fuses prevent setting your house on fire.
But diodes can fail to short circuit.
If you overload a diode in a rectifier and that diode fails short circuit, that could send AC to the next stage.
AC will probably destroy the chipamp.
To help prevent this calamity, fuse the Mains input so that an overload shuts the whole thing down and hopefully this happens fast enough that as the diode fails the fuse blows and the chipamp never sees that AC.
A 600VA to 700VA needs a T3A fuse.
A 200VA to 250VA needs a T1A fuse.
A 160VA needs a T800mA
What VA is your transformer?
BTW,
fuses do not save semiconductors.
Correctly sized fuses prevent setting your house on fire.
But diodes can fail to short circuit.
If you overload a diode in a rectifier and that diode fails short circuit, that could send AC to the next stage.
AC will probably destroy the chipamp.
To help prevent this calamity, fuse the Mains input so that an overload shuts the whole thing down and hopefully this happens fast enough that as the diode fails the fuse blows and the chipamp never sees that AC.
A 600VA to 700VA needs a T3A fuse.
A 200VA to 250VA needs a T1A fuse.
A 160VA needs a T800mA
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It's a 300VA so by your guide I used too high a rated fuse! I definitely read a post somewhere by a bloke saying that because of the current in-rush he needed a 2.5 to 3A fuse for that size transformer. He said a smaller fuse would not last very long without soft start.
I found the light bulb tester I made weeks ago in the boiler cupboard today while looking for something else. Doh!
I could not face ordering new diodes only to fit them and then find I needed to order new chips too so they are all now ordered and should be here next Tuesday (hopefully)
I found the light bulb tester I made weeks ago in the boiler cupboard today while looking for something else. Doh!
I could not face ordering new diodes only to fit them and then find I needed to order new chips too so they are all now ordered and should be here next Tuesday (hopefully)
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I'd have ordered just the diodes from RS. OK there would be a handling charge but they wouldn't have cost £36.
Or for fault finding just fit some 1N4001's. Once it's working you can go on to glorious components.
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