Chiarra / Andante blown PSU / burnt board / fuse question
Mar 2, 2004 at 9:42 PM Thread Starter Post #1 of 15

PinkFloyd

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I fitted a couple of polypropelyne "ANSAR Supersound" capacitors in place of the metallised polycarbonate caps that were originally fitted in the Chiara.

I soldered the board back into the enclosure after cleaning the circuit with a toothbrush and isopropyl and inspecting with a magnifying glass.

Connected the PSU to the Chiarra and switched on...... the 2 polarity green LED's lit for a few seconds and then went out, as did the PSU. Both fuses blew and the area around R3 was truly cooked, R3 actually flew into the air a few inches and landed on the carpet
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I phoned Shaun Williams and first off asked him if the caps I had fitted were suitable in the circuit and he said they were. I then explained that the PSU had partly fried and he reckons it could have been a short circuit between the PSU connections on the Chiarra board...... any Chiarra owner will know that the spacing between wires is very close and this is the weakest part of the design....... it was originally designed for an edge connector but is now wired with very little room between +/- V

Anyways...... to cut a long story short......... I inspected every part of the Chiarra for a short and couldn't find one. What is really concerning me is that Shaun said the amp could have been damaged also. If that proves the case I will be extremely peed off!!

Am I correct in assuming that a well designed PSU should "protect" the amp from any damage under short circuit conditions??? ("IF" that's what caused the PSU to fry) The PSU is a write off but the amp doesn't appear "visually" to have been damaged...... I attach a photo.

I'm was in a bit of shock and couldn't quite grasp what happened and quickly packed the amp and PSU into a box and sent it back to Shaun...... god I never thought a PSU blowing could make me feel sick to the pit of my stomach but this has
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My question is (I'll be able to answer it myself when I awake from this nightmare!) if the amp had a short circuit between +/- V should the Andante fusing system have protected it? My other question is (I know the answer but I want to someone to tell me I'm asleep and dreaming!) with 2 fuses in the circuit why the hell did the section over at R3 turn into charcoal?

There is someone else here who experienced a "blackened" R3 but I've been dealt the full blow with a toasted R3. This should not occur in a well designed protection circuit should it?

I'm praying that the Chiarra is OK and hoping the Andante has absorbed all the damage....... I'll report back as soon as Shaun has had a look at the circuits but I'm pretty p*ssed off that more than the fuses "blew"

Comments appreciated.

Here is the pic of the Chiarra "after" the Andante blew. Physically it looks in good health? I won't upload a picture of the Andante until we get to the root of this.

Pinkie. <tongue tied and twisted just an earthbound misfit>

BTW........ what smart arse recommended ANSAR caps?
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PS: The "Rock" is just a bit of Pink snake oil. It's Iron Pyrite (fools gold) and I believe it absorbs nasties like RFI / EMI it possibly fries PSU's too
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crap this has been a bad day amp wise
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Mar 2, 2004 at 9:53 PM Post #2 of 15
mike, sad news for sure!!

the Chiarra looks fine to my eyes, there's no outward sign of damage to that. It's strange that both the fuses blew on the Andante, which backs up Shauns suggestion it's a short between V+/V-. The Andante is a very simple design, and the regulators it uses are output protected at 1.5A to prevent such as this, but the Chiarra will draw far less than that. Whats the role of R3? I presume it's on the Andante??

g
 
Mar 2, 2004 at 9:55 PM Post #3 of 15
Damn, that's really unlucky Mike
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I know how much time and effort you've put into your Chiarra - I hope the amp isn't too badly damaged!

Good luck on getting it back up and running again
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Mar 2, 2004 at 10:19 PM Post #4 of 15
Quote:

Originally posted by guzzler
mike, sad news for sure!!

the Chiarra looks fine to my eyes, there's no outward sign of damage to that. It's strange that both the fuses blew on the Andante, which backs up Shauns suggestion it's a short between V+/V-. The Andante is a very simple design, and the regulators it uses are output protected at 1.5A to prevent such as this, but the Chiarra will draw far less than that. Whats the role of R3? I presume it's on the Andante??

g


I haven't got the schematic to hand Guzzler but I can safely say it's role isn't to self destruct in unison with the fuses
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Yes....... R3 is on the Andante and I'll tell you exactly what it does or doesn't do this time tomorrow. I'm pretty much taken aback atm and just can't believe my baby blew......... let alone the "fact" I sent her to Wales!!!

I shouldn't have posted this but it feels as if a loved one has died
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I felt so bad when the PSU blew........ like "oh god no"
I could say "sod it........ build another one" but every component in that amp had a story to tell. (I feel the white coat brigade approaching in their van)

If the amp is OK I'll be over the moon........... sad to lose the PSU but crap happens.......
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Mike.
 
Mar 2, 2004 at 11:07 PM Post #5 of 15
Quote:

Originally posted by PinkFloyd
sad to lose the PSU but crap happens.......
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thing is with power supplies, brown stuff often hits the fan again unless corrective measures are taken. Power supplies very rarely just go pop without some error further down the line. The fact that both fuses have blown and R3, by all accounts, is charred suggests to me that it would be unwise to plug 240Vac back into it until you've got a good idea of what happened and have taken some action toward fixing it. Losing a power supply is one thing, but taking 240V in the arm is quite another
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g
 
Mar 2, 2004 at 11:37 PM Post #6 of 15
Quote:

Originally posted by PinkFloyd
I haven't got the schematic to hand Guzzler but I can safely say it's role isn't to self destruct in unison with the fuses
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Yes....... R3 is on the Andante and I'll tell you exactly what it does or doesn't do this time tomorrow. I'm pretty much taken aback atm and just can't believe my baby blew......... let alone the "fact" I sent her to Wales!!!


Ouch! Sorry to hear that.
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I sure hope the rest of the components are all right.

IIRC R3 is between Andantes ground and the 0V output. So maybe you shorted the + or -15V to 0V in the Chiarra? Don't know if that makes sense.
As you said I only managed to give my R3 a healthy brown finish. But you had to go all the way, eh?
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Good luck with the repairs. Keep us posted.
 
Mar 3, 2004 at 1:03 AM Post #7 of 15
Sorry to hear of your misfortune mike
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It is a good few years since my electrical engineering days but as I recall fuses blow at 7x their nominal rating after hmmm a few minutes (I forget). Either way fuses are generaly intended to prevent fires and not protect equipment.

Assuming you have only altered the amp and not the supply then the fault must lie in the amp which is after the regs. If you have shorted the supplies then the current should be limited to 1 Amp by the regs. But if R3 is a 0.6W resistor and shorting the supply could cause in excess of 2w to be dissipated in R3 then it's lifespan will be greatly reduced.
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I am suggesting that the amp is ok. Is it possible that a single strand of wire is shorting the supply where the cables are soldered to the board? I have known cases where stray wires have been missed when pushing the cable through the pcb holes. You have obviously had to lift the amps pcb up which may have disturbed any stray strands causing a short when the board was put back.

I will be surprised if the amp is damaged.
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Remember R3 sacrificed itself to protect the amp.
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Mar 3, 2004 at 1:21 AM Post #8 of 15
Quote:

Originally posted by maxdamage
Sorry to hear of your misfortune mike
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It is a good few years since my electrical engineering days but as I recall fuses blow at 7x their nominal rating after hmmm a few minutes (I forget). Either way fuses are generaly intended to prevent fires and not protect equipment.

Assuming you have only altered the amp and not the supply then the fault must lie in the amp which is after the regs. If you have shorted the supplies then the current should be limited to 1 Amp by the regs. But if R3 is a 0.6W resistor and shorting the supply could cause in excess of 2w to be dissipated in R3 then it's lifespan will be greatly reduced.
eek.gif


I am suggesting that the amp is ok. Is it possible that a single strand of wire is shorting the supply where the cables are soldered to the board? I have known cases where stray wires have been missed when pushing the cable through the pcb holes. You have obviously had to lift the amps pcb up which may have disturbed any stray strands causing a short when the board was put back.

I will be surprised if the amp is damaged.
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Remember R3 sacrificed itself to protect the amp.
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Thanks............... that makes sense
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I've done my best maxdamage
 
Mar 5, 2004 at 1:01 PM Post #9 of 15
[size=medium]She Lives!!![/size]

Damage report is: The resistor at R3 was replaced and she lives!!!!

Turns out I had short circuited between +/- 15V (loose strand of wire) causing the PSU fuses to blow and R3 to burn out.

Wooooohoooooooooo!!!!! Chiarra is alive
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Mar 5, 2004 at 1:43 PM Post #10 of 15
Quote:

Originally posted by PinkFloyd
[size=medium]She Lives!!![/size]

Damage report is: The resistor at R3 was replaced and she lives!!!!

Turns out I had short circuited between +/- 15V (loose strand of wire) causing the PSU fuses to blow and R3 to burn out.

Wooooohoooooooooo!!!!! Chiarra is alive
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Excellent news Mike, congrats!
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Mar 7, 2004 at 4:06 PM Post #13 of 15
Hi Mike & all members of team Chiara:

I haven't been on line for the past week; into 8th. day of a nasty head cold thewife & I have been trying to get rid of.
I did scan the posts & cocluded the amp should have survived, as did Max Damage. So glad to hear it is ok.
I am making progress with the JLH discrete ckt. Received xfmrs. for a higher voltage P.S., also high current output devices.
I will be offline for 2 wks. The Mrs. & I are going on holiday. Chiara is going with me as we are getting together w Wayne Mc Manus on Grand Cayman next Sunday for a listening session.
Regards: Bill W.
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Mar 7, 2004 at 7:24 PM Post #14 of 15
Quote:

Originally posted by Sewer Guy
Hi Mike & all members of team Chiara:

I haven't been on line for the past week; into 8th. day of a nasty head cold thewife & I have been trying to get rid of.
I did scan the posts & cocluded the amp should have survived, as did Max Damage. So glad to hear it is ok.
I am making progress with the JLH discrete ckt. Received xfmrs. for a higher voltage P.S., also high current output devices.
I will be offline for 2 wks. The Mrs. & I are going on holiday. Chiara is going with me as we are getting together w Wayne Mc Manus on Grand Cayman next Sunday for a listening session.
Regards: Bill W.
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Hi Bill,

Hope your cold gets better, I'm sure the weather on Grand Cayman will help get rid of it :)

The amp suffered no damage but the PSU lost a resistor and blew 2 fuses but all is up an running again.

Lucky amp being taken on holiday, couldn't you squeeze me into your suitcase as well?
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Anyways, have a nice holiday Bill.

All the best.

Mike.

PS: Is that professor McManus by any chance?
 

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