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Hi,
I have just built the Placid HD BP, it tested fine (off load) and I adjusted it to 14V output and 250mA current as per the instructions. I have had it powered at least 6 times, testing it. I just connected it to a Legato, and the rectifiers let out the magic smoke...
I notice that there is a similar failure from another user. I wanted the Placid HD BP v2 anyway and just ordered it, but I'm wondering why this fault might have occurred? If there are any clues, I would be very interested. The transformer is 2 x 13v. Next time I'll test it on load.
I have a single Placid HD to complete soon and I don't want the same thing to happen with it.
Thanks for any tips,
Paul
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The transformer - is that a 13-0-13 (centre tapped) or 13-0 // 13-0 (2 separate windings) ?
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Is the transformer dual secondary (4 output wires) or center-tapped (3 output wires)? EDIT: Looks like AVR beat me to it... Edited by user Monday, June 9, 2014 7:09:39 PM(UTC)
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It is 2 separate windings, isolated, and connected to the two separate AC connections for the Placid. I kept the phase the same on both halves, probably because I'm anal retentive... The supply was working fine before I connected it to the Legato. Also, there are no shorts on the Legato PSU connection, I've checked. It looks like an over current failure to me, but I'm wondering what triggered it to go so over current. Edited by user Monday, June 9, 2014 10:19:16 PM(UTC)
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Originally Posted by: t-dog  and connected to the two separate AC connections for the Placid. I kept the phase the same on both halves, probably because I'm anal retentive... I would definitely not do that. I can't think of any benefit. Quote:
The supply was working fine before I connected it to the Legato. Also, there are no shorts on the Legato PSU connection, I've checked.
It looks like an over current failure to me, but I'm wondering what triggered it to go so over current.
Try measuring the resistance between + GND and - on the Legato with nothing connected to it.
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The power input to the Legato is high impedance, not shorted or very low impedance. I did not measure exactly how high it was. I will rebuild the PSU tonight and report back.
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So I rebuilt the Placid HD with a new bridge rectifier, reset the trimmers and powered it up. When connected to the Legato it appears to work ok (I tested it first with a dummy load): - I can adjust the output to +/- 14V without problems - I can adjust the current up to 300mA without issue, with 300mV across R1 and 90mV across R2 So it _looks_ ok, but when I put a scope on it I get the attached traces, about 6mV of 100Hz ripple. I have checked the reference voltage and it is clean with minimal noise. Is this this much ripple acceptable behaviour for a Placid HD regulator? I would have thought not, but I might be wrong. If it is out of spec, any idea where to start debugging? The CCS and shunt transistor pairs measure ok in circuit (but may have to remove them to check properly). Many thanks, Paul Edited by user Tuesday, June 17, 2014 6:53:25 AM(UTC)
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Is the scope trace taken at output ? Pls. read this threatIn short - it might be default behaviour - and it can be cured.
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Many thanks avr300 - the scope traces are the positive and negative outputs at the Legato, i.e. after about 5 inches of twisted power cabling.
I will read the other thread now. I hope it leads to a solution!
Thanks again.
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Thanks again avr300 - the link you sent me to and Russ' mods there have fixed my problem - even though my VREF was clean, the ripple must have been getting into the error amp via the emitters.
Thanks again,
p
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