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There seems to have been a flaw in the design of the power supplies that cause then to fail way too early, after a few years of being on for many hours.
A similar story is found at the blog from Drew Brashler: https://brashleraudio.wordpress.com/2012/08/12/power-supply-woes/
Some mixers have had multiple repairs/swapped power supplies. The supply may be found in Soundcraft Spirit M4, M8 & M12. Product presentation at https://www.soundcraft.com/en/products/soundcraft-m-series . Still on sale in 2015.
Photos from a faulty M4 power supply in this album, and below. The main switching transistor was shorted out, and electrolytic capacitors looked to be fine visually and not shorted.
PCB code: SC4105-06
Notes in Danish:
FET1 kortsluttet fra drain til source, 25 ohm fra channel til gate.
keramisk SMD-kondensator C28 parallelt med IC’ens forsynings-spænding er kortsluttet.
Modstanden R17 mellem IC og gate på switch-transistoren er kraftigt forkullet/brændt af (afbrudt).
‘Current Sense’: tre parallel brun sort guld guld (1 ohm?).
R45 gul lilla sort sort brun (470 ohm, 1%?, i brændt tilstand måler den godt 13k ohm)
329 ohm over parallelkoblede R36, R47 (på foto af Brashlers M12, ligner de 680 ohm, ligesom de to tilsvarende modstande på Soundcraft E6 her: http://www.neufeld.newton.ks.us/electronics/?p=498 , og de svedne måler 673 ohm)
C37 og C38 er 47uF 50 V. Det er vist normalt
Ingen lytter var kortsluttet
TIP31A transistor (serieregulator) ved siden af 25 V lytter.
IC SMPS controller: UC2857AN (kortsluttet?)
Vcc: ben 7
GND: ben 5
Gate driver out: ben 6
Isense: ben 3
Vref (til elektroly): ben 8
comp: ben 1
Osc: ben 8
feedback: ben 8
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