L2 Audio, PA1000 slave amp

No schematic seemingly available, anyone know if circuit similar to anything else? Owner no longer remembers what the problem was. Protect LED goes from red to green and blue power LED comes on. Cold testing the top layer of bipolar output devices seems ok. Says "professional" on the front but 1/3W resistors thrown in "6 transistor" radio fashion. One base resistor lead is broken, presumably from vibrational resonance fracture of the thin 1/3W wire, but that would not be the problem

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N_Cook
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2009 date but no PbF statement anywhere seen. Strange protect cct, +140V on the red supply and +65V on the black, continuity to +ve of the main bridge rect, but not for the -ve tab. Time to take the amp apart to get to the othe rside of the ps board, no obvious failings there topside. For the moment the smokey staining above one of the 4 TOP66 I'll take to mean it was taking more than its fair share of the remaining 3 after the base resistor failed on one of the 4.
Reply to
N_Cook

A fused piece of 1.5mm pcb trace, warmed up laquer and then a clean break, no smoke staining. I make that about 4 amps carrying capacity for

5 deg C rise along 25mm assuming 2oz board. Anyway this is the main trace between earth bond point and common of the secondaries and the speaker lines, all of which is 20 amp wiring. Another 20A line from this bond point to the input pcb and no heavy wires out from that pcb. So 1/4 inch spade connections to the wiring off the ps board, but on the board just this thin trace to the earth bond wire. Just about goes with the "6 transistor" radio component placement and 2 fudged, topside only, rework replacement components, ie using the cut stubs of the original leads to solder replacements to
Reply to
N_Cook

Uses 2x uPC1237 sil protect ICs one at mains level for full mains rather than bleed for startup and the other for amp problem. Perhaps Green protect LED means pa failure, red for mains switch over failure and orange for both. from user manual "PROTECT indicates at the point of switching the amplifier on for a few seconds. Once they have turned off the amplifier is ready for normal operation. If at any stage, they stay illuminated, a fault has occurred. See section under PROTECT LEDs for more information ... If a fault has occurred on one or both channels the relevant PROTECT LED(s) will stay illuminated and there will be no output "

The output audio relay had one pair of contacts welded closed so perhaps earth failure, due to some sustained imbalance of power out, was picked up by pa protect , and relay cut out on high current passage

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N_Cook

Replaced earth trace with an earth wire, tiny DPDT 8A relay replaced with 2 SPST 15A relays stacked on top of each other. So far so good , stable -80.0,80V rails , mV output, red ->green-> no protect LED sequence at power up . Cannot sensibly check audio until that rat's nest is complete. Just as well took pics, as had not realised black wires were for Dc gnd, plum for -ve and red for +ve

Reply to
N_Cook

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