Anyone fmiliar with these ? One ch down but nothing visibly or rhinally amiss inside. Not powered up at all , just cold exploring at the moment. Is there output relays lurking under the main board? Triac crowbar ccts on the o/ps ?
Would any Mackie amp be similar? Comes apart easier than it looks, not one large board, 2 sparated pcb and heatsinks. Still nothing seen amiss so presumably false protection, at least no microcontroller seen. Plenty of SM under the pcbs but analogue seemingly.
Hopefully Mackie M 1400 will be similar enough , NJM13700 and LM311 instead of LM338 for muting and supervision
How do American repairers get on with PbF boards, not marked as PbF. Is there an overlay codification meaning PbF or LF ? Has anyone collated together what USA makers + models for what 21C years definitely had PbF or definitely had leaded solder? Or putting it another way , what is the probability of any China manufacturer using leaded solder in 2001/ .../2007/ ... ? This amp made in China in 2007, for USA, exported to UK. Balance of probabilities from appearance, indentation test etc is probably PbF. Yet again faced with repairing a "fully working" but intermittant failure PbF amp However much tugging and twisting on input and output and pot boards cannot get either channel to fail, as user contact there, most likely failure areas. Closely inspecting all boards - no bad-contact solder found. So far powering to 75 percent mains, noting some mid-amp signal AC and DCs , as nothing useful out there on this amp. Before upping the mains (may of course cause a protect failure in one ch from that) . And before seriously attacking the main amps with engraver tool and nylon bolt as tip , monitoring large dummy loads with attenuated phones, to try and make a failure.
Wanging everything with engraving tool + nylon bolt eventually elucidated. Loss of ch 2 , no prob on its i/p board, due to bad mono/stereo/bridge slide sw on the ch1 i/p board. Unusual DC rails for the SMD opamps , will go on my tips files for anyone else confused by this. One operates from -113V and -101V supplies and the other 40V and 55V, same for both ch
A right pain to desolder, double sided thin board, thin traces, tiny pads , plated thru holes and PbF solder. 19 inch rack amp but with unnecessary miniature complex asymmetric switch impossible to find replacement for, 4 pole,3 way, but only 8 of the 16 pins used here. "re-soldered" with copious flux before hot-air desoldering because of extra PbF temp . Not contacts corrossion it would seem. I suspect sloppy phosphor bronze contact carrier/slider in outer metal shell, will rebuild with 0.5mm hard PTFE strip padding out one side to stop it flopping about, and cleaning contacts. Maker YSC logo and also DC stamped on the outer.
there is a potential safety issue with these. On reassembly make sure the mains switch crimp connectors are pointed downwards, easy to have bent them up to nearer normal straight rearwards, in moving wires and boards about. If straight out , then the plastic of the crimp will get squashed into the edge of the pcb with nearest track just 1mm away from mains connection.
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