Hartke A70 Combo, 2006

High f squeel the owner could cut out by dropping the 5K graphic to bottom. With graphic as normal he also found that touching 1/4 inch jack ring to chassis would stop it. Of couse no appearance in my hands. Mains ground is properly bonded to chassis, I've not yet found where amp 0 is connected to chassis though it is (at the moment) , insulated bush 1/4 inch jacks throughout. Known issue with these ? I'm assuming the crosslink point, wherever it lies, is lifting intermittently. I note the coachbolt through the toroid is not making electrical contact to the chassis , thru the paint , so maybe similar wherever the amp ground is , DI XLR con perhaps. Not yet , testing per section, taken apart yet.

Ground crosslinking under the 2 input sockets via inadequate "star washer" metal and paint not scraped off the casing , bush nuts not loose just not fully tight , more than finger tight, enough slack to make intermittant I suppose . Early China PbF so lots of nasty heatsinky solder points, laying in wait, to rework, especially as pcb holes are far bigger than the leads in most cases. Once again rigid chassis fixed heatsink and o/p devices fixed to free-to-resonate pcb so a fillet of hot melt above and below at the join to dampen and cross-fix by more than just PbF solder points. No mention of PbF on boards or green warning stickers. One saving grace none of that waste of time and space white-goo between heatsink and casing to remove, before working on the board.