![]() ![]() I have 16VAC coming from the transformer, after BD901 I'm measuring + and - 14VDC, thats really strange shouldn't the votage after rectification go up by an 1.414 ratio? I changed the Bridge Rectifier for a new one and the same happens. I measure it with the + and - legs in the air so it was not connected to the rest of the circuit. Theres one strange thing with the DB901 bridgr rectifier. The only thing that I didnt had time to do today was measuring the resistors one by one because I have to lift one leg up, visually they look fine. Tested all the PSU diodes, all tested wellĪfter the BD901 regulator I'm measuring +-15v instead of +-18.Ĭollector of Q902 I'm measuring +1.7v instead of +12v.Ĭollector of Q903 I'm measuring -0.9v instead of -12v.Īll the other circuit boards are disconnected from the PSU board. Unsoldered Q901, Q902,Q903 and Q904 and verify them with my Atas DCA Pro, all the transistores measured good. ![]() Replaced IC's U901 and U902, these are MC4558 Opamps Replaced BD901 and BD902 Bridge rectifiers Replaced all the PSU Electrolytic caps with new Panasonic 105º I Measured all the voltages at the transformer secondary and every value is spot on. Rainbow colored ribbon cable is handy for this. Write down color=voltage both AC and DC, take it back apart, and see what makes sense, and more importantly, what doesn't make sense. The terminal strip is to keep any wires from touching, causing more problems. I feel your pain.Īnother trick is to tack on a bunch of different color wires to the solder side, and bring them out to a terminal strip to measure while assembled and on. I don't suppose the bottom comes off of this scope? That would make things much easier, very hard to troubleshoot without powering it up. They do need a lot of different voltages, though, all those transistors on heatsinks that hide under the crt. And that little bridge rect, just to the lower left of the big black cap.Ī large portion of the energy used in a scope is the HV to light the crt (the switcher and potted flyback at the bottom of the board with the anode/focus wires?), the rest doesn't need much current, that seems about the right size. I suggest that you replace it, and test all the other caps including the small ones and the semiconductors in that area, starting with the ones on the heatsinks. Take another look at those three caps, the upper blue one appears to be bulging around the Napoleon scribes in the pic. ![]()
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