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Hi ?David , I think you simply click on the attachments button and show the browser where the picture is stored. ?Regarding the + 50 V supply, The supply should be able to start with the ?current gain stages of Q874,Q869, and Q872. The voltage error amplifier should be cut - off as the base of Q860 is much more negative than the base of Q869, which comprises the differential voltage error amplifier . When the power supply is ?+ 50 V, The base of Q860 should be near 0 volts , as the other end of the
differential amp pair , the base of Q869.. At the moment , the current in the diff pair should be all in the Q869 side . The voltage available from the +130 V supply , even though it is substantially less than 130 V, should be enough to cause the output voltage (+50 ) to rise . The + 130 V supply is "lifted" by the + 50 V supply,and th e+ 130 V supply should provide more current to the base of Q872 ?as the supplies increase in voltage? ?I am leaning on one of the transistors in the ?current gain ?stages has no current gain. I suspect the driver transistor , Q869. Perhaps you could unplug it and replace it with a 2N3440 ? it needs to be a transistor capable of a +60 V ?VCE and 1 watt of dissipation . ?The
other likely cause is Q874 , which you can replaced with a 2n 3773 or other high power high voltage T0-3 ?NPN transistor . It looks like some folks are suggesting that it could be replaced with a 2n3055, but the VCE on that transistor is too low in my opinion. ?I have repaired my own 7633 with?similar?problems ?in the past , although it was a long time ago . Mike? From: "bwex@..." To: TekScopes@... Sent: Wednesday, January 25, 2012 12:32 PM Subject: [TekScopes] Re: 7603 no trace
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Hello Jimmy and Magnus. Before I try anything ambitious, I thought that I would attach a picture of 50v part of the low power board with my votage readings written on. Unfortunately, I cannot figure out how to upload a pdf picture of my circuit? Is it possible? Can you exp[lain how to do it? David. --- In TekScopes@..., "magnustoelle" wrote: > > Quote: Back to the +50V supply: It's a little risky, but I'd suggest to > remove Q876, monitor the +50V output with your DVM, and power-up the > scope. ... > > I agree. > > For the next step, I would simply pull connectors P900/P901, then bridge > the sense feedback with the respective supply, and measure the supply > rails again. This requires only five connections and P900/P901 are in > close proximity, so the connections are easy. This is a linear power > supply, not a switched mode supply, so operation with no load does not > harm anything. > > I would also pull P971/P962. > > Doing so disconnects the power supply from its loads and allows > isolation of the trouble to a specific circuit / board by re-connecting > one board after one. > > Just keep going, David - one step at a time. We will bring this beauty > back to life. > > Cheers, > > Magnus > |
