Re: TEK465 Horizontal trace
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Or Amazon Prime! LOL.
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I guess I have a bias against Amazon for such things. Kind of like Radio Shack. But why? I guess as long as I shop carefully and understand I might not be getting the best quality product. Why not? I see packages of assorted types for cheap. Might be worth having a variety. Thanks for kicking me in a different direction Bob! Dave On Wednesday, March 3, 2021, 09:07:18 AM PST, Bob Albert via groups.io <bob91343@...> wrote:
I read somewhere that you get free shipping from DigiKey if you prepay with a check. Bob ? ? On Wednesday, March 3, 2021, 08:56:35 AM PST, Dave Peterson via groups.io <davidpinsf@...> wrote: ? I have removed Q1226/Q1236 PNPs with no effect. They are not part of the problem. This is also part of why I built the LTspice simulation - to get insight into the current switching going on. I've also tested changing horizontal position, as well as unplugging them entirely at P1200 with no effect. My finding is that, while yes, the Q1224/Q1234 currents drive the signals through the front end of the amp, it doesn't mean that there aren't corresponding voltage signals. The simulation confirms that an excessive negative bias on the input results in the symptoms observed on the bench. It's not a matter of unobservable currents. I've been chasing the theory that something is pulling the base of Q1224 down, but sleeping on it allowed me to realize that perhaps the issue isn't a pull down, but a weak pull up. As the PNP Q1098 has a problem, perhaps Q1038 does as well. The node at Q1224 base is a huge common point of a lot of drivers. Q1038/Q1098 are significant contributors. I need to order up some fresh 2N3906's, but it occurred to me that the system is likely designed to have Q1038/Q1098 contributing, even if B-sweep is inactive. I'm thinking about borrowing Q1226 and Q1236 for Q1038/Q1098. I'm hesitant to take them from my working 465 lest I damage them and kill a second scope. I need to accumulate some components to order so I can mitigate the shipping charges from Mouser. Even 100 2N3906's are less than the $8.00 shipping. Dave ? ? On Wednesday, March 3, 2021, 02:47:36 AM PST, G?ran Krusell <mc1648pp@...> wrote: Hi Dave, if you remove Q1038 and Q1098, set POSITION pots to center position, sweep through the TIME/DIV positions, no X AXIS signal, what do you have at Q1224 base? Measure and calculate the current through R1223, 806 ohm. Calculate the various currents going to/from Q1224 base. Does anything make sense? G?ran |
Dave Peterson