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To keep too much noise off the list, Ozan was gracious enough to work with me off-list to find the problem with my 7B50. It turned out that R594 (the collector supply resistor for Q592) had gone very high (spec'd at 6.81k 1% and was over 18k). I put a 10k resistor in parallel with R594 and the trace started working. I'll get R594 properly replaced but, for now, it's quite wonderful to finally see a trace with that timebase.
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I must say that I was quite surprised to find that resistor had changed value so drastically. I can't tell from looking at it and the parts list doesn't specify, but it resembles either a carbon film or metal film and I wouldn't have suspected there'd be a problem there but anything's possible. Ozan has been so helpful to me - very patiently asking questions about the state of various voltages in various circuits, suggesting more places to look for problems, and finally, zeroing in on the Sweep Start Amplifier as at least one of the possible trouble point, and I want to thank him publicly for his help. Thanks to everyone else who offered suggestions for this as well. I'm not the best at analyzing some of these types of circuits and it is a great help to know there are others here who are willing to provide help. Thanks, Barry - N4BUQ ----- Original Message -----
From: "n4buq" <n4buq@...> Hi Ozan, |
