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7704A Repair and modules.
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Bob H.
Good Evening
I have a 7704A mainframe that is in need of repair. I turned it on this morning after not having been powered up for about 2 years. The trace was moving around erratically. Then I heard a sizzling sound (never a good sound) and immediately turned it off but not before a whisp of smoke emerged from the bottom of the scope. I live in the Atlanta metro area and would like to find a company or individual who is able to repair it. Also I am in need of a horizontal sweep module. I'm not sure what model I am looking for. This scope will be primarily used for audio frequency applications. Any hints or suggestions would be very helpful. The modules I have are 2 7A26 and 1 7A16P that is also in need of repair. Any help would be greatly appreciated. Thanks Bob |
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--- In TekScopes@y..., "Bob H." <fisher_c_body@y...> wrote:
Good EveningThe trace was moving around erratically. Then I heard a sizzling soundOften the Tantals for Supply Decoupling having a short. The Chokes which are located before them then usualy smoke. (at least in the last week i have repaired a 7A26 with such a failure) For mostly audio frequencies a 7B53(A) would be the right choice for the time base plug in. Jorgen dj0ud |
I have a 7704A mainframe that is in need of repair... For mostly audio frequencies a 7B53(A) would be the right choice forThe 7B53/7B53A is not recommended for use in the 7704/7704A. I don't remember why, but I think it was a good reason. The original poster needs to find a 7B70+7B71, 7B80+7B85, or 7B92/7B92A. |
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There's not a darned thing wrong with using a 7B53A in a 7704 or
7704A. It's the 7B92/A that you can't easily use on lower bandwidth scopes only because they can't handle the faster sweeps. And 7B53A's are so plentiful that they should be cheap. Having to come up with and pay for a pair of 7B7x or 7B8x is a lot more difficult and expensive -- and you'll need two service manuals instead of one. And the 7B53A leaves a horizontal compartment free for a counter or DMM. |
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Stan or Patricia Griffiths
As I recall, the reason Tek would not recommend a 7B53 as a timebase for a
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7704 is that it will not sweep fast enough to take full advantage of the 7704's 200 MHz bandpass. Other than that, I believe it will work just fine. An even simpler, and probably cheaper, timebase would be a 7B50 or 7B50A with does not have the delayed sweep feature. You could even use a 7B51 that is normally used with a 7B50 to provide delayed sweep but can be used as a simple timebase without a 7B50. I only suggest the 7B50, 7B50A, and 7B51 because they might be more available and cheaper than the 7B53/A alternatives. There was also an earlier version of the 7B53 called the 7B52 which would work as well . . . I really need to get on with finishing my second book . . . Stan w7ni@... dd@... wrote: I have a 7704A mainframe that is in need of repair... |
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Stan or Patricia Griffiths
Hi Bob,
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There is some possible incompatibility using the 7A16P in a normal 7K mainframe such as the 7704A. The 7A16P was specifically made to be used with the 7912AD digitizer and is programmable (that's what the "P" on 7A16P means). Anyway, I have read a note that says the additional circuitry for implementing programmability in the 7A16P may overload one or more of the 7704A's power supplies causing some unpredictable results in all the other circuits powered by them. You might try it with caution. You might get lucky and not cause any permanent damage and it might even work for you. There is probably a way to disable some of that extra circuitry in the 7A16P without damaging it as a nonprogrammable amplifier and reducing the power supply load to an acceptable level. I have not looked into that yet. Future project . . . Stan w7ni@... Bob H. wrote: Good Evening |
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