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7B92A: Difference between revisions
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[https://vintagetek.org/years-at-tektronix-hofer/ According to Bruce Hofer], early 7B92 models exhibited sweep anomalies especially near the start of the sweep, and after trying to fix these he convinced management that a redesign was needed. This resulted in [[Patent US 4009399A]], the [[7B92A]] update, and the [[067-0657-00]] calibration fixture. | [https://vintagetek.org/years-at-tektronix-hofer/ According to Bruce Hofer], early 7B92 models exhibited sweep anomalies especially near the start of the sweep, and after trying to fix these he convinced management that a redesign was needed. This resulted in [[Patent US 4009399A]], the [[7B92A]] update, and the [[067-0657-00]] calibration fixture. | ||
The 7B92A uses one other custom IC, the [[155-0049-00|155-0049-xx]] sweep control circuit. The internal jumper for mainframe selection (7800/7900/7100 vs. slower) | The 7B92A uses one other custom IC, the [[155-0049-00|155-0049-xx]] sweep control circuit. | ||
in parallel with the | The internal jumper (P834/P835) for mainframe selection (7800/7900/7100 vs. slower) | ||
The effect of this jumper is only noticeable for sweep speeds of 20 μs/Div and faster, since | increases the minimum holdoff time on the slower mainframe selection | ||
by adding a 214 pF capacitor, C835, to pin 8 of the sweep control IC (U820) | |||
in parallel with the other capacitors that are selected by the sweep rate switch. | |||
This increases the minimum pulse width of the holdoff signal on [[7000_Series_plug-in_interface|pin B4]] | |||
so that the sweep logic of slower mainframes can handle it properly. | |||
The effect of this jumper is only noticeable for sweep speeds of 20 μs/Div and faster, | |||
since at those sweep speeds the smallest shunt capacitance is used on pin 8, and the holdoff time is minimal. | |||
==Links== | ==Links== | ||