Richard,
Following up on Bob's comments, check if the scope has been modified to silicon diodes, or does it still have the original selenium plate rectifiers? There was a mod kit to convert the scope to silicon diodes. The forward resistance of the original selenium rectifiers increases substantially as they age, so after 5 decades the forward drop will probably be lower than the regulated voltages. The resistance also increases with temperature.
Essentially, selenium rectifiers must be replaced when they are this old. But you can't just put in silicon diodes with high enough PIV ratings. Even new, the selenium rectifiers had considerable forward resistance, which was factored into the design. Silicon diodes require the addition of an additional resistor to prevent overstressing the regulator tubes. I don't know what the correct value is for the 310 scope ¨C perhaps a member who has access to the mod kit instructions will know this.
The other thing to watch out for with the original (non-`A' model) 310 is intermittent contact with the rivets which connected the two layers of the circuit boards together. Through hole plating of two sided circuit boards had not been invented when the 310 was designed. Tek used rivets pressed into holes in the board to connect the layers together. Components were soldered to the inside of the rivet, but the rivet itself relied on the tension in the flanges from when it was installed as the only contact to the circuit board traces. This proved to be extremely unreliable, forcing Tek to introduce the 310A, which was the same circuitry, but implemented on trusted ceramic strip construction.
With a lot of tenacity, it is possible to gently clean the pad area of the trace surrounding the rivet and the rivet flange itself with a small piece of steel wool. Once the oxide is removed, you can go through with a soldering iron of the proper size and tack a bit of solder to bridge the rivet flange to the trace. You only need to make the bridge in one spot, not over the entire flange area. Heat only the rivet with the soldering iron, as the foil bond to the substrate in this generation of circuit board is very intolerant of excessive heat.
- Steve
--- In
TekScopes@..., Bob Albert wrote:
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> Measure the power supply voltages.?? If they droop after a while, suspect the rectifiers.
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> Bob
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> --- On Tue, 10/9/12, DiPaolo Richard wrote:
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> From: DiPaolo Richard
> Subject: [TekScopes] Tekronix 310 question
> To: "
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> Date: Tuesday, October 9, 2012, 3:31 PM
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> ?????????? I have a Tektronix 310 that the scope fades after about 15 minutes of being turned on. Any experience in this area would be appreciated. My guess is CRT? Not sure. Anyone?
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