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564smeter [2015/12/14 09:59] n1eu created |
564smeter [2015/12/14 10:02] n1eu |
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ALC and I recall reports of Tentecs sometimes losing diodes in that | ALC and I recall reports of Tentecs sometimes losing diodes in that | ||
circuit from nearby lightning while connected to an antenna. | circuit from nearby lightning while connected to an antenna. | ||
+ | ----- | ||
+ | //(Omni V s-meter comments that may be applicable)// | ||
+ | |||
+ | As far as I know the manual with circuit diagrams that you can download | ||
+ | from Tentec is all the "service" manual there is. Looking at it I have | ||
+ | found that there is an S-meter sensitivity adjustment R45 on the IF/AF | ||
+ | board along with an S-meter offset R43. It looks like R43 sets the zero | ||
+ | and R45 sets sensitivity from low to very high. I don't know the value, | ||
+ | but there is no fixed resistor to limit hypersensitivity. Providing the | ||
+ | AGC is enabled, you should be able to adjust R45 to any sensitivity you | ||
+ | like, providing the pot hasn't gone bad with age. If the pot has an open | ||
+ | resistive element it may only work set up way too high. The pot may have | ||
+ | an identification resistance on it to allow finding a generic | ||
+ | replacement or to allow a will guess for value, at about 1/2 the pot's | ||
+ | total resistance to be put in as a fixed resistor. | ||
+ | |||
+ | The other thing that can cause an S-meter to be hypersensitive is leaky | ||
+ | bypasses on the AGC line so that AGC control is poor, e.g. that it takes | ||
+ | a large AGC voltage to reduce the RF and IF gain. Maybe the RF gain | ||
+ | controlled stage is on another board and the cable between them is open. | ||
+ | It might be two common Tentec service procedures are in order. One is to | ||
+ | tighten all the board mounting screws to make sure the grounds are good. | ||
+ | The other is to apply a quarter drop of DeoxIT to each cable connector | ||
+ | pin and slide the connector off and on a few times to get a solid | ||
+ | connection again. | ||
+ | |||
+ | If all that's needed is setting R45, you will have to judge by ear what | ||
+ | signals are strong and weak, like we did before we could run AGC on a | ||
+ | receiver on CW or SSB, and adjust the meter for a satisfying reading | ||
+ | that matches your perception by ear. | ||
+ | |||
+ | If R45 proves to be open, Cramolin who makes DeoxIT makes a pot restorer | ||
+ | product that might work. |