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Author Topic: Tempo One ( Yaesu FT-200 ) restoration and thoughts  (Read 819 times)

N2EY

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Re: Tempo One ( Yaesu FT-200 ) restoration and thoughts
« Reply #15 on: October 26, 2022, 01:50:02 PM »


As a restorer I would not usually do that since restoration involves maintaining the rig as close to factory as possible. For those not interested in restoration as much as repair or even improving upon the unit, then it may be a good idea from a reliability point of view but not necessarily for improved performance.

For example, a 7809 regulator could conceivably replace nearly all the discrete parts in the +9 V regulator but the drift specification of the 7809 is -1 mV/degree C ( see link below for specifications )

https://pdf1.alldatasheet.com/datasheet-pdf/view/888521/SEMTECH_ELEC/7809.html

The measured temperature change at the +9V regulator/RC oscillator board is about 23 degree C, so the typical drift with the 7809 might be around -23 mV vs 40 mV for the unmodified regulator with carbon composition resistors. As described earlier the 40 mV drift  can be improved considerably just by using metal film resistors.

The 7809 should be more reliable since it eliminates a large number of parts and soldered connections including the adjustment potentiometer, VR501.

Before I changed the four carbon composition resistors, I was sent this link which contains a modification to use a common three terminal regulator, the 7805.

http://vk2yld.info/ft200.htm

I have no idea how many hams might have followed this change, but I am not sure the problem was ever really solved since the drift after the solution is still 130 mV which is more than three times worse than the unmodified but properly functioning regulator.

Good points all - thanks!

73 de Jim, N2EY
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HAMHOCK75

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Re: Tempo One ( Yaesu FT-200 ) restoration and thoughts
« Reply #16 on: November 01, 2022, 08:19:42 PM »

Alignment of the “grid” or preselector circuits was completed. Yaesu’s procedure calls for alignment starting in receive mode, then doing it a second time in transmitter alignment before doing neutralization last.

Following Yaesu’s procedure showed no instability in receive mode, but when adjusting L9, 14 in transmit mode on 15M, instability occurred. The instability went away if neutralization is done on 15M before adjusting L9, 14. I found the procedure shown in the table below worked better. The plate current was kept under about 100 mA during the tune up.

The purpose of the L2 9 MHz trap is fairly obvious since the instructions call for supplying a 9 MHz signal at the input, then tuning for a null on the S meter. There is no explanation for how to adjust the L1 trap in the manual which is at the input to a cathode follower which drives the receiver mixer. I left the signal generator at 9 MHz at the input and adjusted both L1 and L2 for a null in the S meter reading as both L1 and L2 are identified as 9 MHz traps in the material list.

The manual calls for the adjustment of a trap coil L22 but L22 does not appear either in the schematic or material list.

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