Kenwood TS-700S

[arkansasbill]

I am trying to troubleshoot the FM mode receive part of this all mode 2 meter receive. No squelch action and no audio out of the discriminator (noise in the absence of a receive signal or receive audio). I can use a AM receiver set to 455 KHz and detect the incoming signal (on the output of the discriminator transformer) by slope tuning the AM receiver. However, that is as far as I can get. A Oscope shows the present of 455 FM on the discriminator diodes. I have replaced the diodes and the electrolytic cap in the discriminator circuit to no avial. Any ideas anyone.
Thanks,
Bill KC5MN

[WA9WVX]

Hello Bill,

You should generally have your Squelch Control at minimum while measuring the Noise Waveform out of the Discriminator and slowly increase the Squelch Control perhaps half way which should provide plenty of the Noise signal to the Squelch circ uitry. I haven't downloaded the TS700S schematic yet but i will do so in a bit.

Was the transceiver working OK before this problem appeared or have you pulled the unit from storage and discovered the failure? I'm thinking the TS700S is a 30 year old transceiver which can produce "Cold Solder" connections over a period of time. And other failures such as Electrolytic capacitors could have dried out in the Audio / Squelch circuitry. I've also experienced I.F. Crystal Filters going defective. You would need a Good Signal Generator set at 1000uV connected to the 50-Ohm RF Input and Scope any losses through the I.F. circuitry.

73,

Dan
WA9WVX

[WA9WVX]

Hello Bill,

I recommend going to the following website and downloading the TS-700S Service Manual:

http://www.mods.dk/manual.php?brand=kenwood

This Service Manual provides a Troubleshooting Chart, Voltages, Waveforms, Block Diagram, Schematics and Part List & Numbers. Your Receiver Squelch problem may lie in the Crystal I.F. being 10.7 MHz and/or 455 KHz. Potentiometer VR7 is the Squelch Control and it sends the Noise to Q14, Q15, Q16 & Q17 and out on F AF to the Audio Board. There are a string of Electrolytic Capacitors throughout that circuitry that possibly have dried out or shorted (such as C49 & C51) preventing the proper amount of Noise amplication signal to be generated for the Squelch to function properly. I would highly recommend using a Scope while tracing the signal through this circuit. It would be a wise idea to verify that the various DC Voltages are present on the PC Board, there could be a Power Supply failure too.

I'll be checking your progress every few days here so if you have any questions, feel free to ask and I will reply.

73,

Dan
WA9WVX