Kenwood tm-221 help wanted please. - Page 1
Forum section: electronics / projects

author: christopher iles
author_rank: Regular Contributor
timestamp: May 24, 2014, 06:12:41 am
content: Hello,My TM-221 was working fine until one day when I switched it on it doesn't receive. Transmit is fine, full power and clear audio. On receive I just get white noise. I've checked the ctcss is not running and when I transmit on my handheld rig a few feet away I can (just barely) hear the signal.I've done the obvious checks I think (dry joints, loose connectors, cooked components) and all seems ok.My feeling is that it's something simple that I haven't spotted...any ideas please?Grateful for all suggestions, thank you.Chris.

author: DonRon
author_rank: Regular Contributor
timestamp: May 24, 2014, 06:42:32 am
content: Hello Chris,Did you try to use an external speaker?Did you make a master-reset?Cheers,RonaldPS: I don't have the TM-221.

author: christopher iles
author_rank: Regular Contributor
timestamp: May 24, 2014, 07:18:49 am
content: Thanks for the reply, I have noise coming out of the internal speaker but no signals, also I have reset the radio. Still no joy.

author: babysitter
author_rank: Frequent Contributor
timestamp: May 24, 2014, 11:57:00 am
content: Full Audio loudness or is it muted? Internal Beep okay? Af Amp.Normal loud noise? Check Antenna connector, although tx in proximity should always work.

author: christopher iles
author_rank: Regular Contributor
timestamp: May 25, 2014, 04:57:11 am
content: Yes, full audio, not muted. I've checked the aerial connections and all is ok (no open-circuits or shorts) it's as if I'm tuned to an empty channel/frequency even when I know that channel is busy (got my ht tuned to the same frequency). Thought it may be a PLL problem however transmit is fine and spot on frequency.Maybe the rf preamp has stopped working, but strange as the rig was working fine before the last switch on.Regards,Chris.

author: babysitter
author_rank: Frequent Contributor
timestamp: May 25, 2014, 02:06:49 pm
content: Can you inject a zf Signal? Helps to locate relative to injection point.You can tr yto listen to the lo Signal coming fromm the pll during rx with another Radio.

author: babysitter
author_rank: Frequent Contributor
timestamp: May 25, 2014, 06:09:22 pm
content: Sorry for my very reduced answers, I was only online with a Mobilephone the last days. So I will try to compensate a bit:PLL Check: You can listen to the LO frequency, its depending on design either 2 times ZF above or below your RX frequency.If you can hear it the signal is here for certain but you dont know the level. Barely audible reception and OK TX path looks suspicious like PLL is OK.The exclusively used for RX parts should be antenna switch, either relay (ohmmeter, coil voltage) or diodes (bias voltage).The preamp (DC levels around this transistor OK? Putting screwdriver between preamp and mixer as secondary antenna is a bad but sometimes working idea) and the mixer. If you can inject a ZF signal behind the mixer, e.g. taken from another radio, you can check the demodulator.

author: Rory
author_rank: Frequent Contributor
timestamp: May 25, 2014, 06:32:59 pm
content: Service manual here:http://www.qsl.net/4/4x6on/RADIO%20MANUALS/KENWOOD/KENWOOD--TM-221-Sevice-Manual.pdf

author: christopher iles
author_rank: Regular Contributor
timestamp: May 26, 2014, 05:27:10 am
content: Hello and thank you all very much for your most helpful ideas and suggestions. I'm determined to find this fault and will be sure to let you all know what it was when I do.Very grateful to all.Regards,Chris.