Kenwood TS-940

[redlght]

After a power supply problem was fixed now When keyed the first 2 relays in the filter board just chatter on all bands and modes no power output on watt meter and chatter can be heard through speaker. The radio before only was doing 50 watts now nothing.

[MDYoungblood]

Could the chattering your are hearing be the automatic antenna tuner. I have seen the drive motors strip the shaft and continues to try to tune for a couple minutes, this will also cause no wattage output, it might even cause the relays to chatter. Had a similar problem with an Icom radio.

3's

Greg

[redlght]

It is the filter board after checking depending on band that's the relay that chatters. In thinking the PA board isn't providing enough rf output.

[MDYoungblood]

Could be this, http://www.eham.net/ehamforum ... 134.0;wap2

3's

Greg

[redlght]

Someone used cb finals for drivers and added a v reg since they are 12volt and the 940 uses 28. One of the drivers was blown I am waiting for parts to set it back OEM. More to come...........

-- Tuesday, 21 February 2017, 16:00 PM --

New driver still chatters ugh

-- Saturday, 25 February 2017, 17:38 PM --

Gave up and sent it on it's way. worst radio i ever worked on, the way it was designed with so many voltages of 42 at the source and 29.1/23/12/8/5 when the supply takes a cr#p it sends 40 volts every where.

[redlght]

I got it back lol changed out the pa board and LPF board same stuff no change, I posed this question in qrz and got slammed for using a screen name lol sign up said either so i picked sn what a warm welcome i got here.lol

[MDYoungblood]

I got it back lol changed out the pa board and LPF board same stuff no change, I posed this question in qrz and got slammed for using a screen name lol sign up said either so i picked sn what a warm welcome i got here.lol

Yep, QRZ and QTH has it's share of "Trolls" watching everyday for a non ham to ask a legitimate question, nothing better to do. Want to really get them going ask about a MARS mod,, lol.

3's

Greg

[redlght]

lol I bet that would get the fight started for sure. This was the reply i got from the gawds over there:

"Why so coy about your location? If you are a licensed ham, you should say so. If not, you're probably not going to get the level of support you think necessary. As you can see, no one else is even taking the time to give you any info. There is a reason for that, and if you are a ham folks will be more giving of their time and so on. In the end, it's your choice. Good luck with the repair, you're going to need it."

[bluemeanie]

I just posted on the thread I'm about to be stoned for it. Gonna stir it up again Yea haa

[redlght]

I wouldn't give them my call if my life depended on it. I could see if it was on air but a net forums that is not an official FCC forums and my call sign is so important to them? LOL nothing more than a group of people that can not stand not knowing some thing about every one they meet.

Only thing my ticket says is I got more than 70% out of 35 questions correct, My main knowledge came from hands on working on stuff for the past 40 years a lot other than cb or hf radios.

[redlght]

Just updating this thread, It was a problem in the AVR board breaking down under load causing the chatter on tx.

Was showing a voltage drop of more than 4 volts on tx now it has less than a .6 volt drop and works on all bands full power.

I really got a good schooling on TS-940's lol, i worked on 3 of them all are now back in service.

[MDYoungblood]

Cool, now I know who to send one to if I run across one.

3's

Greg

[redlght]

No problem any time, I know them very well now. If you rebuild the avr unit you will find that parts are hard to find and some subs are needed.

The values of the replacement diodes are different than the OEM ones and do not load the circuit enough to be able to adjust the 28 volt PA line, It needs at least 150MA of draw for the regulation to start or VR1 will not adjust it to 28.5 volts. So you add a 22k resistor across D3 that will load the circuit and allow VR1 to do it's job with replacement parts.

D6 Is a SV03YS it has a 3 diode junction internally and there is no sub for that and they are like 8 dollars a piece if you can find them. I may try to use 3 separate diodes as a replacement on a spare avr board. It is a good idea to move the 15amp fuse to the feed side of Q101 and 102 because in all 3 radios that the power supply blew up in because of C12 getting over heated by the diode bridge none ever blew that fuse and that allows 40+ volts to wreck the avr and PA boards.

Another note every time you turn off an unmodded TS-940 it goes unregulated for a second or 2 until the big filter caps bleed off and blows 40+ volts in to the radio. You can see this voltage spike looking at the power supply on a scope.

[tgbrail]

My TS940s now has an issue . when you push the power button , the lcd screen that lights up "Trio Kenwood" shows up with a row of faint squares.
After repeated power ons , it comes around and works fine .
Its been fully recapped by a great tech in our area .
Not loosing any sleep over it unless it totally stops showing up .