The AM Forum

2 days ago a friend of mine over in the next county told me he had a rig for sale that he used on AM phone. Asked me if I was interested and did I have anything to trade.  Did tell me the rig no longer worked and the problem was in the display.  He is a collector of radio as myself so I ended up trading even a Johnson messenger two with the tone alert option.

I got the rig home and dove into it head first. First thing I noticed was IC1 header was loose. So removed the display board to find every pin had cracked solder joints. To the extreme I actully removed the header with out desoldering.  Also the 2 pin header by Q3 was the same. So thinking this is going to be an easy fix! I noticed that when reflowing the joints my rosin core solder did not like the old solder on the board.  Ended up getting the desoldering iron and removing all the solder then reflowing again. Kenwood must of used a very high tin content when they built this thing.

My friend told me the display had became intermitted. You could tap the radio and it would come back to life.  It finally died on him.

So looks like my new soldering iron on the tear down bench is going to get a good break in. I can not find any voltage on the display board. So looks like I need to move on to the control board. I disconnected the display board and checked the plugs for voltage to make sure there was not anything on the display board shutting it down.

I love a good challenge

The large three pin voltage regulators in the 430 are also notorious for crystallized or bad solder joints.  Re-flowing the solder on these cures a multitude of problems.

Funny you mentioned that lol. After looking at the schematic I found the 8 volt and 5 volt regulators. Checked and had 8 volts but no 5 volts.  Removed the board and saw that IC9 had cracked solder around all three pins. Go figure lol.

Also found a cracked signal diode just above IC9 on the bottom of the board. Going to hunt that down on the schematic now.  Thinking while I am in there may as well replace C118 and C116. As old as the rig is not a bad idea to replace old caps in the circuit you working on.

Success!
The display now works. So all is not lost.
I do haver other items to address now.
Recieve is down across all bands. Going to have to check all relays and connections on filter board.
No transmit on all bands but I do have a signal out that I can monitor in my IFR1200S. Possible bad vias on the amplifier board.

my 430 had intermittent low receive .... the problem was the band pass filter relay select contacts .... was looking at having to replace the relays when I decided to flow about 5 mA of current thru them with a resistor and series choke ....worked like a charm

That seems to work pretty good. Used a 20k 5 watt resistor into the antenna jack while scrolling through the bands.
Good advise!

Display working like champ now. Still not transmit after checking the amplifier board.
Got to see what is coming from the exciter now.

Since receive is down was hoping to find an issue from relay out causing both problems. Not the case though. Even injecting a signal directly into the receiver it is still down.
Pretty sure there are more bad cracked and cold joints.

FWIW I thought I update this project. The 430 is working like a charm.
The receive and transmit issue was due to the a broken diode under the IF board. D81. This is under the main filter and without it there is no signal. It switches the IF signal path through the crystal filters.
Soldered a ton of cracked joints also.

Congrats on the 430. It really is a nice little radio. I had one for awhile. Mine exhibited synthesizer dropout as it warmed up. I understand that was a common issue.

Thanks!
I am very proud of this one.
I remember reading somewhere that the wax they used in the PLL circuit causes a lot of issues and becomes conductive.  It is there for stability. But when it becomes conductive  it pretty much makes the circuit unstable.  Ithe idea is the scrape it all off. Do not use heat to melt it out though. This will cause this stuff to get in places where you can not get it out like under components.  After all is removes and washed out then replace with bees wax.


I already have a home for this radio. All my ham gear and service equipment is out here in the shop.
I plan on setting up a lab in the house and taking this one there.  Wife is gonna love that!

My TS-440 had similar problems with the display.  Sent it to a friend and he cleaned out all the glop.  Works great now.  I know display problems were common for that particular radio because I've seen ads for kits of replacement parts.

Apparently no lessons were learned at Kenwood by the time they made the TS-820. Mine had the same display issues. Even worse, every time I opened the case to fix one connector or PC board, another one developed problems regardless of how delicately they were treated. On one of those the solution was to go over every trace with a soldering iron to bridge cracks in traces that had developed after production. There were also problems with input filter cores  becoming magnetized and changing inductance. I have to say though, my TS-570D worked perfectly for the ten years I had it.

Bob - NE