EB5AGV's Workbench: Kenwood TS-850S repair
Some common troubles of this popular transceiver
Here you have some pictures and comments of several repairs done to different TS-850S. As it is a rig I repair frequently, I will add more information as soon as I work on them. Hope it helps!
Problem#1: NONWORKING DISPLAY
One of the failures I have found in several units is a faulty display. It can be intermittent or permanent and cause could be the same: there is a capacitor which leaks and destroys a circuit trace and/or vias.
Repair done at the other PCB side to replace damaged trace
IMPORTANT: Please, note that this is a particular case of the failure; other traces or vias could be damaged. Also, be sure that, if you add any wire, it is soldered correctly. Don't trust just the pictures, as there are some very close vias and traces which are not connected.
Problem#2: NONWORKING OR LOW AUDIO
This could be due to a leaking capacitor in the audio power amplifier zone (bottom side of the rig)
What is below the cap...
Problem#3: PLL UNLOCK / FREQUENCY JUMPS
This is another case of bad SMD capacitors, in this case in the CAR UNIT.
This problem manifests itself as complete PLL unlock or sometimes just as some instability. To find out tune a CW carrier and check if it is crystal clear... if not, you can have this problem developing. Anyway, even if you don't find anything wrong, I would check caps, as ALL the units I have checked had this problem.
You can see how bad it could be in the following pictures. Original caps are rated 16V. I replace them by 35V units.
Cleaned board
Fixed board!
Already back on its place
Problem#4: STATIC-LIKE NOISE (even without antenna connected)
Just another classic. A damaged Q49 transistor on the RF UNIT generates this. It is a transistor which adds some attenuation (20dB) on transmission to the receiver so it is not overloaded. But if it fails and gets intermittent, it causes all kind of static-like noises. It is just a 'digital' transistor (with internal biasing resistors), type DTC124EK, and it is very cheap.
In the Service Manual schematics, it is located on page 121 (both PDF and real page numbers are the same), on the top left corner, labelled as RF SW.
Here you have some pictures to help on the physical location:
More to come soon... keep tuned!