OBSERVATIONS FROM SCOTLAND 26 May 2008 GM1SXX
Repairing the Yaesu FT102 Transceiver.... continued
With the driver stage now working, I turned my attention to the PA stage and a general tidy-up of the radio.
The FT102 uses a LOT of point-to-point wiring. Much of this is carrying low voltages and low level signals but some of it carries lethal voltages.
In particular, the 900V DC HT supply appears on the rectifier PCB on the underside of the set. There is no advice as to this lethal voltage being present. furthermore, as pointed out to me by FT102 guru Mal Eiselman NC4L. some wires carrying low voltages run in close proximity to the bare pins carrying the 900V supply. Clearly this is a bad idea!
The photo below, shows the PCB as I found it. On the left side, note the thin purple wire wrapped around the thick clear wire.
That clear wire is carrying 900V DC and connected to a bare solder tag!
The radio can be made safer by desoldering the purple wire and re-routing it away from the High Voltage pin. Ty-Wraps allow the wiring bundle to be routed away from these live pins as shown below. I also added a warning label, something I feel Yaesu should have added.. Note the dirt and dust clinging to the High Voltage diodes.
In the photo, you can clearly see the bare tag marked 900 on the left hand side near the ty-wrap. One has to wonder why Yaesu were so careless when they built these radios. 900Volts DC could spoil your whole day... or life.
After tidying things up, I replaced the three PA valves and tried out the radio into a dummy load. Everything seems to work as advertised and the PA idling current is exactly correct. I'm happy to have repaired this beautiful old HF radio and saved it from the scrapyard. Cosmetically, It's very good indeed, just a few very minor paint chips. I'll repair these with Ford car touch-up paint.
73 AL.
GM1SXX
73 AL.
GM1SXX