This was bought as a working unit, but when it arrived I was surprised to find that it didn't actually work.
Correspondence with the previous owner convinced me that it had been working right up until the time when it was packed up for dispatch to me, and that the problem I was facing was related to the journey to me. Although not in the original manufacturer's carton, the unit had been well packed and externally appeared to have arrived in good order.
As a matter of fact, cosmetically, it is in very good condition indeed, there is even an original factory inspector's label attached to the case. So I had to set about figuring out what was wrong, and how to fix it, so out with the manuals, and off with the covers.
| WARNING! | With the covers off, EVEN IN RECEIVE MODE there are potentially dangerous high voltages present in various parts of the radio, in particular within the PA compartment and around the Rectifier A board on the underside. |
| Even if the rig has been disconnected from the mains for some time, it may take several minutes for these voltages to decay to a safe level. | |
| If you are uncomfortable working around equipment where this is an issue, then don't even think about repairing your radio, refer it to a specialist! |
It quickly became apparent that there was no 12V dc coming from the 12V distribution points on the Rectifier A (PB-1967) board. There appeared to be a discontinuity between the rectifier diodes (D05 and D06) cathodes and the remainder of the regulator circuitry.
| Tip #1 | With the rig disconnected from the mains supply, it is possible to power the low power parts of the unit including the entire receiver and a good part of the transmitter from an external low voltage DC power supply. |
| If the power supply is variable, set it to 17V and if it has current limiting set that to 1A, and attach the supply to the main reservoir capacitor observing the correct polarity. | |
| If all is well the receiver should fire up fully, and around 600mA or so will be taken from the supply.Flip the rig to transmit, and you should hear the clicking of relays, and another 100mA or so will be taken, though don't expect to get any RF out at this stage! |
A broken or burnt track was suspected at this stage, and I decided that I needed to get to the underneath part of the board for a closer inspection.
To get at the underside of the board there is no option but to unsolder a large proportion of the wires attached to the various pins, after removing numerous cable ties from the wiring harness which goes round two sides of the board.
There are at least 30 wires connecting to the pins on this board altogether, I opted to leave the HT cabling alone and disconnect the wires on the opposite side of the board from the HT cables allowing the board to be pivoted upwards through 90 degrees.
It goes without saying that you make careful note of which wires are removed and from where, I find my digital camera invaluable for this kind of work with the added bonus that it allows web sites to be created subsequently! You can see from the photographs what I found.
A crack in the PCB track exactly where I suspected it would be.
| Tip #2 | When you find one crack in a printed circuit board, there are usually others! |
I wish I had taken notice of this tip, as I omitted to look further than the obvious in this repair, and that meant that having repaired this problem, I still had another couple to go at!
I scraped away the PCB lacquer material and made a repair by jumpering across the broken track with a short length of stranded insulated wire. All the wires were reconnected, except that I opted for a more "ugly" way of doing this - where there are multiple wires going to the one pin, as in the 12V connections and the 0V connections, I joined these together away from the board and then just made one connection from the PCB pin to the collection of other connections. These were collectively sleeved.
I really don't like the idea of constantly re-heating pins on a board where you don't know what is going on under the board - a classic recipe for dry joints in my book! My solution looks quite ugly though, I have to admit. Yaesu developed this nasty habit of using PCB pins as makeshift tagstrip. Tagstrip was invented for doing precisely that.
So it came to testing time, and this is where I discovered that I hadn't cured the whole problem.
Further inspection of the board in situ and of my photographs made me realise that there was a series of cracked tracks (about four in all) more or less in a line, and this gave me a clue as to what may have been "root cause".
My guess is that a combination of the downward pressure from an over-tightened wiring harness, together with vibration from being transported plus the "less than perfect" quality of the PCB material used in these rigs resulted in a crack across a portion of the board.
I really didn't want to go to the trouble of unsoldering all those connections again, so I decided to take the easy way out and jumper round the breaks on the top side of the board - this actually rendered the 12V switching relay inoperable, but since this radio wasn't fitted with, nor was ever likely to be fitted with the dc-dc converter, then I decided this was going to be of no consequence. Still the end result was (eventually) a working radio, and which is still working.