A month or so ago an acquaintance of mine within the local amateur community asked me to try his radio – a Yaesu FT-one thousand MP Mark V. While I do not routinely repair other folks’s radios, I decided to make an exception, as I’ve known this gentleman for many years.
The complaint was “The receiver is useless” – which is a really broad evaluation, but it surely was an apparent place to begin and upon putting this relatively large, ponderous piece of equipment on my workbench – which, itself proved to be a challenge – I famous that it took a few 0dBm signal to attain an “S-9” reading: Yes, the radio was deaf, to the tune of round 70dB! Knowing that the antenna A/B relay and/or antenna tuner could be an issue with this particular radio, I tried completely different configurations – even the (in a different way-routed) rear “RX Antenna” jack – however no difference.
This radio’s technology and construction is what I’d check with as “transitional” – largely paying homage to 80s Japanese radios in that there is a mix of through-hole and surface mount, and the boards are mostly interconnected with a myriad of white wires with unmarked plugs on them that go in every single place in the case – with the occasional gray coaxial cable that use the odd board-mounted plug-in cables. Fortunately – unlike a few of these older radios – the boards are principally double-sided epoxy somewhat than single-sided paper phenolic.
In fact, the main receive RF board was buried under the very large heat-sinked power amplifier meeting, so I first did a take a look at on the “sub” receiver board, which was accessible: That receiver seemed to be moderately delicate once i injected a signal straight into it, but there was no sign of RF getting to that receiver via the radio’s rear coaxial cable connector.
The following, obvious step was to take away the PA board – which, like many issues about engaged on this radio, was a real pain: Only 4 screws, but two of them had been buried underneath a mass of white wires – I pulled the amplifier module out from the radio with trepidation, figuring out that I’d finally must get it again collectively.
A visual and an olfactory inspection of the receive board – before eradicating it – was accomplished, and nothing was obviously amiss, so I removed a bunch extra screws and cables – marking them as acceptable (you’ll hate life if you don’t mark the place they went as you take away them!) I used to be ready to pull the board away and immediately noticed the primary indications of the problem: A really apparent black mark on the aluminum chassis underneath the board and power generator a corresponding area of char on the board itself (see Figure 1, above and Figure 2, beneath).
What may need happened:
Knowing that this was not prone to be the one drawback, I half-put in the board once more and checked the receiver: Very slightly much less terrible – but nonetheless deaf as a publish, but with access to the board, I cranked up the signal generator to zero dBm and started poking round with the oscilloscope to see where RF disappeared.
Initial re-testing:
Putting the board back in, quickly, I re-checked the receiver sensitivity and found that it was “Ok”, in that I may contact a screwdriver and put it within the rear-panel RF connector and listen to alerts, however a fast check with the signal generator indicated that one thing was still amiss as it gave the impression to be off by about 15dB based on the specs within the alignment procedure.
At this point I determined to check the transmitter and to my gratification, I used to be capable of get about ninety watts out of it. My preliminary satisfaction was short-lived, as I quickly realized two three things:
– I ought to have been in a position to get at least a hundred and fifty watts out of the transmitter.
– The SWR indicator on the radio was exhibiting a mismatch, with the tuner bypassed, right into a known-good load.
– I smelled epoxy smoke from the “RF Unit”.
At this point I once more removed the RF unit and replaced D1056 (again!) – the obvious source of the smoke that I’d smelled and – without transmitting – restored the operation of the receiver. In reviewing the service guide and online boards, I discovered that the failure of RL6414 was semi-frequent, and also that this particular relay – seen in Figure 4 – was troublesome to source. Nevertheless, I despatched an e mail off to Yaesu Parts to search out out.
A number of days later I’d heard back from Yaesu: This relay was available – however it might take 6-8 weeks. Within the meantime I’d tried to seek out an exact substitute elsewhere, however to no avail: The original relay had a non-commonplace pin-out and was a brand that was merely not carried by U. If you have any inquiries regarding where and how you can use backup prime diesel generator generator (devpost.com), you could call us at our own web site. S. elements suppliers – and I could not make sure if this significantly relay was still made! In talking with the owner of the radio I gave him two choices: Order the half and wait 6-eight weeks, or get a extra frequent part and adapt it to suit: He opted for the latter, so I placed an order with DigiKey, set the radio apart and waited.
It’s worth noting that RL6414 is an SPDT relay with the RX sign path related within the “Normally Open” position with the “Normally Closed” place grounded – that is, the relay must be energized for the receiver to be connected to the antenna. If the radio is turned off, there isn’t any direct path, so whatever “killed” the receive, must have both occurred with the radio turned on, whereas it was receiving, or it was sufficiently energetic sufficient to weld the relay and, apparently, blow away the bottom “N.C.” contact: Yet more proof of a “high vitality discharge” from lightning.
Resuming work:
At this point, I will be aware again how troublesome it is to work on this radio – highlighting, on this case, the antenna tuner. This module consists of two boards, face-to-face, which means that no parts are accessible until they are separated. Unfortunately, there are several wires that seem to have been pulled via from the “lower” board (with the tuning capacitors) after which reduce quick – and none of the other wires have been any longer than they absolutely needed to be. Disassembly was fairly simple (especially with correct desoldering equipment) but re-soldering the brief wires was an train of patience and the careful manipulation of small tweezers and screwdrivers to try to align all of the wires simultaneously without causing a number of of them to pop out of place!
Alignment – and more problems:
Not having part of the transmitter sign path in parallel with the receiver enter helped the sensitivity a bit, but it surely still wasn’t right so I did a bit more checking with the signal generator and scope, finding no-where that issues were clearly amiss on the RF Unit – however I did notice that the secondary receiver was more delicate than the primary: Since they share the same sign path that roughly ruled out an obvious downside with the RF unit when operated in the traditional style so I determined to perform a realignment.
To my surprise, the I.F. I used to be surprised to see this on a modern receiver. Am at a loss to elucidate it. It appears unlikely that it detuned itself with age, so it was both not correctly aligned on the factory, or another person tried to “improve” it – however I’m suspecting the former.
In performing the alignment steps, I then “discovered” that the “VRF” circuit – an electronically-tuned preselector – was inoperative, about 25 dB of excess attenuation: This problem was traced again to being brought on by RL1005 having welded contacts, not allowing this preselector circuit to be absolutely switched into the sign path. This not unexpected as this is in the identical sign path as the vaporized trace and capacitor. Fortunately, these exact relays were readily out there from Digi-Key as nicely. The alternative of RL1005 turned out to be the final drawback that was found. The radio easily met its specs when the job was performed. The reassembly of the radio was, as expected a little bit of a challenge: The inboard mounting flange of the PA unit shares the same channel as dozens of thin, white wires and there may be practically no visibility as one tries to maneuver the screws into place while making an attempt to keep away from them getting knocked off the magnetic driver while, at the identical time, making an attempt to make sure that none of the dozens of small, white wires get pinched in the method – all the whereas attempting to align to invisible holes!