When I had a need for some 2 way 446MHz Radios for camping I considered the local off the shelf rigs but decided I would go for the big brand Motorola TLKR-T3.
The radios have had minimum use but they are handy for the times when we need them, unfortunately one of the radios stopped receiving so I decided to take a look at it. It is always good to Google the problem, I did, there are several queries the only replies are ME TOO, lots of them.
There are no offers of help, no cures, no circuitry available, not even a layout diagram.
Being cheeky I asked the Director of a PMR repair company the question, 'Motorola have a problem any clues as to what it is please'. What a grand fellow he is, he replied on a Sunday, it seems that the 450KHz filters die like flies, he put his guess at 99.9%.
With that information I looked up the filter type No. CQ WM50HTd on Google, it is 450KHz BTW. Here we go again one poor guy has a set of four of theses rogues, one day when they were needed 3 of them had thrown up the same fault, no receive, and yes it was the filter in each one.
A bit of extra information was revealed by him too, I hadn't noticed, remove the rubber keypad and the PCB is marked Uniden the true Chinese producer.
The 450KHz filter a screen and 2 Xtals are fitted by hand soldering, in the radio with no receive the soldering was disgusting, component leads were blackened the joints dry looking with vast amounts of black clinker around them.
I opened the radio with no problems, the majority of the hand soldered joints looked OK, however an HC49 Xtal had been thrown at the PCB it stood high at one end its lead resting unsoldered on the gold pad on the component side, the other lead just made it through to the underside where a dome of solder was placed, I gently touched the Xtal and it merrily rotated on its one nearly soldered lead.
So much for Motorola's brag of extended life vibration testing.
OK so lets look up the filter, Google is our friend they say. Not for this kiddy, no listing no data, no connection diagram, no indication of equivalents (the pinning will most probably be different) its not even clear who makes it, maybe the CQ indicates Chequers Electronics in China, they say they supply into Eastern Europe not the EU.
I wonder if there is a way into the Motorola closed shop for spares.
I find it interesting that some Ham Transceivers have problems with 455KHz Ceramic Filters often the wider FM ones, the Yaesu FT857/FT897 suffer I am told. It is said that the cause of failure is electromigration, I have it on very reliable authority that this is not the cause.
How about cheap copies of decent filters by some obscure set up in China manufacturing in a non ideal environment, somewhat like the soldering process used to fit them.
The actual CQ WM50HTd remained illusive so I intensified my search, there is a Polish EBay seller who has Murata equivalents from his illustrations it looks as if they have changed the size and pinning of the latest ones, CFWLB450KHFA to match the CQ pattern. I have nothing against buying from Poland but it may take time and the postage is five times the price of the filter. I could buy them from a distributor in the UK but I want one not 1,000.
Previous Murata filters are in the CFWM450B to CFWM450I range slightly larger and with different pinning. I found an EBay seller in Wales who has some CFWM450B's, the B/W of these is too wide. However this will merely give us more audio B/W and maybe a bit more noise, if these were Yaesu Transceivers I would want it right, but with these,do I care? Additionally a strong signal on an adjacent channel could open the squelch or we may hear splatter again do I care? Actually to hear someone on our travels would be a minor miracle.
So for the sake of £3.50 including postage (it arrived next day) I took a gamble. The CFWM450b is physically a bit too wide but it fits in the gap, the input pin is on the wrong side, the pinning is 1 pin on the left 4 on the right, the original is 2 on the left 3 on the right so I had to cut the input pin down and put a wire link across underneath to the hole for the pin. The CFWM450B stands a little higher than the original and once you have fitted the wire link it sits a little bit higher still, there is room if it wasn't for a small reinforcing web in the plastic back casing, that was easily chopped back to half its depth and the case half fits fine.
On test, sure enough the repaired one is louder than the original and the squelch comes up when the other TX is keyed up in the same room on an adjacent channel, performance is however fine for what we want and probably for longer range too.