alcoeddy
Newbie
There are several older (now closed) posts asking about this problem, none of which have elicited a sure fix. Symptoms are quite specific; AM bands will scan without stopping (regardless of whether squelch is open or closed); FM bands will either not scan, or will change frequency only once a second or so. NO sound, except perhaps for a brief burst of noise when changing between SVC bands. The symptom may be intermittent and appear to fix itself for awhile; the one I just repaired decided to work for a full day after misbehaving for a week, then failed again when powered down and back up.
I cheated a bit; had a working BCT8 handy to compare to the sick one. But hey, whatever works! The culprit is FT3, a ceramic filter located next to IC3 (the discriminator IC; this is a stealth-marked Motorola MC3361). This same filter or its direct equivalent is used in a bunch of scanner models; if it fails in them I would suspect that similar (but not necessarily identical) behavior occurs.
The filter's three legs connect to pins 3 and 5 on this IC, and to ground. IC 3 pins 3 and 5 should each read several megohms to ground; if the filter is sick, one or both will read 100Kohm or less. The part marking LT450DU is a good number, but you'll have trouble finding one. The Murata equivalent is CFU450D (don't ignore the D; it determines the 6dB bandwidth which is 10khz). I took a SFR450D from a junk Realistic Pro2026 to replace this one and it worked fine. The Pro2026 part is larger and has five legs instead of three (but the middle three simply all go to ground); it's found in lots of older Unidens (BC760XLT etc). The image below shows the sub part installed. Solder the middle three legs to each other, leaving one straight to insert in the PCB; one of the other two legs will line right up if you do this right, while the second will need to be lengthened a bit and bent to shape.
Wouldn't surprise me if FT4 can fail in the same manner (U450HT; same manufacturer, pinout and construction) but I do not know what symptoms would result.
I cheated a bit; had a working BCT8 handy to compare to the sick one. But hey, whatever works! The culprit is FT3, a ceramic filter located next to IC3 (the discriminator IC; this is a stealth-marked Motorola MC3361). This same filter or its direct equivalent is used in a bunch of scanner models; if it fails in them I would suspect that similar (but not necessarily identical) behavior occurs.
The filter's three legs connect to pins 3 and 5 on this IC, and to ground. IC 3 pins 3 and 5 should each read several megohms to ground; if the filter is sick, one or both will read 100Kohm or less. The part marking LT450DU is a good number, but you'll have trouble finding one. The Murata equivalent is CFU450D (don't ignore the D; it determines the 6dB bandwidth which is 10khz). I took a SFR450D from a junk Realistic Pro2026 to replace this one and it worked fine. The Pro2026 part is larger and has five legs instead of three (but the middle three simply all go to ground); it's found in lots of older Unidens (BC760XLT etc). The image below shows the sub part installed. Solder the middle three legs to each other, leaving one straight to insert in the PCB; one of the other two legs will line right up if you do this right, while the second will need to be lengthened a bit and bent to shape.
Wouldn't surprise me if FT4 can fail in the same manner (U450HT; same manufacturer, pinout and construction) but I do not know what symptoms would result.
