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Alan Bain · 30th May 2022, 10:17 pm

Thanks to moderator for reopening! So I also have a TR4172 which is deaf 35db and interestingly the voltage measurements in the IF1 amp match those reported by Lex in #24 above (110mV CE of the RF device, and VTP3 around 7V instead of 10V, current draw from 15V supply 22mA). There was a black blob of epoxy over bias device and attempting to gently scrape this pinged off the device and a small capacitor to earth off to infinity and beyond, fortunately with minimal track damage. I have no idea what the capacitor value was but appears connected base to earth of the biasing transistor. Does anyone have any idea?

Fortunately no blobs of glued on absorber and no signs of track damage. This is an early Takeda-Riken badged model.

My resistors all look good and measure
R1=2180 ohm
R2=406 ohm
R3=10K
R4=4K7
R5=436 ohm

I imagine that a generic PNP SOT-23 like a BC857 should do - does anyone have any advice on what to use both as equipment and as solder for soldering it (I have a stereo microscope)? I'm not familiar with this sort of almost hybrid like board with chrome and gold layers.

30th May 2022, 10:17 pm	#178
Alan Bain Pentode Join Date: Jan 2012 Location: Heswall, Merseyside, UK Posts: 177	Re: Spectrum Analyser TR4172 Thanks to moderator for reopening! So I also have a TR4172 which is deaf 35db and interestingly the voltage measurements in the IF1 amp match those reported by Lex in #24 above (110mV CE of the RF device, and VTP3 around 7V instead of 10V, current draw from 15V supply 22mA). There was a black blob of epoxy over bias device and attempting to gently scrape this pinged off the device and a small capacitor to earth off to infinity and beyond, fortunately with minimal track damage. I have no idea what the capacitor value was but appears connected base to earth of the biasing transistor. Does anyone have any idea? Fortunately no blobs of glued on absorber and no signs of track damage. This is an early Takeda-Riken badged model. My resistors all look good and measure R1=2180 ohm R2=406 ohm R3=10K R4=4K7 R5=436 ohm I imagine that a generic PNP SOT-23 like a BC857 should do - does anyone have any advice on what to use both as equipment and as solder for soldering it (I have a stereo microscope)? I'm not familiar with this sort of almost hybrid like board with chrome and gold layers.