mike stehr Posted November 8, 2016 Author Share Posted November 8, 2016 Finally ordered the necessary caps to replace the tantalums, along with some 6.8uF (10 or 16volt) non-polarized caps...and some panel bulbs. Couldn't find 6.8uF NP caps at Mouser...at least in lower voltages. I picked up Wima polyester 50 volt radial film caps to sub instead... The tuner board had a dirty nasty capacitor...it was a decoupling cap from the looks of the schematic to part of the tuner I guess. The tuner pulled in stations rather strong with no drift, but was noisy. 1 Quote Link to comment Share on other sites More sharing options...
Wim M Posted November 8, 2016 Share Posted November 8, 2016 1 Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 9, 2016 Author Share Posted November 9, 2016 I'll trade ya... Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 14, 2016 Author Share Posted November 14, 2016 Okay, I have the receiver working...it doesn't sound weedy/grainy anymore. The unit has a more of a modern amplifier/receiver sound. Hard to explain, but the amplifier section of the receiver sounds rather good. I was playing Die Antwoord with a CD through the AUX input...it seems a conservative rating at 20 watts per side. No need for the loudness button, or pushing the bass pot past flat. With the tone pots set flat and no loudness button, the bass is strong and deep through my Cornwalls. Rather impressive bass depth for a wimpy '70's era receiver...I noticed that even before the recap. Image of a 3.3uF (10v?) Tantalum cap, next to a Nichicon sub-mini 3.3uF 35 volt 'lytic. The 0.47uF Tantalums were replaced with Elna Silmic II 35 volt caps. The only bummer is now the FM beacon light doesn't work, (and the bulb is not burned out) along with the FM mute switch not working. From looking over the schematic and the circuit, all paths lead to a 14 FM stereo demodulator. NEC UPC554C creepy crawly... I may have got dumb and overheated things around the IC, along with the fact the bottom of the tuner board traces look crusty and nasty in spots...I may have zapped pin 5, and 6 of the demodulator chip. Maybe a trace got disconnected... The NEC UPC554C is still around in NOS form, and on eBay for ten bucks or less. I still can get FM stations okay, and I'm sure the signal is still in stereo. But it seems a bit more dodgy pulling the stations in, with some noise while not as bad as before. Along with the lack of beacon lamp and non-functioning stereo mute switch. Temped to buy another UPC554C, carefully rig up a 14 pin socket with a couple 8 pin sockets, (if I can find them around here) and swap it in knowing I won't burn it soldering. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 14, 2016 Author Share Posted November 14, 2016 I used a combination of Nichicon Muse and Elna Silmic II. I swapped the ceramics in the PS for CDE polyprops. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 14, 2016 Author Share Posted November 14, 2016 Bypass caps for the PS caps. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 14, 2016 Author Share Posted November 14, 2016 Pre-amp board with tone controls, etc... The sub-mini 'lytics around the bass pot where the tants were. I goofed and ordered 6.8UF polarized caps for input coupling, and all Mouser had was the Wima polyester caps...still better than a 'lytic I think... I goofed again, and ordered too low voltage caps for the Op-amp, so I scrounged some Nichicon VX axial caps to use. Check out the Raytheon vintage 4558 metal slop amp... Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 15, 2016 Author Share Posted November 15, 2016 Thanks. As DJK would say...Like roaches you gotta get 'em all. Quote Link to comment Share on other sites More sharing options...
mike stehr Posted November 24, 2016 Author Share Posted November 24, 2016 Argh...so I bought four FM stereo demodulator ICs, (why buy one for 10 bucks when you can get four) pulled the tuner board, tore out the old IC, soldered in a 14 pin socket, and tossed in a NOS IC. Still no functioning stereo beacon lamp. Check over the voltages to the chip...everything checks out except pin six...the stereo beacon lamp. 500 millivolts where it shouldn't be more than 22 millivolts max. Then I started to examine the stereo beacon lamp more closely. My eyesight isn't the greatest anymore, and I should have paid more attention. Broken filament! Oh well. I learned some things about stereo demodulators in the process. I also checked over the bias for each side of amplifier section. It calls for 30ma. (.47+.47) X 30 milliamps= VOM # in millivolts. .94X30= 28.20 millivolts. I have both sides around 28.5 volts. When I first measured the bias in millivolts, one side was 5 millivolts and the other 8 millivolts. Dunno why so low... After readjusting the bias, this is when the receiver sprung to life. Re-capping the receiver got rid of the weedy/grainy dirty sound and improved things. But a good re-bias really makes a notable difference. (with regard to this unit, IMO) So I just need a little sub mini 8 volt 50ma beacon lamp, and this receiver should be good to go. The girlfriend has been wanting a good clean sounding, easy to operate vintage receiver with good reception for the Cornwalls for when I'm not home. I think I managed to pull it off...but she is picky. Mike Quote Link to comment Share on other sites More sharing options...
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