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Kenwood KR-5400 - Weak Output / Blowing transistor [ repair help]

Good call rickl! Not a done deal yet, but I wiggled that quad switch around and bam, got loud/dim bulb tester started throbbing with the music. So something is weird in that switch. I've already put the new 6800 uf power caps in yesterday and put in new power transistors today (before I wiggled quad switch). The bias jumped up on right side to 40+ volts which I put back to 20v via the pot. Left side bias still at -0.7mv with the pot turned all the way, not sure what's going on there. I'll get back on it tomorrow/clean that quad switch see what happens.
 
Bingo! Quad switch had a wire loose/came off when I pulled switch from frame. I never plan to use 4 channel so I bypassed the switch permanently. The thing is working great now, but there are still a few issues. The stereo beacon light does not come on/ has no voltage, even when on a strong FM stereo station. I relamped it, so not sure what's up with that. The bias is still at -0.7mv on the left (with pot maxed out) and a steady 20mv on the right. The OP mentioned replacing 3 bias transistors (Q7,Q8,Q25) which I haven't done yet and may very well be why I'm getting bad reading on the left side. Is there a way to test them while still connected to the board?
Thanks in advance,
Nordo47
 
Stereo beacon light now working. It just needed slight tweaking of the pot (Vr2) near IC SN76115N. Still debating on changing out 3 bias transistors Q7,Q8, and Q23. On the one hand it sounds good now, on the other hand I'm trying to learn new stuff/need the practice..... Thoughts from AK land?
 
rickl said:
Leave it if it works.

Enjoy the music.
Click to expand...
Been doing just that until today. Turned it on and nothing at 98.5 my usual station. Fiddled around with it and it works as advertised on some other stations with stronger signals, stereo light and all. So I'm thinking maybe that station is off air? Negative there, works fine on car radio. Went back in garage and discovered that if you turn off FM Muting it comes in but no stereo signal, sounds a little scratchy. Been working fine for 9 months until today. Ideas?
 
I think it might be the antenna. It's one of those T type antennas made out of flat wire. What is a good antenna so I can eliminate that as a possibility? Is there a way to test an antenna with a meter?
 
Cleaned the tuner and it's picking up my usual station again, but the crappy "T" antenna has to be positioned in just the right spot for that. I ordered a yagi antenna to put up in the rafters above my bench in the garage. It is 75 ohm that has coax connection. The rear of the KR-5400 only has the screw down lugs for flat cable. All the little transformers I've seen to go from type F coax connection to the spade (flat lugs) connections say 75 to 300 ohm transformer. My new antenna and the coax cable both say 75 ohm, so I don't want to be transformed back to 300 ohms. I guess I'll just strip the coax and put the braided outer shielding wire on the"GRD" lug and the center solid wire on the 75 ohm lug. That "sound" about right?
 
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