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New guy vs CR-840

Kirk V9 said:
Ok I got my replacement transistor for TR803 and all my capacitors in yesterday. Going to install 803 today.
Click to expand...
If you can fix it or not, it can still serve as a "tool" to hone your skills on. Soldering, desoldering, diagnosing, and learning. All of which are invaluable for the future.
 
Skywatcher said:
If you can fix it or not, it can still serve as a "tool" to hone your skills on. Soldering, desoldering, diagnosing, and learning. All of which are invaluable for the future.
Click to expand...

That’s exactly what I was thinking too. It will be a relatively cheap way for me to get some practice in. Admittedly, my solid state theory and schematic reading is definitely rusty.
 
TR803 has been replaced and it seems like some progress has been made.

I powered the unit on through the dim bulb tester and noticed different behavior. The power LED brightened a lot quicker rather than the previous behavior where it gradually brightened. I heard the relay engage and two of the lights for the FM tuning section (furthest two on the right) illuminated. After a couple of minutes I heard the relay disengage. I have tried turning the power on/off a few times without being able to get the relay to engage again.

Once again I checked my voltages for the power supply section:

Blue&Yellow: 21.4 VAC
Blue&Orange: 62 VAC
Yellow&Orange: 62 VAC

TR801 E: 43.4 VDC
C: 46.9 VDC
B: 43.9 VDC
TR802 E: -45.3 VDC
C: -47 VDC
B: 0 VDC
TR803 E: 0 VDC
C: 8 VDC
B: 0 VDC
TR804 E: 43.4 VDC
C: 46.9 VDC
B: 43.9 VDC
TR805 E:26.7 VDC
C: 27.9 VDC
B: 27.4 VDC

Voltages into tuning board

White: -46.3 VDC
Red: 7.4 VDC
Orange: 27.0 VDC

Fuses are still serviceable.

Any direction or advice is appreciated. Thank you.
 
Kirk V9 said:
TR801

B: 43.9 VDC

TR803

C: 8 VDC
Click to expand...

You either have a bad cap in the power supply or..... A bad solder connection on TR803.Or cracked circuit trace. The base of TR801 should be the same voltage as the collector of TR803.They are tied together in the circuit.
 
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Ok I reflowed the solder on 801 and 803. Here are the new readings:

TR801 E: 7.4 VDC
C: 53.8 VDC
B: 8.0 VDC
TR802 E: -46.2 VDC
C: -53.8VDC
B: -46.9 VDC
TR803 E: 0 VDC
C: 8 VDC
B: 0 VDC
TR804 E: -6 VDC
C: 46.9 VDC
B: -6.6 VDC
TR805 E:26.4 VDC
C: 27.5 VDC
B: 27.0 VDC

Tuner
White -46.2 VDc
Red 7.5 VDC
Orange 26.3 VDC

That seemed to fix the discrepancy between the base of 801 and the collector of 803. Same with the relationship between 802 & 804.
 
If you have caps in hand for the power supply. Replace them. Then recheck voltages around TR801 and TR803.This will eliminate possible suspects. Just make sure you observe proper polarity.
 
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OK Let’s try this again. I’m starting to feel stupid. o_O

TR801 E 29.1 VDC
B 49.5 VDC
C 29.7

TR803 E 0 VDC
C 29.6 VDC
B 29.5 VDC
 
Just do the C8xx caps right now. The large ones C826 and 827 can wait til later.They are for the unregulated rail supply voltages.
 
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Kirk V9 said:
What about the caps in the rectifier cct ? (C822-824)
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Personally I wouldn't even touch them. Those ceramic caps will out live you. For now just the electrolytic caps. Films and ceramic caps don't degrade/dry up like electrolytics do.
 
Replaced 8 caps in the power supply section on the board. C803, 804, 805, 806 809, 810, 811 & 812. All polarities were observed, the board markings made it easy.

No relay action yet. C902 in the protect circuit is definitely bulging on top.

More red LEDs Illuminated for the tuner section (Stereo, Blend, Local, DX, OTS) and both meters came to life but no lights.

Power supply Transistor readings:
TR801 E:29.6 VDC
C: 50.2
B: 30.1
TR802 E: - 46 VDC
C: - 50
B: - 46.7
TR803 E: 0 VDC
C: 30
B: 30
TR804 E: - 6 VDC
C: - 46.7
B: - 6.6
TR805 E: 23.1 VDC
C: 25
B: 23.7

The voltages for 801 B & 803 C still match and have come up in volts but still not quite 42 volts.
 
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Kirk V9 said:
Replaced 8 caps in the power supply section on the board. C803, 804, 805, 806 809, 810, 811 & 812. All polarities were observed, the board markings made it easy.

No relay action yet. C902 in the protect circuit is definitely bulging on top.
Click to expand...
Replace the bulging cap, and any other that you find that are bulged or suspect.
 
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