guy232
Member
R-70 Service Manual: https://docdro.id/P9uWhrM
Started this project with zero experience with electronics/repair. Did research via google, youtube & forum searches and bought the tools i'd need to re-cap the entire main PCB on this unit. A majority of the caps showed signs of leaking/discoloration so I thought it may be worth using this unit as my first project.
Everything went pretty well, spent a lot of time off & on learning various things. Completely disassembled the unit including the heat sink. Cleaned the boards up a bit, installed all of the new caps, installed new AC cord, re-assembled everything, all parts accounted for.
Only main issue encountered was that the filter caps I bought were too large so I had to extend the leads. Used some heavy gauge insulated solid copper wire to extend leads, then fabricated up 2 rubber stands, applied adhesive to give the caps support.
Plugged into DBT (150W bulb), very faint brief glow of filament which quickly went away. Unit was operational.
Plugged into wall socket, powered it up and started taking voltages as suggested in the service manual, findings recorded below.
I'm not too sure how complete the other service manual tests such as Gain, DC Offset, and Phono Amp but I am reading into it.
I noticed that the L channel speaker terminals have higher mV when tested in both A & B speaker sets. The mV is still super low based on what I read, maybe I don't need to address the slight difference in mV?
Any other suggestions on what to test for that the service manual may have not mentioned?
Power Supply Voltage Measurements, No Load:
Blk probe grounded to chasis, Red probe touching each point on main board set to DC V 200 range:
+B: 45.3V [+43V ±8V]
-B: -45.3V [-43V ±8V]
+16: 16.4V [+16V ±2V]
-16: -16.9V [-16V ±2V]
+12: 12.3V [+12.5V ±1V]
+5: 5.7V [+5.5V ±0.5V]
+8: 7.8V [+8V ±1V]
-8: -7.7V [-8V ±1V]
DC Voltage at speaker terminals, No Load
B & R Probe inserted into + & - speaker terminals, set to DC V 200m range
A/B (Both A & B had the exact same readings)
L: -2.9 mV
R: -1.2 mV
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