let say about the price I spent ( hobbyist and fun):
* Left channel is silent (from the collector, mostly pristine with some minimal scratches) = $102 with shipping <- CR-840-1
* Left channle is silent or was this a coincidence
( I would say grade B/C, some corrosion from salt water underneath shield and front face including lower part cover expanding due to water contamination) $95 with shipping. <- CR-840-2
* Suddenly seeing pre-driver NoS new (authentic) $40 after negotiation. the seller knew how rare is this ha....
Total is $237
CR-840-1 is in a "very" good shape. the previous owner gave up and removed the broken pre-driver but damaged some PCB traces
but actually, right pre-drive is flaky, sometime working and sometimes not ...
CR-840-2 is ok and can be refurbished (with metal/oxidation polish and including sanding the bottom panel to remove corrosion and repaint metallic spray)
CR-840-1
Soldering NoS and CR-840-2 pre-drive of working channel to CR-840-1 . not forgetting to add big heatsink on pre-drive without heatsink can go up to 50C with open lid <grazy, Yamaha should Add heatsink on pre-driver>, with heatsink is hovering 36-40 depending on how loud the volume is.
Set the bias to let the VDC speaker ouput to 0 - +- 5mv :-D, need extra time due to trimmer sensitivity (already de-oxit too).
Replace pre-driver capactor with nichicon UKZ. hard to replace when heatsink added just in case.
CR-840-2
Left channel outputing +45V DC, seeing one of 5 W resistor is cracking without heat damage residue, it is just crack one of the pin aka open circuit. My prediction the pre-driver is ok, ordering 5W resistor (surprising, cheaper buying from amazon prime and one day delivery today)
Right Channel is ok ( remove pre-driver and transplanted CR-840-1).
* bought 2950 from CR-640 $16, it the voltage is identical, but for power module is different: 640-> 41V and 840 -> 48V ( CR-840 schematic said 41V and wrong, but correct for pre-driver)
planning to restore CR-840-2. if not make it, I will take pre-driver and power module as spares and replace with chinese amp module L20 V10 hehehe. $44 for two board.
next plan: replacing caps
Heatsinks are required
the donor, it works but broke left channel. the pre-driver is flaky, from the main CR-840
The Donor, I just cleaned up the radio side, and quick clean up on the amp side
the main CR-840 that already working order, and waiting for recap
The main CR-840, thanks to the previous owner whom maintained the unit.
* Left channel is silent (from the collector, mostly pristine with some minimal scratches) = $102 with shipping <- CR-840-1
* Left channle is silent or was this a coincidence
( I would say grade B/C, some corrosion from salt water underneath shield and front face including lower part cover expanding due to water contamination) $95 with shipping. <- CR-840-2* Suddenly seeing pre-driver NoS new (authentic) $40 after negotiation. the seller knew how rare is this ha....
Total is $237
CR-840-1 is in a "very" good shape. the previous owner gave up and removed the broken pre-driver but damaged some PCB traces
but actually, right pre-drive is flaky, sometime working and sometimes not ...
CR-840-2 is ok and can be refurbished (with metal/oxidation polish and including sanding the bottom panel to remove corrosion and repaint metallic spray)
CR-840-1
Soldering NoS and CR-840-2 pre-drive of working channel to CR-840-1 . not forgetting to add big heatsink on pre-drive without heatsink can go up to 50C with open lid <grazy, Yamaha should Add heatsink on pre-driver>, with heatsink is hovering 36-40 depending on how loud the volume is.
Set the bias to let the VDC speaker ouput to 0 - +- 5mv :-D, need extra time due to trimmer sensitivity (already de-oxit too).
Replace pre-driver capactor with nichicon UKZ. hard to replace when heatsink added just in case.
CR-840-2
Left channel outputing +45V DC, seeing one of 5 W resistor is cracking without heat damage residue, it is just crack one of the pin aka open circuit. My prediction the pre-driver is ok, ordering 5W resistor (surprising, cheaper buying from amazon prime and one day delivery today)
Right Channel is ok ( remove pre-driver and transplanted CR-840-1).
* bought 2950 from CR-640 $16, it the voltage is identical, but for power module is different: 640-> 41V and 840 -> 48V ( CR-840 schematic said 41V and wrong
, but correct for pre-driver)planning to restore CR-840-2. if not make it, I will take pre-driver and power module as spares and replace with chinese amp module L20 V10 hehehe. $44 for two board.
next plan: replacing caps
Heatsinks are required
the donor, it works but broke left channel. the pre-driver is flaky, from the main CR-840
The Donor, I just cleaned up the radio side, and quick clean up on the amp side
the main CR-840 that already working order, and waiting for recap
The main CR-840, thanks to the previous owner whom maintained the unit.