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CR-2040 hot resistor issues.

Vince1966

Vince1966

AK Subscriber
Subscriber
I picked up a working CR-2040 that is filthy and running with High DC At the speaker terminals. So far I have cleaned the pots and switches and started cleaning everything else. Adjusted Idle current and DC Offset Baxter to where they need to be. I am looking over the boards for cold/bad solder joints and have noticed a rather large hot spot Where R-657, 648, 659 and 670 are soldered on the tone board. They are buried under the wiring and lacks good airflow. Has anyone addressed this issue and any other hot spot issues with the 2040? Seems to be a good candidate for relocation of the larger resistors for better cooling our upgrade them. There are a few other spots on the tuner board, see pictures.


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Was running +285mv on the left and +1.090 vdc on the right. DC offset and Idle current was +63mv right and +29mv left. Power section was running +65.3vdc, readjusted to 60.2vdc I think the last owner tried to adjust it and gave up with all the other problems like burned out lights and severely dirty selector switch that made it appear that the right channel was distorted. Sounding very good now.
 
Wasn't the 2040 the ONE CR-x40 series receiver that escaped the STK chip amp and bloody pre-driver chips? I think it is. I like the look of the x40 series better than the x20 series but prefer the x20 series for their serviceability. I've repaired a few of the x20 receivers including my own CR-2020. Had a really nice CR-840 that was working well and gave to my mom. Have another CR-840 that has blown outputs on the shelf waiting to be repaired. But that CR-2040 you have is SWEET!
 
avionic said:
Whats it running after adjusting the DC offset ?
Click to expand...

it’s running 5.4mV left and 7.3 mV right. The trimmers are soooo sensitive. I plan on replacing them with sealed Bourns multi turn trimmers down the road to get it dialed in better.
 
Vince1966 said:
it’s running 5.4mV left and 7.3 mV right. The trimmers are soooo sensitive. I plan on replacing them with sealed Bourns multi turn trimmers down the road to get it dialed in better.
Click to expand...
Probably won't get much better than that..
 
Nakmandan, from what I’ve read it’s one of the few XX40’s that have discrete outputs, that’s a good thing, I avoid STK chipped gear.
 
Avionic, your right, Hard to get much better than that, but I noticed today when I rechecked the settings they drifted a bit so I’m thinking the trimmers are dirty and need to be replaced.
 
I had a good pop in my test speakers, most of it is now gone after setting the offset. I’m waiting on bulbs from Dave to get that solved. Main concern is having those large resistors close together and confined, it’s starting to discolor the board and solder.
 
Vince1966 said:
it’s starting to discolor the board
Click to expand...
Those are 1 & 2 watt resistors.. And the discoloring took place over 40 years.. They drop the +/-60v down to +/- 24 and +/-12v..Larger wattage resistors will still run just as hot but will provide more surface area to radiate the heat.
 
Vince1966 said:
Avionic, your right, Hard to get much better than that, but I noticed today when I rechecked the settings they drifted a bit so I’m thinking the trimmers are dirty and need to be replaced.
Click to expand...
Within + or - 10mv is factory spec.
 
Thanks for the clarification Avionics. I will spend part of the day doing some detailed cleaning and run it for a few hours to see how it settles. Plan is to eventually replace the trimmers and recap the unit down the road. I will start another post for that.
 
So this is the issue, when cold the right channel starts at +580mV then drops to +23-, +18 mV after a few moments. Left is -230mV and settles to around -9mV. When the relay clicks they are both high and gives a nice little pop, yesterday they were good after adjusting them in. Idle setting are good from cold to warm. Any Ideas there? Normal? Or should I be looking for Fuse resistors going bad? I need to look over the schematic and find them.
 
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