cr2040 no output. slight hum

TheCodeDawg

TheCodeDawg

New Member
I recently stumbled upon a cr2040. Spec wise, it is similar to my beloved sx1050, so I was intrigued and bought it from the Goodwill. It's a beautiful machine for sure. I ran home and plugged it into my dim bulb tester with no load on the speaker ports. Uh oh. What's that buzzing sound? The protection relay was opening and closing a a rate approaching 60hz. Off to hifiengine for the service manual. Out came the Fluke MM. First, an inspection of the power/speaker board showed a split resistor. The MM showed 2 bad switching diodes. I also removed the relay. The solenoid works fine and the resistance was .1ohm with the contacts closed. Put it back in and fired her up. No more chatter from the relay. And I had plugged in speakers. But wait. Since when does a protection relay open with the power switch? It also had the loud pop when turned on and off. (Note: ALL the lamps were fried) I groked the forums for this issue and found lots of advice. I replaced the 100, and two 33uf caps and the 3 npn and 1 pnp transistor. (Many thanks to Luddite Electronics in Longmont, CO for having them in stock) Now the protection relay works properly and no popping sounds at start and stop. however...

There is no output to the speakers other than a slight hum. Also, there is a popping sound followed by the protection relay opening. The 1/2 power and overload LEDs flash as well. I am not sure where to begin trouble shooting this. I also have an oscope. HELP!
 
What position is the coupler switch in - it is on the back panel. In case the switch is dirty use interconnects to feed pre out to main in.
 
merrylander said:
What position is the coupler switch in - it is on the back panel. In case the switch is dirty use interconnects to feed pre out to main in.
Click to expand...

Rob
The CR-2040 does not have a coupler switch.No pre-out/main-in provisions.
 
TheCodeDawg said:
I recently stumbled upon a cr2040. Spec wise, it is similar to my beloved sx1050, so I was intrigued and bought it from the Goodwill. It's a beautiful machine for sure. I ran home and plugged it into my dim bulb tester with no load on the speaker ports. Uh oh. What's that buzzing sound? The protection relay was opening and closing a a rate approaching 60hz. Off to hifiengine for the service manual. Out came the Fluke MM. First, an inspection of the power/speaker board showed a split resistor. The MM showed 2 bad switching diodes. I also removed the relay. The solenoid works fine and the resistance was .1ohm with the contacts closed. Put it back in and fired her up. No more chatter from the relay. And I had plugged in speakers. But wait. Since when does a protection relay open with the power switch? It also had the loud pop when turned on and off. (Note: ALL the lamps were fried) I groked the forums for this issue and found lots of advice. I replaced the 100, and two 33uf caps and the 3 npn and 1 pnp transistor. (Many thanks to Luddite Electronics in Longmont, CO for having them in stock) Now the protection relay works properly and no popping sounds at start and stop. however...

There is no output to the speakers other than a slight hum. Also, there is a popping sound followed by the protection relay opening. The 1/2 power and overload LEDs flash as well. I am not sure where to begin trouble shooting this. I also have an oscope. HELP!
Click to expand...

Check that all the regulated and unregulated power supply voltages from the power supply to the amplifier assemblies as well as the EQ flat amp circuits are present and close to the posted values on the schematic.Check solder connections on the power supply regulated pass transistors.( TO-220 transistors with little square heatsinks)
 
Last edited:
voltages

attachment.php


The voltages are identical on both sides.
 

Attachments

  • cr2040leftampvolts.jpg
    cr2040leftampvolts.jpg
    66.7 KB · Views: 69
TheCodeDawg said:
attachment.php


The voltages are identical on both sides.
Click to expand...

Looks like the +/- 60vdc regulated power supply shit the bed. Check Solder connections on the power supply circuit board, as well as fuses. Use a meter to check fuses.
 
Last edited:
It's alive! ALIVE!

I replaced both regulators. We have sound!!. However, it's all treble. The left channel has very distorted bass and the right has none. The distorted bass on the left channel "kicked" in after turning the volume up and down a couple of times I deoxed all the pots and switches. BTW. The trimmers for the DC offset are very very touchy.
 
"channel "kicked" in after turning the volume up and down a couple of times"

To me that sounds like a classic indicator of contact problems in the protection relay. You could try disassembling the relay and burnishing the contacts if you have a suitable tool. Or replacing the relay.

Just passing through. No specific CR-2040 experience, myself. Cheers,

chazix
 
not the relay

"channel "kicked" in after turning the volume up and down a couple of times"
Click to expand...

Sorry to be confusing. Both channels produced sound immediately when the relay activated. However, there was no bass on either channel. Only treble. I adjusted the base dials with no change in sound. Then I turned the volume up and down (no more than a quarter) when the left channel suddenly produced very distorted bass. As part of the original relay issue, I cleaned and tested the relay. It's in great shape. Good continuity, no resistance, shiny contacts, and the solenoid works flawlessly
 
based on the fact that you had a cracked transistor, I'd guess you aren't done replacing failed components yet. Whatever caused that cataclysmic failure likely caused more damage elsewhere.
 
Whoops, apologies for my reading comprehension!

A stepwise change in symptoms still sounds like a contact problem to me, but if we assume that it's NOT the relay, pots, or switches, I'm afraid that leaves nothing on my list of "usual suspects".

Perhaps time to employ your 'scope? Both the distortion and the disparity between channels should be pretty visible. I'd start by comparing the left and right channels at the tape monitor output jacks, then compare again at the high side of the volume pot (or maybe the pre out jacks), then at the inputs to the power amps, then at the outputs of the power amps. With luck, you'll be able to localize at what stage the distortion/disparity creep in.

chazix
 
Do you get the same distorted sound with the "Presence" control centered? Turn the (Loudness,Base,Presence & Treble) to the "flat" position. Any difference?
 
Last edited:
The fact that both channels are distorted. Still points to a power supply issue. Its the only thing common to both channels. Can you post a photo of the power supply area ?
 
Last edited:
I pulled and tested all the transistors on the right power amp board. I need to find replacements for 2sc716a, 2sd756a, and 2sa1015. Any suggestions?
 
2sa1015----------ksa1015
2sd756a ---------ksa1220A TO-126
2sb716a ---------ksc2690A TO-126
 
Last edited:
You must log in or register to reply here.

Similar threads

Soundcraftsmn
yamaha CR 2040 power on issues
Replies
9
Views
2K
batts
batts
Pauln
Help with CA-600 - relay and loud hum
2
Replies
33
Views
3K
Pauln
Pauln
G
Yamaha CR2040 died while changing lamps
2
Replies
27
Views
2K
Pio1980
Pio1980
Raccoon1400
Yamaha CR-1010 no relay click.
2
Replies
22
Views
2K
avionic
avionic
Thespeakerdude8
Ca-810 oscillating protection relay pulling my hair out
2 3 4
Replies
68
Views
1K
Thespeakerdude8
Thespeakerdude8
Back
Top Bottom