Yamaha CR-840 - protection relay not engaging

[lqpete11]

Hello,

New to me Yamaha CR-840.

I know this issue has been discussed, but I wanted to post my voltages and see if I have a bad IC 704 powerpack or if I should be looking elsewhere. The unit powers on, but the relay fails to engage.

I used the CR-640 schematic since it showed expected voltages.

Test Points
TL 0.2 VDC
TR 34.7 VDC

IC 703 (all VDC)
10. 3.52
9. 34.7
8. 0.236
7. 2.06
6. 0.835
5. -0.402
4 -1.57
3. -0.188
2. -34.8
1. -2.92

IC 704 (all VDC)
10. -8.08 (variable)
9. 34.6
8. 34.7
7. -8.05 (variable)
6. 34.5
5. -34.5
4. -23.6
3. 34.7
2. -34.7
1. -35.6

If it is the powerpack, any recommendations on a replacement? Should both be replaced at the same time?

Thank you,

Greg

 

[avionic]

IC 704 (all VDC)

8. 34.7

3. 34.7

IC704 looks bad..

 

[avionic]

If it is the powerpack, any recommendations on a replacement?

I have no clue..
# 1 reason I don't bother with chip amp models..

 

[chazix]

replacement

You can look for parts called STK0060II. All will be knock-offs, rather than original Sanyo parts (despite what might be claimed). If I were looking, I would check with Consolidated, who seem to be offering them currently:

STK0060II 10P SIP, Consolidated Electronics Inc

It is important to check that the emitter resistors are OK when a power pack has failed.

Another step that would be good to take, if you are up for it, is to check pre-driver function using the method in the thread with "ongoing saga" in the title. The thread is gnarly, but a good summary of the method was posted most recently by Nashou66.

 

[lqpete11]

You can look for parts called STK0060II. All will be knock-offs, rather than original Sanyo parts (despite what might be claimed). If I were looking, I would check with Consolidated, who seem to be offering them currently:

STK0060II 10P SIP, Consolidated Electronics Inc

It is important to check that the emitter resistors are OK when a power pack has failed.

Another step that would be good to take, if you are up for it, is to check pre-driver function using the method in the thread with "ongoing saga" in the title. The thread is gnarly, but a good summary of the method was posted most recently by Nashou66.

Thank you chazix,

I made it through the “ongoing saga” thread last evening and quickly tested the emitter resisters. Thank you for all the work you put in there. All emitter resisters test near 0.5k. The 390 ohm resistors between pin 11 on the pre’s and pin 3 on the power packs both tested at 385 ohms. I took this as potential good news for the health of the pre-drivers.

Pin 13 tested with high DC voltage (35.2) on the right pre-driver. Pin 14 was -3.5 & 15 was 40 VDC. The left pre-driver had 40 VDC on 15 and low VDC on 13 & 14.

My next question is do I need to remove both power packs to do the pre-driver test, or can I leave the good one in place and still listen via headphones with no speakers connected? I have 4 220 ohm resistors ready to go.

Thank you for the help,

Greg

 

[chazix]

leave the good one in place

This is fine.

 

[lqpete11]

This is fine.

The pre-driver test is done and, after an initial concern, shows the pre-drivers to be in working order. For some reason, the A output for phones had equal output on both channels regardless of the balance control position. The B output had equal volume and responded to balance and volume controls.

I ordered an STK 0060 II and think this should bring it back to life. Thanks again for all your help, both here and on the “ongoing saga” thread. As a side note, both pre-drivers have clearly been removed and they both have heat sinks added.

Greg

 

[chazix]

A output for phones had equal output on both channels regardless of the balance control position

That feels like the headphones were not getting a good ground connection, though that would be expected to also result in a sound that might be called hollow or tinny. The A and B 'phone jacks are both derived in the same way from the main L and R outputs.

 

[lqpete11]

That feels like the headphones were not getting a good ground connection, though that would be expected to also result in a sound that might be called hollow or tinny. The A and B 'phone jacks are both derived in the same way from the main L and R outputs.

I’ll check the A output‘s ground and also clean the jack. I looked at the wiring and saw they were fed from the same source, so I knew the pre-drovers were okay when I had good output on B.

Thanks again,

Greg

 

[lqpete11]

That feels like the headphones were not getting a good ground connection, though that would be expected to also result in a sound that might be called hollow or tinny. The A and B 'phone jacks are both derived in the same way from the main L and R outputs.

Just closing the loop. I got lucky and the first ST0060 II I ordered tested good. I just installed it and the CR-840 is playing happily as I type this. Bias on both channels was set at just under 5 mV.

Thanks again for all the help,

Greg