• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

Yamaha CR-820 - guidance and possible help needed

Hi!
Yes, it is indeed a bit dodgy. I share your idea. More sites should turn up when doing a google search.

Would appriciate if somwone more knowledgable could comment on this transistor. It is a long wait for the onisem at Mouser. It is over a uears wait for that transistor, unless you can find at other vendor.
 
I went ahead and bought that lot of 2000 at Amazon. I sure hope I don't regret it! I'll try selling lots of 100 on ebay and see how that goes. I think 100 is a reasonable number for us repair technicians. And these are very useful transistors. So, if any of you are interested, let me know.
 
Hi!
It has been a while since I posted. Finally got some time to work on the unit. Replaced the damanged parts. as follows.

Replced the 68 ohm 85 ma with a 68 ohm resistor
Replaced the two 1.5k resostors (lifted from the pcb)
Replaced the 2 fuse resistors with 4.75k resistors (lifted from the pcb)
Replaced A218 with a new MJE15033
Replaced the two 0.22 ohm 1 w rsistors
Replaced all four 0.47 ohm resistors.
Replaced the two transistors leaned towards te heat sink with two matched 2240GR with slightly lower hfe (665mV) Curved side towards heat sink with paste added
Replaced all four end transistors according the attached picture. New mica and new paste.

Sadly when firing the unit up, the DBT lights up like a Christmas tree. I have revisited solder joints, resoldered when I saw fit to do so. I have also cleaned the pcb from old and new flux with alcohol. When I power it up for a couple of seconds only and measure rail voltage from the +30V pin, I get a very low reading, only a few volts. So something is succing a lot of juice. All components have been replaced with care, but the once under the curved chassi at the top of the pcb was a challenge to fit. It is however highly posible that I messed things up, but I can't really see where, as most of the components are pretty stright forwad to replace. But I also know that being an old newbe, things can go south quick. I hope that it can still be fixed.

Any help is welcomed and much appriciated, as I'm lost without this goups expertese. I now hope for the best! Tnx!

https://www.dropbox.com/s/dc4xjn54ig0107o/IMG_20220508_181051.jpg?dl=0
https://www.dropbox.com/s/quit18xfg18fmvb/IMG_20220508_181107.jpg?dl=0

IMG_20220508_181051.jpg

IMG_20220508_181107.jpg
 
Last edited:
Measure the DC voltage at the output transistor metal cases . 94 G will be a negative voltage . 93 G will be a positive voltage. Each should be in the 44vdc ballpark. A little less with the dim bulb.
 
avionic said:
Don't know..

You haven't identified them yet !
Click to expand...
Hi!
These two resistors replace the resistors that had the white fire proof fabric wrapped around them. The ones I got are 4.75 ohm @ 1 watt. Should they have been 1/2 watt instead? They are fuse resistors if I remember correct.

Don't know if this answers your question.
 
avionic said:
Measure the DC voltage at the output transistor metal cases . 94 G will be a negative voltage . 93 G will be a positive voltage. Each should be in the 44vdc ballpark. A little less with the dim bulb.
Click to expand...

I will attend to this tommorow as well. Report back when it has been done.
 
Getting back to the JCC transistor dilemma. I just came across another thread elsewhere on this forum called something like "10 worst transistors". These very JCC transistors are mentioned there. He actually contacted Onsemi asking about this JCC marking. These are indeed genuine Onsemi transistors!! Seems they have changed their labeling. By the way, the 2000 that I ordered got cancelled, however, Mouser does stock the 2sc1815.
 
johnhoef said:
Getting back to the JCC transistor dilemma. I just came across another thread elsewhere on this forum called something like "10 worst transistors". These very JCC transistors are mentioned there. He actually contacted Onsemi asking about this JCC marking. These are indeed genuine Onsemi transistors!! Seems they have changed their labeling. By the way, the 2000 that I ordered got cancelled, however, Mouser does stock the 2sc1815.
Click to expand...
That's good to know., thanks for posting!
 
avionic said:
Measure the DC voltage at the output transistor metal cases . 94 G will be a negative voltage . 93 G will be a positive voltage. Each should be in the 44vdc ballpark. A little less with the dim bulb.
Click to expand...
Hi!

I get these voltage readings when measuring over the casing and ground. From back to front of unit:

2.8V
-2.7V
2.7V
-2.7V
 
JorgenSWE said:
I will attend to this tommorow. Report back when it has been done.
Click to expand...
Hi!
I assume it is the three resistors sitting in between the transformer to the four caps. One with white tubing.

When mesuring in the compment tester I get a transistor reading. When measuring with the MTM i get a M ohm or infinite reading, I think that they are smoked, big time. All are measured out of circuit.

What should they be replaced with?
 
JorgenSWE said:
Hi!

I get these voltage readings when measuring over the casing and ground. From back to front of unit:

2.8V
-2.7V
2.7V
-2.7V
Click to expand...
Have you replaced the two large caps ? Need to check D812 and D813 out of circuit...

Your unregulated power supply is not working. Either totally shorted out. Or not even connected.. 2.7 volts isn't going to cut it.

Do you get any sign that power is even applied to the unit ? Like the power on LED ?
 
Last edited:
JorgenSWE said:
Hi!

I assume it is the three resistors sitting in between the transformer to the four caps. One with white tubing.

When mesuring in the compment tester I get a transistor reading. When measuring with the MTM i get a M ohm or infinite reading, I think that they are smoked, big time. All are measured out of circuit.

What should they be replaced with?
Click to expand...
Post a photo of what your measuring with a component tester..
JorgenSWE said:
I assume
Click to expand...
Don't assume anything....
 
Hi!

Yes, all the caps have been swapped on this board. I also swapped the power cord.

When powering up, the power led does not light up. When I firtst got the unit it did a little bit. I also saw that the other diods for AM/FM lit up some, but not now. I also measured all the fuses, they measure ok with an ohm meter set on continuity.

I desoldered the two diod bridges as you asked me, as seen in the picture below. When I measure with my analog meter one lead on the bridge, the other on the pin, one at s time, I get continuity on both diods, in one direction, but not the other. Measuring the other bridge I have to swap the leads and then I get continuity on both diods. Seems ok to me if this funtions as the rectifier bridge.

I tried using my component tester, but I got a reading telling me it was a transistor?!? It was the same for both, so I took my analog multimeter instead, using the ohm function. Measuring as you would measure a regular diod. Don't know if that would tell you anything specific. Just thought I should mention it.

I also desoldered the FR as seen in the picture. It measures 17.8 ohms. Seems out of spec.

When I first started the repair, I tested the rail voltage on the pins. They all measured ok. Now, not so much.

Again, thank you for your time and willingness to help.
 

Attachments

  • 16522092134095275477831390503839.jpg
    16522092134095275477831390503839.jpg
    29.6 KB · Views: 18
You must log in or register to reply here.
Back
Top Bottom