Sparkplug
Super Member
Which is it, Tr705, 706 or Tr713, 715? Emitter or collector?
-
Please note that there are a few updates and clarifications made in the Audiokarma Rules, mostly relating to advertising and the addition of the new "Paying it Forward" & "Giving back" forums in the AudioKarma Audio Marketplace section.
Yamaha CR-600 restoration advice
- Thread starter Joolian
- Start date
You could pull C723 and measure it's resistance. It should quickly reach a high resistance (MΩ) as the MM charges it up. If it stays at a low resistance it has shorted and is creating a path to ground.
Edit: Since this is a electrolytic polarized capacitor connect the leads the right way round (it is good practice to discharge capacitors before testing)
Edit: Since this is a electrolytic polarized capacitor connect the leads the right way round (it is good practice to discharge capacitors before testing)
Last edited:
I tested TR705 as I was just checking components along the trace that the outside end of FR701 sits on to see if any of them were causing that trace to have low ground resistance. TR713 and TR715 are the output transistors that are having low ground resistance on their collectors
I will check C723 and C725 tomorrow!
Sparkplug
Super Member
Not sure what you’re seeing is abnormal. The ±BL/R supply lines go straight to the power supply through F801~804. With those fuses removed, repeat your measurement, any change. Double check the 4700 μF 35V filter caps for integrity.
It's actually C723, my schematic is not real good, failing eyesight...
It's the obvious path from TR705e to GND
Is it reasonably easy to get a pix of the trackwork in this area/left channel power amp.
13ohms from TR705e does not align with any paths in the schematic so looking for a solder bridge or ...
50V abouts over 13k is only 4mA, hardly a short, I need to review past posts.
I take the point that the other channel shows OL
edit thread summary
Left channel emitters showing +37.5V
Recapped
6V offset both L&R, power supply issue, resolved
5k from left output collectors to GND, fuses blow, about 10mA
So still an issue with left channel power amp. Bit of misinformation on possible low resistance paths.
Plz dbt power up (75W-100W) then measure dc voltages at TP1,2,3,4 all to GND
Also measure at TR713 then TR715 collectors/cases
Last edited:
petehall347
the brandy coffee man
is this damaged ?
Bias VR adj possibly going open???
No, it has continuity in all three directions coming off it
Okay, desoldering one end of the jumper J701 fixes the short for TR713, but not for TR715. I’m thinking it has to be something in the D701/D702 area. I pulled C703 and C704 to test resistance between the terminals, but they just read 0L the whole time (having both removed also doesn’t change anything so presumably they’re okay?). I feel like I’m right on top of it
J701 is the jumper coming off the collector of TR713 and going towards the middle of the board. Emitter of TR705 is still 13k ohms but I don't know if that's anything to be concerned about. I tested resistance between the two legs of each capacitor.
I said pulling the jumper fixed the short for TR713, but upon checking again it's maxing out around 90k ohms on both sides of FR701. Definitely a big improvement but not perfect.
Attachments
Connects -BL and one side of FR701 to R713
If you measure the resistance of a capacitor and it measures OL right from the beginning it is open. It sounds like you are saying C703 and C704 are open? Did you discharge them first?
Edit: Nevermind. These are 0.1μF caps so it would instantly hit OL. I thought we were talking about higher value electrolytics.
Edit: Nevermind. These are 0.1μF caps so it would instantly hit OL. I thought we were talking about higher value electrolytics.
Last edited: