Yamaha CA-1000 repair. My first Yammy!
- Thread starter smurfer77
- Start date
smurfer77
Super Member
Tell me about it! If it made sense, we wouldn't be here
. Uploading a pic at end of post to show the voltage - really, I'm not going crazy! I've pulled TR606 and it tests ok, but not ruling it out, but not sure it alone explains all of my weird voltages.Have already mentioned I have around -25V at all 3 pins of TR606. I know... bad. See pic below (I wrote "ok" just because I pulled and tested the transistor).
I was thinking switch in my original post. You know, when I flip the switch to class A (with power off, like a good little boy) the voltages are still not quite right, but they come back to sanity (for example, about -2V on base of TR606 .
Will check those carefully next.
Yes. See voltages on pic below.
Well hello! Fancy bumping into you. Thank you for the welcome. What crazy world have I entered into!Welcome the the wonderful world of Yamaha smurfer !!
nashou
Thank you everyone for all of the comments. Really, I'm not crazy. And you guys are keeping me from losing my temper.
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blhagstrom
Mad Scientist, fixer.
I had a CA-1000 with some really whacked voltages and the A/B microswitchs were bad.
The OP says high voltage on the drivers, all pins but the base of the outputs are 0!?!?!
Double check those outputs. I'm thinking the outputs are shorted and back feeding voltage to the drivers.
smurfer77
Super Member
Output transistors were checked. Also same result when they are not installed. But maybe i should check the PCB near there as skmeone had made a mess of the TO3 socket installation previously. Also will check that bias switch.
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blhagstrom
Mad Scientist, fixer.
If someone has been hacking, check everything they touched.
Are the drivers original? Are they in right?
Hack jobs can be real confusing. You can't assume anything is "normal".
I've wasted more time chasing my tail because someone screwed up a repair because they should not have been in there.
Are the drivers original? Are they in right?
Hack jobs can be real confusing. You can't assume anything is "normal".
I've wasted more time chasing my tail because someone screwed up a repair because they should not have been in there.
Measurements from a unit on the bench with new switches and power amps refurbished however
still being rebuilt so measurements with el cheapo mm might be misleading
L&R channels shown
NORMAL...BC...6 ohms 2ohms
BS...475 ohms 461 ohms
CS...468 ohms 460 ohms
CLASS A..BC...4.28k 4.1k
BS...4.28k 4.1k
CS...15 ohms 5ohms
still being rebuilt so measurements with el cheapo mm might be misleading
L&R channels shown
NORMAL...BC...6 ohms 2ohms
BS...475 ohms 461 ohms
CS...468 ohms 460 ohms
CLASS A..BC...4.28k 4.1k
BS...4.28k 4.1k
CS...15 ohms 5ohms
smurfer77
Super Member
They appear to be original. Haven't pulled them to test them, but resistances across it and to nearby components look good (but not ruling them out).
I have 73V (Normal) and 32V (Class A)
I have:
Mode------Pins--------L------------R-------
NORMAL...BC.....0.4 ohms.....0.4 ohms
..................BS.....469 ohms....472 ohms
..................CS.....469 ohms....471 ohms
..................AB....1.52k ohms...2.38k ohms
..................AC....1.52k ohms...2.38k ohms
..................AS....1.99k ohms...2.85k ohms
Class A.....BC.....1.52k ohms...2.38k ohms
..................BS.....1.52k ohms...2.38k ohms
..................CS.....0.3 ohms......0.2 ohms
..................AB....1.52k ohms....2.38k ohms
..................AC....0.3 ohms.......0.3k ohms
..................AS....0.3 ohms.......0.3 ohms
So we have some difference between Left (bad) and right (assumed good) but we do have VR604 messing with all AX numbers and VR603 varying anything involved pin B so not jumping to conclusions for now. I guess I could disconnect them from the main amp board and measure again...and might as well inspect and clean that switches while I have the lid off.
Agreed. B-C short for NORMAL mode. Looks like A-C-S are shorted in my measurements for CLASS A mode and that is what I see in the schematic too.
Yes my numbers on the main amp schematic were all in Normal mode. We see pin B and C at about the same voltage give or take 1/4V, which has to be the case as you noted BC are short. So I'm going to clean that switch I guess, but I guess the issue is coming in on the main amp board... I may have to chase the source of that -ve DC after all. Further suggestions? (otherwise I'm just going to start checking all traces and pulling all transistors after TR604 to check... probably starting from drivers and working back. I've already checked all relevant caps and resistors on the board.)
Thanks again for the suggestions!
Your tracing of the negative voltages may yield the results.
TR610(base) is just totally wrong. Possible source TR612?
Measure voltage at OUT pin and TP3 and 4 on problematic side, just to help with source.
TR610(base) is just totally wrong. Possible source TR612?
Measure voltage at OUT pin and TP3 and 4 on problematic side, just to help with source.
We've come full circle.
Attachments
Hi Smurfer,
Am off shift now so had a bit of a chance to peruse.
First impressions around TR606 is forget the Normal/Class A switching as this looks to be bias shifting on the base or a Collector resistor shorted to add current. The first port of call for me would be to find out where the +ve Collector supply has gone as you have -25V on all pins. No matter what the switch is set to there should be a +ve voltage coming via the resistors from TP1. The frippery around the Base and Emitter can only function if the collector has the +ve voltage to pull everything upwards. See where that gets you. I would say R614 has gone High or O/C. If not it should be cooking nicely.
GPS16
Am off shift now so had a bit of a chance to peruse.
First impressions around TR606 is forget the Normal/Class A switching as this looks to be bias shifting on the base or a Collector resistor shorted to add current. The first port of call for me would be to find out where the +ve Collector supply has gone as you have -25V on all pins. No matter what the switch is set to there should be a +ve voltage coming via the resistors from TP1. The frippery around the Base and Emitter can only function if the collector has the +ve voltage to pull everything upwards. See where that gets you. I would say R614 has gone High or O/C. If not it should be cooking nicely.
GPS16
Hi Smurfer,
revised conclusion. Looked at the drawing from the thread and not the one from the manual. From the voltages you have added in red and that you have also said TR606 is functional, there is 2 volts across the Base/Emitter of TR606. This would turn the transistor hard on. Also from the voltages on the 2 collector supply resistors there appears to be 8mA going somewhere!!! The stages afterwards seem to be isolated by reverse diodes so it looks like the current is in fact going down TR606. It looks like "mbz" is on the right track. What does R617 measure at?
GPS16
revised conclusion. Looked at the drawing from the thread and not the one from the manual. From the voltages you have added in red and that you have also said TR606 is functional, there is 2 volts across the Base/Emitter of TR606. This would turn the transistor hard on. Also from the voltages on the 2 collector supply resistors there appears to be 8mA going somewhere!!! The stages afterwards seem to be isolated by reverse diodes so it looks like the current is in fact going down TR606. It looks like "mbz" is on the right track. What does R617 measure at?
GPS16
smurfer77
Super Member
GPS! Welcome aboard on another adventure (GPS has helped me out on several projects at this stage, after we 'met' via a reel-to-reel rebuild thread I was doing) - you are most welcome!!!
R617 is also okay. Just measured it now as well.
Am still suspicious of the driver area but you guys know more about these circuits then me for sure so let's see where this takes us. Would it be interesting if I take voltages around TR606 with the transistor removed? Sadly, I have to go to sleep now otherwise I would press on with some measurements... might be busy next couple of days with regular work too.
It is a nice looking machine though... might not look bad with it's silver face next to the RT-707 one day.
R614 is sitting at 5.6kOhm where it should be... and up, it really has 50V across it.
R617 is also okay. Just measured it now as well.
Am still suspicious of the driver area but you guys know more about these circuits then me for sure so let's see where this takes us. Would it be interesting if I take voltages around TR606 with the transistor removed? Sadly, I have to go to sleep now otherwise I would press on with some measurements... might be busy next couple of days with regular work too.
It is a nice looking machine though... might not look bad with it's silver face next to the RT-707 one day.
smurfer77
Super Member
This morning, just before running to the train station I had 10 minutes spare and decided to pull TR606 again. The part tester shows hFE = 214 and Vf = 0.72V. While TR606 was out I did power up the amp (output transistors are out at the moment too) and the voltages on the pins were -20, -25 and -28 V (sorry, I didn't take note which was which right now... have to run).
TR606 has caused me issues in the past but I have to let it go in this case, high surronding voltages
point elsewhere.
Keep an eye on TR626, I've seen a few of these toasted. It won't be the cause of this problem.
From your measurements the OUT pin is at about +0.2V.
Will wait on your measurements especially around TR610,612.
