And this is why I come here. In mono, I get output in headphones on both channels, but in stereo, only the right channel! So now to pull the drivers and test.
Yamaha CA-810 repair
- Thread starter bberkom
- Start date
petehall347
the brandy coffee man
stereo mono switch is before main amp . phones look to come from main amp . so if correct main amp is working . well apart from the heavy power consumption that is.
I pulled and checked drivers TR421 and TR423 and both test fine with my DMM and cricket.
Emitter R469 and R471 each give me a 0.6-0.7 ohm reading on my meter. Physically they don't appear damaged, but they must be open.
@petehall347 are you saying that there is a fault somewhere in the preamp section then? Or do we think it's the emitter resistors burned when the outputs went? I can hook it up to a separate power amp and test the preamp again while flipping the stereo/mono switch to see if both channels are there after I reinstall the driver transistors. Is it okay to leave the emitters out to test the preamp as long as the outputs are pulled as well?
Emitter R469 and R471 each give me a 0.6-0.7 ohm reading on my meter. Physically they don't appear damaged, but they must be open.
@petehall347 are you saying that there is a fault somewhere in the preamp section then? Or do we think it's the emitter resistors burned when the outputs went? I can hook it up to a separate power amp and test the preamp again while flipping the stereo/mono switch to see if both channels are there after I reinstall the driver transistors. Is it okay to leave the emitters out to test the preamp as long as the outputs are pulled as well?
In circuit or out of circuit? You meters test leads will add a little resistance to your reading when measuring less than 1Ω. Open would be a much higher resistance. I'm thinking your emitters resistors are good.
Short your test leads together. What resistance does your meter read?
petehall347
the brandy coffee man
put resistors back in
petehall347
the brandy coffee man
best see what happens with pre before looking at main .
I retested the preamp section with left channel outputs removed, and it sounds great in both channels in stereo mode. While I was at it, I tried headphones again, and I got good, clean sound out of both channels in stereo mode as well. I am guessing there was a dirty switch or contact when I tested earlier, or removing and reinserting the pre/main jumpers brought the channel back.
So my issue is still that the amp fails the DBT with the left output transistors installed. Driver transistors test fine as do emitter resistors. I inspected areas with the brown glue, and although a little dirty, no components were severely corroded. I also retested the new outputs to make sure they are good, and they test fine. Any ideas on what to look at next?
So my issue is still that the amp fails the DBT with the left output transistors installed. Driver transistors test fine as do emitter resistors. I inspected areas with the brown glue, and although a little dirty, no components were severely corroded. I also retested the new outputs to make sure they are good, and they test fine. Any ideas on what to look at next?
petehall347
the brandy coffee man
there are a few fuse resistors to check start with fr405 fr407 680 ohms
FR405 and FR407 test 687 and 689 ohm respectively in circuit. FR401 and FR 403 tested a little low, but I tested them in circuit and they were at least in the ballpark.
However, FR409, which should be 68 ohms, is testing open, or at least I think it is. I get no reading at the lower ranges of my meter, but when I switch my meter to 2M, 20M and 200M, the reading just keeps climbing until it's out of the meter's range, so I think this one is shot. Seems like it may be my problem.
I was planning to replace all of the fusible resistors anyways once I get it up a running. I have seen another CR-810 thread where 1/2 watt metal film or metal oxide were used in place of these. The 68ohm resistor was also bad in this thread.
However, FR409, which should be 68 ohms, is testing open, or at least I think it is. I get no reading at the lower ranges of my meter, but when I switch my meter to 2M, 20M and 200M, the reading just keeps climbing until it's out of the meter's range, so I think this one is shot. Seems like it may be my problem.
I was planning to replace all of the fusible resistors anyways once I get it up a running. I have seen another CR-810 thread where 1/2 watt metal film or metal oxide were used in place of these. The 68ohm resistor was also bad in this thread.
petehall347
the brandy coffee man
see if d417 survived
petehall347
the brandy coffee man
i would think to use the correct fuse resistors as they marked with current ratings .avionic will know better than me .
1/2 watt with flameproof coating either metal or carbon film.Or metal oxide.
This metal oxide fits the bill
https://www.mouser.com/ProductDetail/KOA-Speer/MOS1-2CT52R680J?qs=sGAEpiMZZMtlubZbdhIBICYVxaT5CDYBtshSe0il3HI=
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Also,
look and see if there's any lavender Matsushita capacitors in the amp. REPLACE ON SIGHT!. I've found more problems with them in gear than any other brands. One was causing an issue on my CA-810, which has since been sold. It was in the location you can see in this photo (look for the cap that looks new
).
entire restoration thread here.
look and see if there's any lavender Matsushita capacitors in the amp. REPLACE ON SIGHT!. I've found more problems with them in gear than any other brands. One was causing an issue on my CA-810, which has since been sold. It was in the location you can see in this photo (look for the cap that looks new
).
entire restoration thread here.
I finally had time to go through the amp and put a cap order together. A couple mistakes in the schematic, but easy enough to match to what was in the amp. I have the same purple cap in that location in my amp, @jheu02 and it will be replaced along with all of the other electrolytics once I can get it to pass the DBT. I'm ordering all new fusible resistors too, so I hope replacing the one that was bad takes care of the left channel short. I'll report back once I get that fusistor replaced and reinstall the left outputs.
Just replacing a fusible resistor will not clear the short. The resistor is just a fuse. There is a possibility of a shorted transistor, diode or capacitor causing the fusible to burn open.
Obviously, the issues could be completely different between why your amp and mine weren’t working. But here’s a quote from my write up about how to get mine working again.
“I did a little more looking around/troubleshooting and noticed a purple Matsushita cap that was a definite replacement sometime in this amp's past. The sleeve was pulled back around the top of the can. C603 IIRC, 220uF/10V. It also had what looked like smoke marks on it. So, I pulled and checked it with the capacitance function of my mulitmeter...open, no reading whatsoever. Got a Panasonic FM 220uF/25V from my stocks and soldered it in, then pulled all the OPTs again and put it on the DBT. Nice check and relay clicked in ~3 seconds. With that working I put the R channel outputs back in, checked the bias on the DBT and set it low, then reset on line power and checked to see if there was sound. Other than scratchy pots, I got nice sound.
So, tonight, I'll swap the good outputs into the L channel and repeat the process of checking setting bias on the DBT and then if all goes well, listen to the sound from that channel too. If the bulb doesn't dim properly, I'll know there's more troubleshooting to do on the left side before I get into serious restoration/recapping.
EDIT
I swapped the OPTs, bulb dimmed, checked bias...60ishmV...way too high. Dialed it back 0mV on the dim bulb and then went to line power. Brought the bias up to 19.7mV..close enough to 20 for this check. Lo and behold...
.”
Hope this helps...
“I did a little more looking around/troubleshooting and noticed a purple Matsushita cap that was a definite replacement sometime in this amp's past. The sleeve was pulled back around the top of the can. C603 IIRC, 220uF/10V. It also had what looked like smoke marks on it. So, I pulled and checked it with the capacitance function of my mulitmeter...open, no reading whatsoever. Got a Panasonic FM 220uF/25V from my stocks and soldered it in, then pulled all the OPTs again and put it on the DBT. Nice check and relay clicked in ~3 seconds. With that working I put the R channel outputs back in, checked the bias on the DBT and set it low, then reset on line power and checked to see if there was sound. Other than scratchy pots, I got nice sound.
So, tonight, I'll swap the good outputs into the L channel and repeat the process of checking setting bias on the DBT and then if all goes well, listen to the sound from that channel too. If the bulb doesn't dim properly, I'll know there's more troubleshooting to do on the left side before I get into serious restoration/recapping.
EDIT
I swapped the OPTs, bulb dimmed, checked bias...60ishmV...way too high. Dialed it back 0mV on the dim bulb and then went to line power. Brought the bias up to 19.7mV..close enough to 20 for this check. Lo and behold...
.”Hope this helps...
