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C2x running hot (continuation)

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dsmart705

Well-Known Member
For anyone who has read through the "C2a vs C2x" post this is a continuation of it with an issue that was discussed in that thread. For anyone who hasn't it was discovered than my C2x runs at a much higher temp than the C2a. The temp seemed to be located on the left side which made the likely source the transformer. Anyways I decided to pull the C2x out of service to investigate and confirmed that the transformer is causing the extra heat. That in itself would be concerning but what is more troubling is that the transformer actually gets very hot when the unit it not switched on. These 2 pictures are taken roughly 25 minutes of the unit being plugged in but not switched on.

Back half of transformer
upload_2023-1-7_20-32-53.jpeg

Front half of transformer
upload_2023-1-7_20-33-18.jpeg

Ambient/chassis temp
upload_2023-1-7_20-34-56.jpeg

At this point I switched the unit on and the checked 15 minuted later. The temp in the center of the transformer was getting into "concerning territory"
upload_2023-1-7_20-36-44.jpeg

So I think it is fair to say that there is an issue with this unit and it will not be going back into service unitl it's sorted. After looking at the schematic it would appear as though there are 2 seperate transformers in one case. One is for phono and the other is for line, both of which are operated by the power switch although the line transformer is closed by the switch contacts and the phono is closed by relay contacts. I haven't tested anything but the problem would have to either be a failed/failing transformer, a failed/failing relay (has the typical relay "click" when turning on unit) or a failed/failing power switch for the transformer to be getting hot when not powered up. Even then im not sure why the transformer itself would be getting so hot under a low/no load condition.

Anyways if anyone might have some insight into this issue that would be much appreciated. There was a thread from many years ago with a similar issue but there was no resolution.

https://audiokarma.org/forums/index.php?threads/yammy-c2x-gets-hot.254899/
 
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Is yours a regular version? Check to see if the phono power supply stays on when the unit is turned off. In the C-2A vs. C-2X thread I did dive into this, and on the regular version I have on the bench the phono power supply was hardwired on all the time when it was plugged in. I disconnected the jumper wire and it now goes on/off with the relay. It's cold when off, and so far there are no issues with it powering on/off.
 
Asmodeus2112 said:
Is yours a regular version? Check to see if the phono power supply stays on when the unit is turned off. In the C-2A vs. C-2X thread I did dive into this, and on the regular version I have on the bench the phono power supply was hardwired on all the time when it was plugged in. I disconnected the jumper wire and it now goes on/off with the relay. It's cold when off, and so far there are no issues with it powering on/off.
Click to expand...

Mine is the Japan version. I have not done any troubleshooting yet but when the unit is plugged in and not switched on there is no power (+-20vdc) in either the line or phono sections. I do remember the wiring issues you discovered on your unit.....but this c2x does not have an additional jumper.

upload_2023-1-7_22-38-27.jpeg
 
dsmart705 said:
Anyways if anyone might have some insight into this issue that would be much appreciated. There was a thread from many years ago with a similar issue but there was no resolution.

https://audiokarma.org/forums/index.php?threads/yammy-c2x-gets-hot.254899/
Click to expand...

It turns out the C-2x mentioned in the cited link's first post is in fact a Regular (110-120V/220-240V) model in use in Australia. Units remaining warm/hot after power switch off is a known issue among C-2x Regular model owners. Those owners in the thread who cited their units as being cold/stone cold after switch off likely own other C-2x models.

Shade
 
I wonder if we could find the model number of the transformer and find a spec sheet so we can know what temps are normal.
 
Asmodeus2112 said:
I wonder if we could find the model number of the transformer and find a spec sheet so we can know what temps are normal.
Click to expand...

upload_2023-1-8_10-34-45.png

Here are the part numbers listed for the transformer. I'm not holding my breath for any specs on this particular transformer but my experience with SS audio gear from all manufacturers is that the power transformer does not get hot or even very warm during normal operation. This one get piping hot even with the power swtiched off which should be impossible as the phono primary winding is OL until the relay closes and the line secondary winding is OL until the power is switched on. As neither section has any rectified DC voltage present the issue points more to a failing transformer than either a failing relay or power switch. This of course would be the most unfortunate situation as a replacement transformer of this configuration/footprint might be very difficult.

I have not done any testing so my thoughts are all theoretical and I would love to prove myself wrong. Im by no means an expert here either as my training is mechanical and not electrical so my interpretation could also be lacking.
 
dsmart705 said:
View attachment 2761047

Here are the part numbers listed for the transformer. I'm not holding my breath for any specs on this particular transformer but my experience with SS audio gear from all manufacturers is that the power transformer does not get hot or even very warm during normal operation. This one get piping hot even with the power swtiched off which should be impossible as the phono primary winding is OL until the relay closes and the line secondary winding is OL until the power is switched on. As neither section has any rectified DC voltage present the issue points more to a failing transformer than either a failing relay or power switch. This of course would be the most unfortunate situation as a replacement transformer of this configuration/footprint might be very difficult.

I have not done any testing so my thoughts are all theoretical and I would love to prove myself wrong. Im by no means an expert here either as my training is mechanical and not electrical so my interpretation could also be lacking.
Click to expand...
Is there corrosion on or under the transformer? Can it be removed for inspection? Does it run hot with all its wires unsoldered from all boards it connects to? If so, then it might have developed an internal issue such as higher than normal resistance, etc. .
 
Sparkplug said:
Is there corrosion on or under the transformer? Can it be removed for inspection? Does it run hot with all its wires unsoldered from all boards it connects to? If so, then it might have developed an internal issue such as higher than normal resistance, etc. .
Click to expand...

No corrosion, transformer can be physically removed but the windings are all potted in the housing so not much to see there. My plan is to pull the relay and test, then pull the power switch and test to isolate the transformer. I have already pulled C436 which bridges the relay contacts for the phono transformer and it tests in spec.
 
dsmart705 said:
View attachment 2761047

Here are the part numbers listed for the transformer. I'm not holding my breath for any specs on this particular transformer but my experience with SS audio gear from all manufacturers is that the power transformer does not get hot or even very warm during normal operation. This one get piping hot even with the power swtiched off which should be impossible as the phono primary winding is OL until the relay closes and the line secondary winding is OL until the power is switched on. As neither section has any rectified DC voltage present the issue points more to a failing transformer than either a failing relay or power switch. This of course would be the most unfortunate situation as a replacement transformer of this configuration/footprint might be very difficult.

I have not done any testing so my thoughts are all theoretical and I would love to prove myself wrong. Im by no means an expert here either as my training is mechanical and not electrical so my interpretation could also be lacking.
Click to expand...

Just to be sure, you checked the regulator TR's for the phono section and they are off when the unit is off? TR's 129, 130?

The unit on my bench is not in a state that I can turn it on, but maybe by the end of the day. I will see what temp it runs at.
 
Testing the transformer in isolation would be my first step to eliminate the rest of the amp from consideration, or not. I’d also test the transformer output to make sure there’s no distortion. While at it, why not test the transformer input too, I’m sure you’re using another step-down transformer to get your hopefully clean 100V …
 
I started pulling parts this afternoon to isolate the transformer. At each step I checked to see if it would make a difference but nothing prevented the transformer from heating up. So far I have pulled the phono relay, power switch, line transformer rectifier diodes, phono transformer rectifier diodes and related capacitors connected to areas in question. As far as im concerned the primary and secondary windings of the phono transformer have been completely isolated and the secondary winding of the line transformer has been isolated. The only thing left in the circuit is the primary winding on the line transformer but without the power switch closing the secondary windings there shouldn't be much load there. I have attached a picture showing relavent voltages in red and things that have been removed in blue (everything tested with unit plugged in but not switched on)**no power switch!. I do not understand the voltages present on the line transformer secondary....there is nothing connected!! Anyways its getting late and i've been staring at schematics for far to long so I probably am missing something obvious here.
upload_2023-1-8_21-34-25.png
 
Well, on the phono the switch turns off the AC on the wall side, where as the line it turns it off on the device side of the transformer. So AC is going through it the windings on the line part. I'm not a EE, so I don't really know what that would do, but it is a difference.
 
Asmodeus2112 said:
Well, on the phono the switch turns off the AC on the wall side, where as the line it turns it off on the device side of the transformer. So AC is going through it the windings on the line part. I'm not a EE, so I don't really know what that would do, but it is a difference.
Click to expand...

Im not an EE either, that knowledge would sure be helpful in this situtation. Even with the voltage differences, with the line section secondary isolated there should be no load on the transformer at all. Basically im trying everything I can to not condemn the transformer but things are not looking good. All that heat coming from an idling transformer is a bad sign. It does make sense that the front half of the transformer (line windings) get hot quickly compared to the back half (phono) if the issue lies in the line section. I may have bought a fairly expensive paperweight :(
 
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dsmart705 said:
Im not an EE either, that knowledge would sure be helpful in this situtation. Even with the voltage differences, with the line section secondary isolated there should be no load on the transformer at all. Basically im trying everything I can to not condemn the transformer but things are not looking good. All that heat coming from an idling transformer is a bad sign. It does make sense that the front half of the transformer (line windings) get hot quickly compared to the back half (phono) if the issue lies in the line section internal windings. I may have bought a fairly expensive paperweight :(
Click to expand...
 
Have you measured the resistance of the secondary windings to see if there is high resistance in them. I would assume they would need to be disconnected from everything to get a clean reading.

Maybe also check the primary as well.

Athanasios
 
I don’t have the unit in front of me but wouldn’t it be easier to just disconnect/unsolder the transformer wires from the circuit boards than taking individual parts out? The center-tap (wire) of the phono transformer is chassis grounded in the schematic, is it still so? The voltages (7vac) seem low but I’d have to look at the circuit some more. From the schematic, voltages on Tr129 (cbe) are approximately 20V, 32.6V, and 33.2V respectively, with the emitter seeing the voltage right out of the bridge rectifier (33.2V). With the measured voltages of 8Vrms (11.3 Peak), I don’t see how you get up to 30 plus volts even with almost 10000uF filtering caps (two in parallel) hanging on the supply line that raise the peak rectifier output voltage by several volts. I’d expect a measurement of around 24Vrms out of the phono transformer secondary.

@Asmodeus2112 , hate to bother you but what voltages do you see on yours, if the unit can be turned on at the moment that is and if at all possible at the circled points below, if not then please ignore.
4CCFA11C-23DA-4CDD-8CF2-62436ED10CC7.jpeg

Thanks and please both be careful doing all this, it’s not free of danger.
 
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Nashou66 said:
Have you measured the resistance of the secondary windings to see if there is high resistance in them. I would assume they would need to be disconnected from everything to get a clean reading.

Maybe also check the primary as well.

Athanasios
Click to expand...
My thinking exactly.
 
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