Eden CXC-400 Cooling Fan Does Not Come On

[Johnrcurry]

I am working on an Eden CXC-400 bass amp. According to the manual, the fan is supposed to be continuously on, but it does not come on. The fan plugs in to a header on one of the circuit boards (see attached picture). The fan is a 12vdc fan and it works when I hook it up to an external power supply. There is no voltage (actually 0.28vdc) at the header pins. Does anyone have a schematic for this amp to help me figure out where the 12 volts are supposed to come from? Or does anyone have experience with this amp/problem or a theory what may be going on?

Thanks for any help you can give.

John

[Enzo]

Eden is now part of Marshall. Try contacting Marshall and see if they will send it. At worst they say no.

[Jazz P Bass]

Take the amp out & trace out the fan circuit.
The board is marked 'Fan + -'.
Use your meter & see if the - is connected to ground or not.
Usually one or the other is attached to it's respective pole & the other is governed.
It most probably has a thermal input from the heatsink.
If it does, that would be to speed up the fan when the heatsink is hot.
So then you need a speed circuit . Probably one transistor (& associated resistors/capacitors).
At least the board isn't that crappy blue (hard to see the traces)

[Johnrcurry]

Thanks for your responses. I've sent an email to the customer service people at Eden/Marshall asking if they can send me the schematice. On further studying the board, as suggested by Jazz P Bass, the " - " pin on the fan header is not grounded. When I ground that pin with the fan plugged in and the amp turned on, the fan runs. Also, the plug next to the fan header has two white wires that lead to a device attached to the heatsink, probably a thermal sensor as you suggest. That suggests to me that the fan is thermally controlled. Is there a way for me to test that circuit, other than just playing the amp and seeing if the fan comes on? Also, is there a way to know whether the fan's not coming on because the heatsink is not hot enough, as opposed the circuit being faulty? So far, in playing the amp the fan has not come on, but then again, the heat sink has not gotten particulally hot (i.e. it's not so warm I can't put and keep my hand on it).

Thanks.

[Jazz P Bass]

So where does the - pin go to?
If you ground it, the fan operates.
So it has to go to a transistor or something like it.
I have seen little LM something or other ic's that are a thermal voltage control.
I would not assume that the thermal sensor is for the fan.
Unless you can verify that it is involved in the - leg of the circuit.
It may be involved in the 'thermal shutdown' circuit.
Are there any more sensors on the heatsink, other than that one.

[Johnrcurry]

Thanks for your response. I'll try to explain what I've found using the attached pictures. Just for background, here's an overall view of the amp:



Pin 1 of the fan header goes to the " - " leg of the capacitor right next to it:



The white connector next to the fan header is the one that leads to the device attached to the heat sink. This connector is labeled "STAT" on the circuit board:



The wires from the white connector connect directly to the device attached to the head sink. You can see it here, below the circuit board and directly underneath the transistor (2SA1494):



Here is a close up view of the device itself:



As far as I can tell, those wires do not connect to any sort of transistor. The " - " pin of the fan header seems also to be connected to the pin nearest it on the white "STAT" header. I say that because I measure 0 ohms resistance between the two.

There is a second device attached to the heat sink like the first. It is located under the circuit board direclty underneath the other transistor. The wires from that device lead to the bottom of the circuit board to which the transistors are attached, which does have a number of transistors.



Hopefully this sheds some additional light on the matter. Thanks again for your help.

[Jazz P Bass]

My suggestion of tracing out the fan circuit still stands.
Unless someone is very familiar with this amp, the pictures do not help.
What is required is a schematic drawing.
You have the amp.
I would start with a layout drawing.
Draw the components around the fan header.
Start with the header & follow where the PCB traces go. Draw that.
It really is not that difficult on a board like this.
Whether or not the heatsink sensors are involved in the fan circuit will be revealed when you trace it out.

[Enzo]

Your device is a thermal switch. I imagine there is no continuity between its two terminals. When the heat sink gets up to the temperature the thermal is rated for, it will close its contacts and complete the fan circuit.

Plug the fan back in and play a heat gun on that thermal sensor and see if the fan clicks on.

If my thinking is correct, that would be a "normally open" thermal sensor or "thermostat." You also see them commonly as normally closed. IN those cases they are in series with the mains. If the heat sink gets too hot, it breaks the circuit, removing mains power from the amp until it cools. Plenty of amps use both types.

[Johnrcurry]

Jazz P Bass and Enzo, thanks for your input.

Enzo, you are right. There is no continuity between the two terminals of the thermal switch, or the two pins on the "STAT" header. When I jumper the two pins on the "STAT" header the fan comes on. I tried applying heat to the heat sink (using a hair dryer). The heat sink got hot enough that it was uncomfortable to keep my hand on it, but the fan had not come on. I'm hesitant to apply too much heat, but at the same time, I'm not sure I gotten it hot enough to accurately conclude that the switch is faulty. Any insight on how far I can go with heating up the heat sink?

Thanks

John

[Enzo]

A heat gun is like a grown up hair dryer. It gets a LOT hotter, but also confines the air blast a lot more.COnsider this, we want to test the part, but it is on a heat sink. The heat sink exists for the sole purpose of conducting heat away. SO dismount the thermostat and hang it in the breeze. Now your hair dryer can heat it without fighting the heatsink. Measure resistance across the terminals. DOn;t do this with the unit powered. You could do it with the unit powered, but then you are just ASKING for something to slip or come loose and fall into the amp works and BVVZZZFFFTTT!!

And if nothing else, with the sensor loose, hold a soldering iron against its bottom for a moment.

There probably are part numbers on it, we could look up the part and find its temperature rating. I think Spemco is a common brand, though I might be remembering that wrong.

[Enzo]

A heat gun is like a grown up hair dryer. It gets a LOT hotter, but also confines the air blast a lot more.COnsider this, we want to test the part, but it is on a heat sink. The heat sink exists for the sole purpose of conducting heat away. SO dismount the thermostat and hang it in the breeze. Now your hair dryer can heat it without fighting the heatsink. Measure resistance across the terminals. DOn;t do this with the unit powered. You could do it with the unit powered, but then you are just ASKING for something to slip or come loose and fall into the amp works and BVVZZZFFFTTT!!

And if nothing else, with the sensor loose, hold a soldering iron against its bottom for a moment.

There probably are part numbers on it, we could look up the part and find its temperature rating. I think Spemco is a common brand, though I might be remembering that wrong.

[g1]

You really need to find out whether the manual is correct or not. You are chasing this problem because of something the owners manual said (that the fan is continuously on). You need to get in touch with Eden, or find a schematic or someone who has the same model amp. That would help you find out if this amp is normal or has a problem. Is there a complaint of the amp shutting down due to overheating? I would think that would be the case if the fan is never coming on.

There are a few possible scenario's ...
1) All is well, the owners manual is wrong. In this case the fan is one speed and only comes on when the temp. switch on the heatsink gets hot enough, you haven't got it that hot yet. As Enzo mentioned, try removing it from the heatsink and heating it up with an ohmmeter connected. It should go low resistance when it gets hot enough to close the switch.
2) The fan is 2 speed and the low speed mode is not functioning. In this case there may be a resistor or something that runs the fan at reduced voltage when the thermal switch is open. That resistor or circuitry could be faulty. The thermal switch still may also be faulty and needs to be checked as above.

[MarkusBass]

I think that g-one is right (in both cases). You can clearly see a thermal switch, which is on only when the heatsink temperature is above a certain threshold. You can just short it with a screwdriver to see whether it has problems. In this amp there is 1 or 2 resistors which are in series with the fan. One of them is 10W but still it fails quite often. I can even see the resistor on your photos (e.g. #2 - the holes below the capacitors - can you see something white below?). The resistor should be attached to the enclosure but after sevral years of usage it is not any more. Just remove the power supply board and see what's below it. If this is it, make sure that the new resistor is properly cooled.

Mark

[Johnrcurry]

Enzo, g-one, and MarkusBass thanks for your help. g-one, you're right. The amp has not been acting up. The only reason I began looking into this is because of the note in the owner's manual saying that the fan is continuously on. Once it became clear that the fan is controlled by a thermal switch, I just wanted to confirm that the circuit is working as it should. With Enzo's advice, I've been able to do that. As Enzo suggested, I removed the thermal switch, connect an ohmmeter and applied heat direclty to the device. The switch closes (as it should) when heated, and opens again when it cools off. I also checked the resistor, as MarkusBass suggested, and it is fine, too. At this point, I think I've verfied that all parts in the circuit are working, and it's safe to conclude that the reason the fan hasn't come on when I've used the amp is that it hasn't been hot enough.

I appreciate everyone's help.

John