Eden WT-600 Power Problem

[kdawg]

Hello - I'm trying to troubleshoot an Eden WT-600... the two channels were accidentally plugged into the same speaker cabinet and it blew two power transistors plus the driver on one channel. I have the parts and I think this will be straightforward hopefully.

The second problem is that now when a tube is put in, all the lights turn off and there is not enough voltage for the heater. I have the schematics but there is nothing shown the power supply board. I tried replacing the TIP42C part of the heater circuit, no difference. I can see the voltage drop to about half when I plug a tube in... I did try different tubes also. I have a suspicion that one of the caps is not working but I don't know which ones are part of the filament circuit - can anyone help? Thanks

-kdawg

[Jazz P Bass]

Eden 600 schematic

Here is the Eden 600 schematic.
You will have to verify if it is the correct one.
I don't see why the pilot light would dim.
It looks like there are diodes on the heater circuit. 2 are zeners.
Might want to check them.

[Enzo]

On the schematic are some zener diodes next to the heater and transistor. Look for one of those to be bad. Also on page 14 of the file Jazz posted, the power supply is shown as a box, with a resistor in series at the "filament" output. Perhaps check the health of that resistor. if it has gone way high, then voltage woulod be there without a tube, but collapse when the load was put on.

[kdawg]

I tried changing the heater 15v zener (because I had one) as well as the 1N4003 on the power supply board, and the 470uF/25v cap to the fan circuit... no change. I still get -12V to the heater pin with no tube, then it drops to -4V with a tube in.

I checked all these with meter/diode test and they read OK:
R80 - 1K
D11 - 15v Zener (replaced)
D12 - 1N4003
D13 - 12v Zener
C35 - 1000uf / 25V (replaced)

All the values for the big 100 ohm and 47 ohm resistors check OK, should I still try replacing them? I only have a 150 ohm 10W.

Two of the thermal switches (US-602S) read open, two read shorts... aren't they all supposed to read the same?

I wish I had the full schematic for the power supply, just so I could visually see it. Traces are hard to see on that board.

Thanks
-kdawg

[Enzo]

Thermal switches do various jobs. SOme are normally closed and oopen when they get hot - those would be used to cut power to the circuit when it overheats. Others might be normally open and close when they get hot. Those could be used to turn the fan on to higher speed or to turn on a warning light for example. Look at the numbers on each one - if they are different, then the parts are different.

On the posted schematic it is C31, not C35. I don;t know what numbers are on your board, so I am using the part numbers off the posted drawing. Looking at the schematic, then measure the voltage across the heater supply - C31. Does that also drop when the tube is inserted, or does it remain up to voltage? We want to determine if the whole filament supply is collapsing or only at the heater itself.

[kdawg]

Sorry, yes I meant C31. That voltage to the base of TIP32 is also dropping when the tube is put in.

-kdawg

[Enzo]

Well that is consistent, but still how about the supply itself on C31?

YOu are getting the 12v without the tube, where are you measuring, at the socket?

Measure at the tab of the TIP - what happens there.

Possible scenario:

For example, if the voltage at C31 drops, then the whole supply is not getting enough current. But if that holds up while the voltage at the tube drops, then our little transistor circuit is not right.

If the collector of the transistor is not being supplied with the C31 voltage, then the tube heater will try to draw current through the base of the TIP, and likely will not be able to. SO even a good transistor won;t work if its collector has no good connection to the supply voltage.

[kdawg]

Here's some measurements:

Tube out
----
Collector: -22v
Base: -12.74v
Emitter: -12v

Tube in
---
Collector: -3.5v
Base: -2.7v
Emiiter: -2v

So the whole thing is dropping the supply voltage it appears? The only things I see between the transformer and the collector are a 1N4003 and the 100 ohm / 10 W. I'll try changing the resistor, I already had replaced the 1N4003 there.

[Enzo]

Before you change the resistor, what does the voltage do on the other end of it? I mean if the power end drops to 3v also, it can hardly be the fault of that resistor. And power off, measure the resistor - 100 ohms? Of course if the voltage stays up on hte power end but drops on the TIP collector end, then the resistor is supect.

The key to solving this puzzle is systematic troubleshooting to find where the problem lies. Changing parts to hope to find the bad one is not efficient.

I have no idea what is on the power supply board. If it is nothing more than a diode and the transformer winding, then power off, and measure resistance of the power transformer winding. An open winding will still read voltage, but can provide no current.

[kdawg]

I check the TX, it has about 36VAC with or without the tube in there and it measures in the low ohms. It's being half-rectified by a 1N4003, then it goes to the 100 ohm 10W - there is some other circuitry for another voltage supply to something else but hard to follow traces. The voltage at that 1N4003 / resistor junction goes from -28V with tube out to -14V with tube in.

Do you have a copy of the WT-400 schematic "standard" that doesn't have the right side cut off? I can see part of the power supply circuit on that one but it's cut off. I tried even just hooking up heater pins only on tube and no other pins, same issue.

-kdawgt

[Enzo]

I don;t have any Eden schematics at all.

[Jazz P Bass]

Filament Circuit

Can you verify that your board agrees with the schematic that we are all working with .
There are seven components.(minus the 100 ohm/10W R & rectifier diode).
Make sure the polarities of the diodes & capacitors is correct. (backwards)
We are dealing with a negative voltage.
Remove the 12AX7 & measure the resistance from the TIP transistor emitter to ground. It should be zero ohms.
Put the tube in & measure it again. Should be 20 ohms.

[Enzo]

I think he is concerned that the schematic you posted - and thanks for it - shows only a box for power supply.

[kdawg]

Yes the schematic you provided is right Jazz, but doesn't show the inside of the "power supply" box.

There is about 12 ohms with tube in, 1.5 M ohms with tube out.

-kdawg

[Jazz P Bass]

Eden 600

Can you hook up a 20 some ohm resistor from PNP transistor emitter to ground.
Test the emitter junction. If voltage is o/k something down stream is amiss.
Something is hogging current.
Did you recheck all of the polarities?
Nothing has been saig about C33.
Is the 12 volt zener good?