Need Help: Orange CR20dlx - No Power

[thehallofshields]

Amp died on me while I was in the bathroom. No LED Power, no Sound.

Outlet - Check
Cable - Check
Fuse - Check
I/O Switch - Check
Wires - Check
Connectors - Check

Diodes Near Rectifier - Check

What should I check next?

[Roly]

Please find and post the circuit.  Until then we are flying blind.


Remove the mains lead from the power input socket on the rear and using your multimeter on the ohms range check the resistance between the two mains connections (either side).  With the mains switch off it should be infinite, with the mains switch on it should be in the order of tens to hundreds of ohms.

If you can't get a lowish resistance with the power switch on then you have an open circuit somewhere in the mains input.  Check the fuse with your ohmmeter, these can sometimes give up and still look intact.

If you can get some continuity on the mains side the next thing to check is that you have some low AC volts going to the rectifier diodes from the transformer.  If you do then check that you have some DC voltage on the output of the rectifier/first filter electrolytic cap.

[JHow]

According to orange web site they only supply schematics to "authorised   repair centres" or dealers.

Assuming you didn't mean that you took the amp with you to the bathroom, how did you leave it (running?) and fir how long?  Did it get knocked over or anything like that? Did it have phones plugged in ir guitar plugged in?


Sent from my iPhone using Tapatalk

[thehallofshields]

I'll look around for some schematics, but I doubt it will be an easy find. The only one I can find is for the Crush 15r which has been posted here before.

I had the guitar plugged in, on its stand. The amp was set to a pretty low-medium volume. Left it for about 5 minutes, came back thinking I must have accidentally turned it off.

[thehallofshields]

Roly,

The Switch and the Fuse have both been checked with a multimeter, and they appear to be fine.

I've also tested the Diodes in the Rectifier section on the Diode Test setting of the Multimeter, and I couldn't find any problems. - However I did this while the amp was unplugged.

I understand you right, I should have the amp plugged in and test that the Transformer Output is around AC18v as the sticker on it says it should be. Then I should check the Output of the Rectifier, so see if I get the same Voltage, minus several volts to account for the voltage drop across the diodes; I'm gonna guess I'm looking for about 15v?

[J M Fahey]

How many wires on the transformer secondary?
Any labels/colurs?
A picture would be fine.

[thehallofshields]

Okay! Interesting discovery: No Voltage at the Transformers Output.







There are 3 wires on the connector, 2 blue AC wires and 1 black Ground. I get 0v AC whether the connector is plugged into the board or disconnected or whether the power switch is on or off.

[Enzo]

At the bottom of the photo is the primary side of the transformer - a blue and a brown if I read the label well, the brown looks kinda red in the picture.  The brown goes to the switch, and the blue to the AC block.  It is a bit hard to see, but it looks like one wire is not on a connecting posts at the AC block.  It sits at an angle between the switch and the AC block???


Otherwise, is there 120vAC between the brown and blue wires?

It was suggested by Roly, and I am going to ask as well, with one difference:  did you measure for continuity across the transformer primary.   I see no reason to exclude the power cord.  Connect the power cord to the amp, but do not plug it into the wall.  Hold the male end in your hand and set your meter to ohms.   Turn the power switch on the amp to ON.   Now measure resistance between the two main prongs of the power cord plug.  Not the third earth prong.  You ought to get some lowish amount like 50-200 ohms I'd guess.  What we don;t want to see if open.   Flip the power switch off and NOW it should read open.   If you never get the low resistance, then pull the power cord off and measure resistance between the two main pins of the power cord connector.  get continuity?  FInally, go inside the amp, pull those brown and blue wires off the switch and AC block and measure resistance between them, should be that lowish number.  We are looking to see if the main transformer primary is open or not.


An open primary is a lot more likely than an open secondary.

Now if your primary itself is not open and the secondary is intact, then look to the mains wiring.  Aside from a bad power cord, those other AC things could be bad.  Switch measures low resistance?  Fuse might be OK< but what matters is it completes a circuit through the AC block.  Is ther continuioty from the IEC male pin to the switch post, and from the other IEC male to the transformer lead?

[DrGonz78]

+1 to Enzo on mentioning that out of place looking terminal plug. I looked right at that pic too and it seemed disconnected or something.

[thehallofshields]

Okay, I'm certain the mains switch is fine. I've also tried 2 other power plugs.

When it's plugged in and off, I read 0 Volts (negative clipped to chassis ground) on the brown wire terminal, when it's plugged in and on, I read 119.3v.

When unplugged and off I read an infinite resistance, and when unplugged and switched on I read 19ohms resistance.

Sorry about the crappy picture; the 2 unplugged connectors go to the speaker, they are still zip tied to the other wires but I should have moved them out of the way.

However: I measure Infinite Resistance (at the 2mega-ohm setting) between the positive and negative wire of the transformers input. Do you call the Transformers Input the Primary and the Transformers Output the Secondary? Do I have a bad 'primary'?

[Roly]

When unplugged and off I read an infinite resistance, and when unplugged and switched on I read 19ohms resistance.
...
However: I measure Infinite Resistance (at the 2mega-ohm setting) between the positive and negative wire of the transformers input. Do you call the Transformers Input the Primary and the Transformers Output the Secondary? Do I have a bad 'primary'?

These two observations appear to be contradictory.

"Primary" input mains side.
"Secondary" output amp side.

A definite "maybe" (see above).


Note "THERMAL CUTOFF 130°/2A" on the top of the transformer.

With the amp unplugged check the transformer primary (mains side) directly for continuity on the transformer leads.

These thermal fuses can fail due to a fault, but they can also fail just because they feel like it, and they are not repairable.  If the primary is open circuit I'm afraid you need a new transformer.  Thankfully an 18-0-18V @ 1A is a fairly common component.  You will need to do some other tests to determine if this was caused by another fault or just a simple thermal fuse failure.

I understand you right, I should have the amp plugged in and test that the Transformer Output is around AC18v as the sticker on it says it should be. Then I should check the Output of the Rectifier, so see if I get the same Voltage, minus several volts to account for the voltage drop across the diodes; I'm gonna guess I'm looking for about 15v?

18VAC each side of the centre tap less a diode drop of around 0.7V is 18 - 0.7 = 17.3.  When rectified this will give an unloaded voltage of root(2) times, or 17.3 * 1.414 = 24.5VDC (roughly, a bit less depending on the idle current drawn by the amp).

[thehallofshields]

These two observations appear to be contradictory.

I was referring to the switch. When the Switch is on I read 19ohms resistance. Maybe that's enough to drop the 120v down to 119.3v that I'm reading at the switch terminal. Either way, it doesn't seem to be a problem. - I'm sorry for the confusion.

I'm really struggling to understand what I should be checking to determine if I need to replace the transformer.

1.) How can I check the wires for continuity? - One side of each wire terminates inside the transformer which is wrapped in tape.

2.)What resistances should I be reading between the wires?

[thehallofshields]

18VAC each side of the centre tap less a diode drop of around 0.7V is 18 - 0.7 = 17.3.  When rectified this will give an unloaded voltage of root(2) times, or 17.3 * 1.414 = 24.5VDC (roughly, a bit less depending on the idle current drawn by the amp).

Wow. I didn't realize that rectification increased voltage. Makes sense though. I'm not very mathematically inclined; how did you get 1.414?

[g1]

However: I measure Infinite Resistance (at the 2mega-ohm setting) between the positive and negative wire of the transformers input. Do you call the Transformers Input the Primary and the Transformers Output the Secondary? Do I have a bad 'primary'?

Yes, the input is the primary, output is secondary.  From your picture, the input is the red and blue wires on the one side of the transformer.  If you are measuring infinite between that red and blue, then the transformer is dead (open primary).

[Roly]

1.414 is the square root of 2.  The voltage coming out of the secondary is given as the Root Mean Squared or RMS voltage which is the DC equivalent (identical heating effect), but a rectifier diode plus capacitor produces an idle voltage equal to the peak voltage.

The relationship between V_RMS and V_peak is;

V_RMS * root(2) = V_peak

root(2) = 1.414...

so

V_peak = 1.414 * V_RMS

{The square root of 2 is equal to the length of the hypotenuse of a right triangle with sides of length 1.  It is also an "irrational" number like Pi in that it goes on forever and cannot be finally resolved to an accurate value.  Thankfully for electronics three decimal places is normally more than sufficient.  If you're into electrical/electronic technology at all it is worth memorising "fourteen-fourteen"}


The transformer consists of spools of wire, primary and secondary, insulated from each other but magnetically coupled.  (in your case the secondary also has a connection half way along brought out as the centre tap).  To your meter ohms range that's what they look like - just long lengths of wire.  If the thermal fuse (buried inside the transformer windings) in series with the primary has opened then you won't find any continuity through the primary side.

If the fuse (and winding) is intact there will be a lowish resistance.  It's hard to predict an exact figure but the 19 ohms to previously mentioned would not be unreasonable.  I just measured the resistance of a similar transformer with a 240V primary as 165 ohms, so whatever; you should be getting less than that across a good 115V primary.


"120v down to 119.3V" is actually well within the error band of your meter.  If you look at the booklet that came with it you will find that somewhere it says something like "accuracy +/-5%, +/-1 digit".  Or it might be 3%, but it won't be any better (unless you paid over a hundred dollars for it).  All readings are +/-1 digit simply because it's a digital instrument.  The accuracy of the analogue portion is generally about 5%.  This means that for an actual 120V in, valid readings could be anywhere between 120+5% and 120-5%;

120 * 1.05 = 126V

120 * 0.95 = 114V

119.3/120 = 0.99416667 or about 0.6% low, so you're splitting a hair that is around five times finer than your meter is capable of resolving.  0.5% is lab instrument standard and you are not going to pick one of those up for $5 or even $50.

But hang on, this means that the display is a lot more accurate than the actual reading!  That's right.  It's what we call "spurious accuracy" - the display is a highly accurate indication of a fairly rubbery value, similar to using a micrometer on sponge rubber.


tl;dr
Disconnect the transformer primary connector and measure the resistance of the transformer primary.  Open circuit?  New tranny.  Less than 200 ohms?  You have an open elsewhere else.