Hi there!

Just an update on this, there is some kind of improvement. The amp works at least, but occasionally and randomly I get a fluctuation in the tone, sound gets very bassy and at the same time a static hum starts also. Then sometimes I hear a ticking sound in the speaker. All these don't seem to happen on very low volume.

I'll take it back to the repair shop. The guy says it could be a condenser that he missed.

I took it to a professional. He replaced the TDA and saw a broken track underneath. He fixed it with a wire. We turned it on, smoke and sparks again around the TDA. Then we noticed another broken track, it's actually visible in the last picture above, on the right side of the resistor. We fixed that one too, turned it on, no smoke anymore, just a loud pulsing hum in the speaker. It was late Saturday afternoon, the shop was closing, so now I'm waiting for further troubleshooting.

One step further. The TDA you mentioned before was actually hidden behind a cover that was pushing it towards the radiator. After taking that off, the root cause became visible quite spectacularly. We saw that it's a TDA7293 and it's all smoked and has a few pins completely burned off, see pics. My uncle then measured the voltage between pins 13 and 15 according to the TDA datasheet below:

http://www.datasheetcatalog.org/datasheet/SGSThomsonMicroelectronics/mXrqwxu.pdf

He got about 75VDC there and concluded that probably everything is alright up to that point. After taking off the board he measured all the capacitors as well and there was still electricity in them, so they probably survived as well. The only thing I'm worried about is the other small chip CTS0814, it has some smoke on the pins, but it's probably from the TDA blow.

Now I'm debating wheter to replace the TDA or the whole board. Seems equally difficult, cause the wire stripe is soldered directly to the board as well, it doesn't have a connector. I think I'll just find someone to replace the TDA first, since we don't have the proper tools. Then worst case, I'll go back to Line6 for a board. Wonder how much they will charge?

My uncle also said we could also replace with a TDA7294 (he actually has one at home), saying that it pretty much does the same thing as the 7293, but it's more resistant and can take higher voltages. Just in case I didn't learn my lesson.  :duh

Too happy too soon. The amp part is dead after all. There is a continuous hum in the speaker, that doesn't change when I turn the volume knob. It doesn't go off when I connect the headphones either, allthough that is suppose to mute the speaker. The headphones output works fine though, no hum in the headphones. My uncle is looking into it. The amp board is fairly simple, there are only a few parts on it and they seem replaceable. It doesn't show in the pics sent earlier, cause it's a bit hidden and I didn't notice it. I'll keep you posted.

Quote from: J M Fahey on June 15, 2010, 11:22:32 AM
I get what you mean.
You may add a ground lug under any screw which touches the chassis and use a long wire, with a crocodile on each end, and ground your amp anywhere available, such as a cold water tap.
The other (better) option would be to build a dedicated power strip, with the 220/110 transformer mounted on a piece of plywood, with a 3 prong cable that goes into the wall and a 3 hole socket for your amp, where the ground connection goes straight through, skipping the transformer.
You should also match neutral to neutral.
Both hots won't be directly connected, being that one is 110V and the other 220V.
If my explanation sounds confusing, tell me and I'll draw a wiring diagram for you.

I think I got it. The main idea, in simple words: I need to drive the amp's power chord ground prong into the wall socket's ground, right? All this with proper 3 prong/hole cable/socket

Got that, but I meant the transformer's power cord and the wall plug. Same for the 110 output, it has only 2 holes. So when I plug the amp's power cord into the transformer, the ground pin just hangs in the air. I was expecting it to have a dummy ground wire between input and output, bypassing the actual transformer, just to provide grounding for the amp.

I think I have some good news. I bought the 300W 220/110 transformer and the amp works fine on headphones. The chassis/speaker is with my uncle, going to retrieve it asap. At least I know the effects are OK.

Btw, the 220/110 transformer doesn't have grounding, is that OK?

No worries Phil, I don't hate you  You are only trying to help. I don't have the basics indeed, but I thought measuring a few things can cause no harm, as long as I keep my fingers away. And I only did that because I did take it to "professionals" first, but they gave me BS. So I had to go on my own, at least for the first part. I only wanted to know if the transformer is OK, so I can go for the 220/110 transformer or otherwise go with the original 160 EUR transformer (or a cheap replacement, if I could figure out the specs). I have my answer, I'll go for the 220/110 transformer. Which is actually a prerequisite for the next level troubleshooting. So that's it, I'm off of it, I will certainly do not replace any parts myself. I'll take it to someone, but I wanted to get some basic understanding so they don't BS me again.

Thanks for your help!  0:)

Quote from: J M Fahey on June 10, 2010, 08:07:59 PM

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NO NO NO NO NO NO NO .....................YOU ARE GOING TO DIE............................

  I think I was safe, I didn't touch anything directly, only used the tester.

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1) YOU ASSUME THAT SOME PRIMARY CONNECTION GOES TO GROUND, OR "IS" GROUND, IT IS NOT.
NEVER ANY PART OF THE PRIMARY IS OR TOUCHES GROUND OR ANY PART OF YOUR CHASSIS ..... NEVER.

If it's not ground, that I don't know what it is. This is what I did:

- unplugged all transformer wires from board
- only plugged the B&W wires to the board
- plugged the unit into a 220V-110V transformer (~25W), then into the wall socket (220V). So at this stage I had the whole transformer off
- then I measured all pin combinations on the 2 connectors on the board (where the B/R/Y wires should go). Since I didn't get any reading on the pin that I marked with G in combination with any of the other 2 pins, I figured that must be the ground. Then on the remaining 2 pins I measured 120VAC

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2) Your transformer does NOT have a 110V/220V primary.
It EITHER has a 100V/120V tapped primary (your case) OR it has a 220V/240V tapped primary (yours does not)

Yeah, got that.

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3) You need a 220V/110V transformer to use your amplifier.
4) Your transformer is fine, you just saved €160 or whatever.

I'm debating whether to buy a 220\110 transformer or a cheap replacement for the original transformer (220V version). To which I'm still not sure about all the specs (for example the 2 brown wires). The 220/110 transformer seems an easier option.

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5) Your amplifier is, VERY probably dead (sorry)  

Yeah, now at least I can go to phase 2 and still hope for an easy fix (a condenser or something). I think I'll just buy a 220/110V transformer and take it back to Line6 for further troubleshooting, so they can at least power it up and look further. Allthough their level of expertize is now questionnable, since their diagnose was that the transformer is dead. I'm granting them that they had to guess, since they didn't have a 220/110 transformer to power up the unit for measurements.

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6) In the VERY UNLIKELY case that your amp survived, just for peace of mind, replace all fuses as stated in the manual or the different labels (use those related to 120V), plug into a 220/110V transformer, size at least 150VA, preferably 250to 300VA and power it on.

One last question: since I don't have such a big 220/110 transformer yet, I had to use a 25W one. Now if I get the lights on and a hum in the speaker, is that a bad sign or a good sign? Is it suppose to work with a 25W transformer anyways or it just doesn't give enough juice to power the amp properly and maybe that's why I get the hum? Just for me to sleep better during the weekend, until Monday when I can buy a proper 220/110 transformer.  

Thanks Phatt!

I actually said that the 36.8V is AC, that's why I was surprised. If you check the diagram, I also stated there that all voltages are in AC. It makes sense now with blue/black/blue wires, but I still don't understand the two brown wires where I get the 10.2 VAC. Is that powering another area of the boards or something? So I still don't know what to ask for if I go to a shop. A 220VAC to 36.8VAC/10.2 VAC transformer, 75W? Is that it?

More pics, second board, transistors

The data I promised earlier. I draw a few sketches, took some measurements:

- first of all, I figured out what the 2 connectors (110/220V) on the motherboard are for. They simply drive the AC input coming on the B&W wires to different pins/wires (black/yellow/red) to be fed into the transformer. For 110, ground falls on the middle pin (red wire), while for 220 it falls on a side pin. It seems the 2 types of transformers have the input wires arranged differently. I figured this out by plugging the amp to 110V (via 220-110 transformer) and unplugging all transformer wires, then measuring the pins. See pic. Not sure this is correct, I thought ground is usually yellow, but this is what came out of the measurement.

- then I measured resistances on the transformer, see diagram

- I also measured the output voltage on the transformer and was surprised to get AC instead of DC. Is that correct? Values quite high also, 36.8V. So it seems the transformer survived, allthough not sure it's giving the right output. Either way, it's bad news for the amp part

- took some more pics of the boards, it seems I have an LM1086, an LM317T and another one MC7805CT. There is a DSP chip also.

Does it all fall into place? Is that 36.8V accurate or my tester is bad? I still wanna figure it out and buy a replacement transformer, so I can take it back to Line6 for further troubleshooting. I'm still hoping it's only a transistor or a condenser.

I'm still hoping for some kind of 3rd level protection, there are some condensers in the front line

OK, I'll send you the info. It is possible that the transformer survived indeed. This is what happened actually:

- I was mislead by the label on the back of the power unit, which kinda suggested that it's a dual transformer (see pic above). Should've looked it up first, but it was an honest mistake at the same time. If you check the Line6 forum, there are 2-3 cases every week with people repeating the same mistake over and over. So I replaced the fuse from T4A to T2A, plugged it into 220V and boom, the fuse blew. Tried with another T2A fuse, same thing.

- then the fatal mistake, I put back the T4A fuse and plugged it into 220V. The fuse didn't blow anymore, but I smell and saw smoke. I turned it off right away, it was on only for less than a second

- then I got a 220V-110V transformer, a very small one 25-30W. I tried with that one too, I got the amp display on and a hum in the speaker, but none of the buttons worked. So either there wasn't enough juice given by the 220-110 transformer or the amp transformer survived, but the electronics in the amp burned

Let me ask you, in theory, what happens with the output voltage of a transformer, if we double the input? Say we have a transformer 110V->15V and we plug it into 220V, will we get double on the output (30V)? If so, that's bad news for my amp, unless there is some kind of 3rd level protection there (in case neither the fuse nor the transformer blow).

I'm still hoping that the amp is fine and only the transformer died, for 2 reasons:

- I wanna trust what the Line6 guy said
- I think I remember my uncle measuring resistance on the output wires (blue, blue, brown, brown, black) and there was no continuity, so he concluded the secondary might have fried

I'll come back with the measurements you asked for.

Thanks, so what's next? Is this data enough to calculate the output voltage, which is the ultimate goal eventually? Or do I need to count loops also?