Need advice: broken Electro-Harmonix Qtron+

[guile]

Guys, I bought an Electro-Harmonix Qtron+ pedal. It's broken. Paid a couple of euros for it.
It sounds thin and lacks power to the signal. When engaged, there is a signal but it's very little coloured by the effect. The response is also weakened.

The former owner said that the adapter broke down too. This could be a clue...

I would love to be able to repair it!
Anyone ideas?

[hammerheadmusicman]

Have you had the back off? I've had a few EHX pedals where components have burnt out and scorched the board a little inside, both times near the power jack. Some high res pics may help..

George

[guile]

Thank you. Wil do that asap

[guile]

The strange thing is that sometimes it works flawlessly and then the effect-signal is gone for the most part.
I noticed that the footswitsh has been replaced. The led is also always ON, regardless if I engage footswitch or not.

Could the footswitch be the problem? Anyone ideas?

[electricstorm]

First thing I'd do is touch up the solder joints on the foot switch and go from there. If it is intermittent as you say, that is usually an indication of a cold solder joint. It doesn't necessicarily mean there isn't another problem but the solder joint on the switch looks suspect to me.

Let us know what happens after that.

[guile]

Alas, no change, no improvement...

The loss of effectsignal is in fact not that intermittent. The first 30 seconds or so it works fine but then stops reacting like an envelope filter should. It's kinda sneeky, hard to explain, but all that's left is very little effect and no more wap, wap, wap  

Anyone?

[electricstorm]

In that case, it could be heat related.

Be very careful with what I am about to tell you!!!!!

When you turn it on, wait till the loss of signal occurs then very quickly tap each IC and let it go. In other words, briefly touch the IC's (and transistors if it has them) and let go. Don't leave your finger on them in case they are hot. I have been burned quite badly once or twice doing this. What you are trying to determine is if the IC's/transistors are overheating. It would actually be better if you have an infra red thermometer to do this. If you have one, take a reading of the temp before you turn it on and again after you have loss of signal. The temp difference should not be but just a very few degrees different if it is good. If it is way off or you can't touch the IC/transistors without being burned or the IC/transistors are quite warm when touched, then this could be the problem and the IC/transistor may be bad. Replace the IC/transistor and see what happens.

Depending on how old the pedal is, you may also have some electrolytic caps that are bad or not properly working. Look at those caps for signs of leaking or bulging. This is usually a dead give-away that they are bad. The tops of the electro's should be flat and the bottoms should sit flush against the board with no yucky looking stains on the board or on top of the caps.

If you have an audio probe, probe the pins/legs and see where you are actually loosing the signal at. This might tell you where the problem is.

Let us know what you find.

Jim

[jeffaroo]

take a wood chopstick and tap the ics and listen as you go. hes right about burning your fingers, thats why i bend down and touch with my tongue (just kidding) if you have a decent dmm pull out the temp probe. still stuck ? poke around at other things with the ole chopstick. i used to have a old AC Memory man thing would shock you just for looking at it wrong !   

[guile]

Thanks guys I will check it as you say (even if it means burning my fingers).

The former owner mentioned that the adapter broke. Isn't that a clue?

[electricstorm]

If you are talking about the wall-wart adaptor for your power source, then it possibly could have damaged U6 (kinda looks like a 78L05 regulator). Take a volt meter and make sure you are getting the correct voltage on the board and also check the voltage at the IC's (pins 4 and . If U6 is a 78L05, then pins 4 and 8 should give you 5 volts.

Jim

[guile]

If you are talking about the wall-wart adaptor for your power source, then it possibly could have damaged U6 (kinda looks like a 78L05 regulator). Take a volt meter and make sure you are getting the correct voltage on the board and also check the voltage at the IC's (pins 4 and . If U6 is a 78L05, then pins 4 and 8 should give you 5 volts.

Jim

I tried the chopstick-method, but nothing is overheated.
Nothing is bulging or leaking either (I'm talking about the caps of course).
The '78L05 regulator' has about 8,5 volts running through it. Is that good?
All the IC's pins 1 and 5 have about 18 volts running through them (when the effect is on)


When I measure the adapter it reads 30 volts, but when I measure the input socket (directly after the plug of the adapter) it only reads 27 volts.
What about the fact that the led that is ALWAYS on even if I switch the switch off?

[patrickbrose]

A few bits of info:
1. The current Q-tron+ uses a 24VDC power supply. I have look through the web and that seems to be the consensus for all Q-trons. So if your PS is putting out 30VDC, then there may be a problem with it.
Can you post a picture of the label on the power supply itself?
2. The "regulator" that you tested, can you look at what is printed on it? It sounds like that is a 9v regulator not a 5v. Knowing the part number will help.
-P

[guile]

A few bits of info:
1. The current Q-tron+ uses a 24VDC power supply. I have look through the web and that seems to be the consensus for all Q-trons. So if your PS is putting out 30VDC, then there may be a problem with it.
Can you post a picture of the label on the power supply itself?
2. The "regulator" that you tested, can you look at what is printed on it? It sounds like that is a 9v regulator not a 5v. Knowing the part number will help.
-P

The adaptor that I use is from an EHX Qtron+ NANO; it works fine with that.

[patrickbrose]

OK, that helps. That is a 78L18 regulator (designed to regulate to 18V). You should see 18v on the output pin of that regulator. Post the voltages (DC) that you get from each of the 3 pins.
-P

[guile]

OK, that helps. That is a 78L18 regulator (designed to regulate to 18V). You should see 18v on the output pin of that regulator. Post the voltages (DC) that you get from each of the 3 pins.
-P

Middle: 18 volts
outer ones: 8,3 volts