Im a happy owner of an original QS4 since aprox 1994. Still working! Well, sometimes it has some "tuning flutuation" - either in the pitch bend potenciometer (resistor) would be my first guess or in some crystal/chip. I do have changed all the buttons and all potenciometers along the years. The display is failing, kind of hard to read, which seam to have been an issue on early models. But I still do like it! Working great to play on!!
Well, this year I bought an old used QS8.1. Since long wanted to have one. I have allready opened it and I can see it has been repaired or at least opened and dealt/messed with. Its all working as expected being quite old I guess.
I love it! Cant belive I have played on non-weighted keys for so many years. Still hanging on to my QS4 too though.
The aftertouch does not work but it does not bother me really.
Some keys are a little bit noisy and eventually I look into that later.
But for now, I have noticed that the Left Main Output is considerably lower than the Right one. Well if I set the Level to route to Aux instead both are equally low as the Left Main so maybe its the Right Main that is high. Not the Left Main that is low.
This if assuming that the Main Outputs should be of same volume as Aux Outputs.
Is that a right assumption? (maybe the EFX setup might implicate in diferent volumes)
The Headphone is good, both Left and Right channels.
Now, I have studied it inside and also the schematics 9-40-1387 ver C (not sure if this is the version I have). There does not seam to be a sound bump on powering on on either Main our Aux outputs which from what I have red could indicate a burnt J111 Fet transistor.
I noticed inside that there is two common resistors welded onto (parallell to) what I guess is the R32 and R26 resistors of 1kohm. (which I understand would not affect headphone since the signal is picked up before these resistors)
First I thought that some technician had thought that these resistors was burnt and welded this comon reistors onto them. Then if one was actually working, the result would be two parallell 1kohm resistors resulting in less then 1kohm, and therefore a higher volume. Am I reasoning right?
On the other hand, I have red on sites that some find its outputs low so the intention was maybe to raise the level by doing this on both channels but failing somehow on one channel leaving it low.
In any case, failing to weld properly one of the resistors with the intention to rise the ouput volume, or with only one original resistor fried, welding a resistor on both channels, either way would leave the levels "equally lower" on three outputs and high on one only. As far as I can see the Aux Outputs have been left unmodified.
Am I reasoning correctly? Please, any ideas, advices, help... is highly apreciated.
Another thought, would such a modification, in the intention to rais the output volume, so raising the current (less voltage over these resistors) then put into risk the U7A, U7B? (which a believe is transistors/amplifiers/ops)
I have no trustworthy service center nearby. Shipping it far away would also be far to expensive. So, if the only recommendation is take it to an Alesis authorized repair shop please dont bother. I am looking for people who understand the technical aspects here, and that could and will, offer some help.
I also have a parcial PCB print which follows the schematics PDF I have. I do wonder thou if anyone have a complete/full PCB prints/PDFs? I am looking mainly the for the PCB of the main baord. But would really like all of them, as all the schematics. Since I have to rely on myself and any willing remote assistance, these documents really help.
So, thanks for reading, taking interest and thanks so much in advance for any help!