Hi, months ago, after removing the inverter but not the Q25 transistor (which I then did later), the K2000 I have started to shut down after a few tens of seconds, then every time it was turned on, faster and faster, up to remain lit for up to a few seconds. Initially on the Audio/Power board.
I tested the electrolytic capacitors, unsoldering them, but they turned out to be fine. I also checked several diodes and resistors, same thing.
Then one day, during a further check (since I could no longer use it), after about 30 minutes in which I was intent on measuring the voltage on various integrators, connectors, etc ..., I see smoke starting to come out in the vicinity of the double Schottky diode D25.
I immediately turn off the K2000, but the problem seems to persist. Subsequently (I hadn't done it before because I was thinking of a completely different cause), I check the voltages on the transformer secondary and they are all wrong. Arrived today, a few months after those days and after having found a working transformer, I was able to do other tests.
Capacitors all work, but I replaced them. I've replaced several transistors (specifically the 2222A's and a couple of 2331's).
I replaced the D25 dual Schottky diode and the two voltage regulators next to the dual Schottky diode. Then before replacing the IRFZ20 mosfet with an IRFZ44 (following the advice of more expert people), I heard an unpleasant noise and I found that the track that connects the central pin of the mosfet to the positive of the capacitor C202 was blown.
Once the track was re-welded, the problem no longer occurred. Compared to months ago something, albeit minimally "has changed", because the display shows a few lines but not the writing. I measured the voltages again on all the capacitors (also on the Engine board), but in particular on the Audio/Power board, because it is the board that surely has problems and I found some that have no voltage across them, but not only , there are also some transistors that don't seem to be reached by any voltage.
The capacitors that have no voltage across them are those highlighted with an asterisk, while the others have voltages across them, but some in my opinion are a bit low (but maybe that's just my guess):
*C91 10uF 35v (no voltage across).
*C196 10uF 16v (no voltage across).
C2 470uF 16v (marks 4.5v)
C83 22uF 25v (marks 3.53v)
C114 10uF 35v (marks 3.6v)
C117 10uF 35v (marks 2.3v)
C120 10uF 35v (marks 2.3v)
C122 10uF 35v (marks 5.4v) (C114/C117/C120/C122, have these voltages only when the Engine board is connected, otherwise the voltages detected are the following:
C114 10uF 35v (marks 2.3v)
C117 10uF 35v (marks 0v)
C120 10uF 35v (marks 1.65v)
C122 10uF 35v (marks -0.2v)
C128 100uF 16v (marks 5v)
C169 100uF (marks 5v)
C176 10uF 35v (marks 0v)
C178 220uF 16v (marks 4.7v)
C182 10uF 35v (marks 15v)
C186 100uF 16v (marks 5v)
C188 100uF 16v (marks 4.5v)
C190 1000uF 25v (marks 21.5v)
C192 4700uF 25v (marks 21.3v)
C193 100uF 16v (marks 12v)
C202 22.000uF 16v (marks 6.44v)
C203 2200uF 16v (marks 5.3v)
C204 10uF 35v (marks 4.5v)
C206 100uF 16v (marks 12v)
C207 100uF 16v (marks 12v)
C208 4.7uF 50v (marks -0.74v)
I also replaced some transistors:
Q1 2222A
Q8 2222A
Q15 2222A (but there is no voltage on its pins). Q17 2222A (also no voltage is present here).
Q20 2222A (not replaced, but there is only a voltage equal to 0.64v on the base: the same base is internally connected to the positive of C202).
Q21 2222A
Q22 2907
Q23 2222A (replaced: marks -15 on pin 1, -15 on middle pin and 12 on pin 3).
Q24 2331
KF 351 (replaced with an LF351 and in both cases, both the KF351 and the LF351 output 0volt on pin 4 and 21.5 on pin 7: while these ICs should have max +/- 18v on that pin).
I specify that at the audio level nothing is heard and the LEDs do not light up.
On pins 1 and 3 of the double Schottky diode D25 there are about 6.7v alternating current. I don't know if it depends on the fact that the inverter has been removed, but I think it is no coincidence that the capacitors C92 and C196 have no voltage across them and then, the fact that the capacitor C202 has only 6.7 volts across it.
Also Q15 is connected to the positive of C202, but there is no voltage at pins of Q15 (and Q17). At the moment I don't have an oscilloscope to be able to do other tests (I still have to learn how to use it) and I don't have such knowledge that could be useful to me. I'm doing what I can, but it feels like a puzzle.
Another detail that I think may be relevant is that the positive of capacitor C202 is connected to the base of Q20, but the latter has a voltage of only 0.64v on the base. I add that sometimes, apart from the fact that I'm certainly not an electronic engineer, making comparisons is not easy, because some components are named differently in the service manual.
Thanks