dannzomatic

Hello again, I was successful, yippee! Today I researched again whether it could be an APO problem, as CYBERYOGI suggested in another thread. I also got to the bottom of the missing LED, my PT-20 no longer had a diode in the LN2G, apparently someone had already soldered it out before me. In the course of this, I set about examining the voltage regulator department in more detail because the LN2G is housed here. I had printed out various circuit diagrams from a service manual for the PT 1 and the SK 1, from which I tried to find clues. It turned out that there are not quite as many transistors installed in the PT-20 as in the SK 1. The APO signal takes a different path in the PT-20 than in the SK 1. Then I tried to check all transistors again, especially in the power supply area. When I soldered out the D545, it turned out that it no longer conducts in both directions (diode test, base to emitter and base to collector). The location on the mainboard is called D545 and a D734 F3B NPN transistor was installed. I then replaced it with another NPN transistor and it worked. There are no more breaks in voltage and the rhythms run smoothly. By the way, I think the hi-hats caused the voltage dropouts, maybe a lot of amps are needed here, I don't know for sure. I swapped the missing LED LN2G for another one from the spare parts box. It doesn't light up, but the PT-20 works. I also played on it a bit afterwords, which is actually a lot of fun with the accompaniment. Here are two more pictures of it. Good luck to you too! Best regards, Daniel P.S. I marked yellow the faulty transistor in second picture.

Hello, I welcome all long-standing members to this forum and am happy to be part of it now. Coincidentally, I also started reviving a Casio PT-20 around Christmas. My PT-20 also makes similar sounds to yours, Etaoin. If necessary I can also upload an MP3. After trying all sorts of things for the last 8 hours, I think it's time to join the thread. Maybe we can achieve something together to get the PT-20 fit again. The PT-20 means a lot to me and I would be happy if I can get it working again. I replaced the electrolytic capacitors a long time ago, but that didn't bring any improvement. Today I took all sorts of measurements and unsoldered and measured some transistors, ceramic capacitors, diodes, etc., but unfortunately I couldn't locate the error. For me too, the PT-20 behaves in such a way that as soon as the rhythm is on, the voltage collapses. For simple rhythms like the Waltz, only the LED gets a little darker at the low frequencies. With Ballad the PT-20 breaks down completely and the LED goes out completely. The PT-20 is still on because when you switch back to Waltz, the sound and the LED return. The chords sound good. But the presets all have a small punch in the envelope. They do that “uuaaap” at the end. Exactly how pianokeyjoe described it. OK. I'll leave it alone for today. If I can help building a schematic or do some measurements, let me know. Best regards, Daniel