Next Roland TR-909 vintage analog drum machine came for repair in with „no attack“ on the bass drum. But also had some more minor problems such as the mains plug, dirt potentiometer etc, so I suggested a full refurbish on this one and thats what I did.
I start to disassamble the TR909 and replaced the mains input jack with a NOS I had in my stock. Then I looked into the schematics to find out, why this TR909 had no attack. Transistor Q5 gave me the trigger signal but Q6 wasn´t triggering the noise signal (base). So I looked for bad solder joints or traces. I found these cracks on the pcb.
Simply a connection between these vias wasn´t there. So I fixed that with a kynar wire. And voila, now that bass drum has attack again.
Last but not least I found some resedue on the psu board which I checked for leakage. But it wasn´t leakage, just glue. But since some glue can become conductive over time I decided to clean that up and recap the psu.
That’s it. Roland TR909 is fully working and rock solid. Here are my usual pics I have taken for my own purposes and that I share with you guys.[/caption]