Akai GX-280D-SS playback speed issue

[quadsearcher]

Yes this gets a little past the hobby zone, closer into the electronics technician zone. Big reel decks almost insist upon servicing in place, can be risky to move, and it can be hard to find a tech who knows real circuit-level service,.
However, being in the LA area, I'm sure there's more than several and the bonus is that the right ones know the other stuff to look for thoughout the unit besides the present problem.

 

[Derek_Ronin]

With it looking like it was previously worked on, I probably should bring a printed schematic and have a professional who is better at this. Had my hopes up thinking that I could tackle this.

 

[Derek_Ronin]

Tested the power transformer leads (Orange/Orange 26v winding) out of curiosity. Getting a reading of 29v.... a few voltages off-spec. I don't suspect a faulty transformer since everything is powering up. Will probably need to look into the power supply block. Perhaps the electrolytic caps there are causing me problems? Values are (1 x 220uf @ 160v) , ( 1 x 100uf @ 160v) and ( 1 x 1000uf @ 50v)

 

[par4ken]

Tested the power transformer leads (Orange/Orange 26v winding) out of curiosity. Getting a reading of 29v.... a few voltages off-spec. I don't suspect a faulty transformer since everything is powering up. Will probably need to look into the power supply block. Perhaps the electrolytic caps there are causing me problems? Values are (1 x 220uf @ 160v) , ( 1 x 100uf @ 160v) and ( 1 x 1000uf @ 50v)

View attachment 91590
View attachment 91589

Unregulated voltages are nominal. They can read higher or lower depending on the actual line voltage.

 

[Derek_Ronin]

Thanks for the clarification, then looks like everything from bridge rectifier forward and before trimpot still seems to be my issue. 1k trimpot came in, so figured I might as well pop it in and take some readings. Getting about 37v to the B+, going to swap a proper 5k and 10k and take some readings on the B+ to see if any effects. Might as well, since kit came with a few values to experiment with before I take it someone close by that can work on these.