A fix for trailing distortion after every effects based patch on JD800

This post cames from the Facebook Group Roland JD-800 / JD-990.

Our colleague Igor Kopman posted about the problem, and here what appears to be the main trouble, so he posted this first solution:

"Hi guys. Many people have Trailing distortion after every effects based patch on JD800. This is the DAC problem. Very easy to fix. Just replace the R100 resistor to another with a lower resistance on output board, and the problem will gone."

Here's the board: 

The circuit:

470k. Color code Yellow Violet Yellow Gold:

This one: 

Pay attention to this:

Our colleague Julian Camp replied:

Igor Kopman the original resistor has to be measured out of circuit. Do you still have your original and what does it measure? The schematic and colour code says it should be 470k

So after more replies from many colleagues in the group and thanks to  Igor Kopman  for presenting this need, Julian Camp posted what appears to be a more simple solution: 

Julian Camp

Replace VR1 with a high quality multi turn pot and it will fix the issue. The original VR when turned all the way counterclockwise or clockwise reads around 440ohm. The VR wasn't going low enough in resistance. Resistors R100, R101 and R102 tested within spec.

Thanks to everyone for supporting this great music machine! I love this synth and all you!

Manuals available: 

If you need the JDs Service Manuals plus all the others JD' manuals just enter at this page:

Manuals: JD800 and JD990 (Updated)

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The original topic text messages for credits, many people helped for sure!

** Igor Kopman

Hi guys.  Many people have  Trailing distortion after every effects based patch on JD800. This is the DAC problem. Very easy to fix. Just replace the R100 resistor to another with a lower resistance on output board, and the problem will gone.

** Radek Tymecki

You think that changing the resistor is the key? Caps are ok?

** Jym Mccullough

Can you be more specific on "lower resistance?" How about an exact value that works?

** Kevin Nolan

Jym Mccullough It looks like a 46 Ohm Resistor - hard to tell but I think I'm seeing Yellow-Blue

** Igor Kopman

Jym Mccullough I will open my JD800 and check it.

** Igor Kopman

Jym Mccullough Ok the resistor is 137k

** Kevin Nolan

Igor Kopman Yup - 46 Omhs - 137k - I was almost right 🥴 (ye know - on the cosmic scale of things...)

** Julian Camp

Igor Kopman the original resistor has to be measured out of circuit. Do you still have your original and what does it measure? The schematic and colour code says it should be 470k

** Igor Kopman

Julian Camp I think it was 240k or 270k

** Julian Camp

Igor Kopman that's what it would measure in circuit. Did you measure it out of circuit?

** Julian Camp

You have to take the resistor out of circuit to measure it. Mine reads 480k. The schematic and colour code shows it should be 470k. So this resistor shouldn't be the issue unless my cheap meter is correct and it is 10k out of spec. Will replace with a … Ver mais

** Julian Camp

470k. Color code Yellow Violet Yellow Gold

** Gilberto Strapazon

Thanks Igor Kopman!

Please, you or someone else with the same trouble may check about the measure out of the circuit of the probably damaged part?

This topic will be replicated at the JD800center if we have more info.

Appears the kind of problem with a easy solution and this means Gold!

I'm saving all the topic (with all replies for credits) for a post at my site.

I'm sure many people will be after this information too.

Thanks for more replies so I will soon post at the JD800Center too.

** Jym Mccullough

Gilberto Strapazon Thanks for maintaining your website. I've looked there many times for info and tell others as well.

** Julian Camp

I will replace the three resistors going to the trimmer pot and report back. Will be replacing with original values. R100 - 470k, R101-1M, R102-200k.

** Eric Vaubel

My JD-800 and my PCM-80 both do this. Will investigate!

** Julian Camp

UPDATE!

Replace VR1 with a high quality multi turn pot and it will fix the issue. The original VR when turned all the way counterclockwise or clockwise reads around 440ohm. The VR wasn't going low enough in resistance. Resistors R100, R101 and R102 tes… Ver mais

** Gilberto Strapazon

Julian Camp great! Simple and very effective!

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