Help diagnosing a Roland SDE-1000 digital delay (guitar/bass/vocal processor).

[gooseEL34]

Hey gurus (or is it gurii ?)

I am somewhat knowledgeable about electronics.  I can read and trace a schematic, troubleshoot to an extent, and have a HP 206 sine generator, a Fluke 77 and a old Tek scope.

I have a Roland rack mount SDE-1000 digital delay meant for the guitar/audio world.
It was having an odd symptom in that the delay time (which is variable in 1ms increments with a up/down rocker switch), was behaving badly.  Specifically, it would not hold the specific delay time (for example, if I set the delay to 300 ms, it would float up to 310 and fall to 270 etc...).  More often it would fall than rise.

I suspected something with the power supply.   As I do not know exactly how a audio signal delay works, I looked for impaired parts, burnt resistors, scortched PCB traces, blown electrolytics, to no avail.

Is there anyone out there willing to walk me through a diagnosis via emails?  I can read a schematic and usually find the part on the board, so if someone said (put a 1k 250mV sine into the input and check the junction of C14 and R123 and you should get 12vDC, that is totally within my ability).


Schematic and service notes are here:

http://www.synfo.nl/pages/servicemanuals.html  and scroll down to the Roland section and save the SDE-1000 PDF

Owners manual is here:

media.rolandus.com/manuals/SDE-1000_OM.pdf


Probably best to do it off forum, so my email is timrichter9@gmail.com

[HalfSpace]

Hi gooseEL34,

I can give you some help to diagnose the fault in this device but why do it off the forum? I think other forum members might benefit from the topic.

HalfSpace 

[techricky]

I may be able to help as I have an SDE3000 here in the workshop, ok not the same unit but looking at the schematics, it uses similar functional circuitry.

I had a quick play with it and the displayed delay time is actually derived in part from measurement of the clock signal,  generated by VCO circuitry which is IC23 on the schematic (page17 of that manual link posted).

So if the displayed time is varying it is most likely due to variation of the VCO control voltage (as buffered by IC 24/2). Or perhaps more likely, the delay time scaling control pot, VR1, on the back panel as this is designed to have a large effect and if it was dirty/faulty could lead to big drifts in the delay time, it may just need cleaning!

Test for a stable voltage at IC23 pin 2 (for the 1 to 1.5times delay back panel control) and pin 13 (for the modulation and external control inputs))

[techricky]

Oh and check the power supply rails as marked (lower left schematic) for voltage and excessive ac ripple, it's highly likely that the main power supply electrolytic capacitors will need replacing. One in mine had leaked a bit underneath and corroded away the vfd power feed stopping the display from working, which is how I ended up with the unit   

[gooseEL34]

Ok guys.  Thanks for the responses.  I will be diagnosing and trying to repair this over the weekend.
I will post questions and pics as they come up
Thanks!!!