From james_eaton@btopenworld.com Sat Oct 13 16:41:20 2001
Subject:VK-7 spontaneous reboot (long technical post)

VK-7 fans,

For as long as I can remember, although not funnily enough in the first year
of ownership, I have had problems with my 1997 VK-7 spontaneously resetting
itself. It has done it about once every couple of hours, although it hasn't
done it much lately, probably because winter is approaching and the heating
has been on (see later).

To get to the point, I decided to take the back off my VK-7 and ferret
around the power supply (labelled "PS Board") near to where the mains comes
into the unit. I proceeded to wiggle the heatsink. Sure enough, the unit
reset itself! Funny that... So I took the PS board off the main chassis
(the top of the organ), un-did the heatsink screws retaining the 3
regulators and undid the circuit board screws which seemed to be loose.
Beneath each of these four screws attaching the PSU circuit board to the
heatsink was a circular metal solder pad. I seated these back onto the
heatsink and tightened the screws to ensure a good electrical connection.
When I had reassembled the unit, Iwiggled the heatsink again and no reset
occurred. This may be the solution to the VK-7 reset problem. I will
report back to the list if the problem ever occurs again. For the time
being I will test by leaving the unit on set on a programme other than 1-1
for a few days to tell whether it resets or not.

Possible explanation - screws not done up tightly enough in the first place.
Change in temperature of unit following use causes expansion of
metal/circuit-board and corresping break in electrical connection between
the earth on the PSU circuit-board, and the earth on the rest of the organ
leading to spontaneous reboots. It would appear that the VK-7 is designed
so that the printed pads at each corner of the PSU are the only connection
from earth on the PSU to earth on the rest of the organ. Earth from the
mains supply is attached to the chassis and not the PSU board.

This is somewhat embarrassing as I should have spotted it earlier, although
the 25 or so screws that hold the cover on the bottom of the instrument are
quite a deterrent from opening it up!

Also of interest:
- My PS Board is v1. Later models may have a more reliable connection
between the board and the chassis (e.g. a wire)
- The battery back-up on the main board is the pretty much standard lithium
CR2032 type which is easily obtainable. The unit in my VK-7 is made by
SONY, so I would expect it to last a while longer. With the unit switched
off, the voltage read 3.115v which seems pretty healthy to me for a nominal
3v lithium cell after 4 years! Is this information also available in
diagnostics mode ? A similar unit on my Yamaha rhythm unit lasted exactly 5
years, and it was actually soldered into place!
- The step-down transformer in the power supply has taps at 100, 120, 230
and 240v, so making the unit run on a different voltage is simply a case of
moving the brown wire adjacent to the voltage labelled with a red spot to
the appropriate voltage for the new region. And of course obtaining a new
power cord.
- A large inductor on the power inlet board (labelled "VK-7 Inlet Board")
would seem to indicate that the unit has some level of power spike immunity
which saves buying an external filter.
- Other than the PSU problem, my VK-7 has behaved faultlessly and has
increased my respect for Roland's manufacturing quality. The rotary
fast/slow button has started to pop out of its hole occasionally now though,
but I would put this down to fair wear and tear.

Cheers

James