SPX 90 MK2 issues. Already recapped PSU.

Hello

I was just donated a dead SPX90 mk2.

This unit shows no signs of life. I have recapped the PSU as suggested in numerous other threads here.  When I check the PSU voltages unloaded they appear correct.  i.e +&- 18v & 5v

The led 7 seg display is dead as is the lcd & the back light. 

When I check the 7815 & 7915 on the main board I'm only seeing about 9-10v on the inputs to these devices.  All this is telling me that the issue is still power related.    On the PSU diagram there is an opto coupler PC2 which has it's output feed a connector to the main board. Does anyone know if this delays power on ?  I don't have the diagrams fr the main board.

Or any other common problems ?

Update

Optocoupler PC2 appears to work.

However all power rails are dropping on load.  +&-18v wind up around 9-10v respectively & 5v is about 2.7v.  Weird that all 3 rails are dropping ?

OK, nobody has had this problem.

Does anybody have the diagram for the main board ?

http://elektrotanya.com/yamaha_spx90_sm.pdf/download.html

Thanks for that Taram101.    I'm guessing the difference between a MK1 & Mk2 is just some chip upgrades.

OK got it.

This issue was R18, a 1k5  in PSU open circuit.    This meant that unloaded the PSU had the correct voltages, but loaded both analog & digital PSU rails sagged to the point there was not enough V for the digital side to work.

Rob Flinn said:

Thanks for that Taram101.    I'm guessing the difference between a MK1 & Mk2 is just some chip upgrades.

Click to expand...

Bigger dynamic RAM chips and different EPROM.

analogguru said:

Rob Flinn said:

Thanks for that Taram101.    I'm guessing the difference between a MK1 & Mk2 is just some chip upgrades.

Click to expand...

Bigger dynamic RAM chips and different EPROM.

Click to expand...

People seem to say that these are less noisy than the ver 1.    Maybe that means there are some other upgrades, since RAM & Eprom surely wouldn't provide a sonic upgrade.

Rob Flinn said:

analogguru said:

Rob Flinn said:

Thanks for that Taram101.    I'm guessing the difference between a MK1 & Mk2 is just some chip upgrades.

Click to expand...

Bigger dynamic RAM chips and different EPROM.

Click to expand...

People seem to say that these are less noisy than the ver 1.    Maybe that means there are some other upgrades, since RAM & Eprom surely wouldn't provide a sonic upgrade.

Click to expand...

What people seem to say.....
At least they are so similar that you only need to change the 6 DRAM-chips (4416 to 4464) and the EPROM and a v1 will act like a v2.