Emu XL-7 & MP-7 User's Group

A couple of months ago a friend's beloved XL7 suffered the old problem all of a sudden, and failed to switch on. The machine didn't exhibit any strange behaviour beforehand. The only thing we could think of was that maybe filling up the 4th ROM slot had somehow overloaded the PSU? My friend always used the rear switch to turn the unit on/off.

The PSU was tried in my known working XL-7, and it didn't work.

I checked the PSU with a multimeter. The internal fuse was not blown. The 10VDC signal was present and the standby voltage 3VDC? was there, but no other voltages were present.

These PSU's seem to be impossible to find as spares. The PSU was apparently made specifically for these units (XL7, MP7, PX7, P2500) by PowDec Corp., it is a model CMG9-01. 

Sent the unit to a specialized synth repair place in the UK who were very confident of a reasonably fast fix. Unfortunately, after a month they still hadn't reached a firm conclusion of what the problem was so I got the unit back and sent it to a PSU repair specialist, Lazaros of Olympus Electronics in Wirral, UK. Lazaros promptly identified a problem with one of the large metal film resistors and other components. He quoted less than £50 for the fix, including the postage back to me. Their website and info is below:

www.olympus-electronics.co.uk

From what I understand, which is not a lot :) about these PSUs, they work just like PC PSUs, and instead of using a large transformer to take mains AC down to the lower DC voltages, they instead switch the current on and off very fast to convert a high voltage to a low voltage (hence the term 'switching power supply'). This enables the use of much smaller transformers and a more efficient, cooler power supply. The circuit that controls the fast switching on/off of current is the PWM controller.

And as I understand, this PWM control circuit was to blame for the problem here. Other than that, I don't know exactly which components were to blame. I would have a peek but there's a warranty sticker preventing me from doing that now :)

I am happy to say that as soon as I got the PSU back, I popped it into the XL7 and everything works perfectly now. Olympus Electronics did a fine job, kept me informed promptly, had a no fix no fee policy, and fixed it perfectly, I can't recommend them highly enough.

Now I wonder how long it will be before my own XL7's PSU needs repairing - it does seem to be an issue with these PowDec units... but at least there's hope now!

For what it's worth, I keep my own XL-7 plugged in and powered on at the rear constantly, and only ever use the front panel soft on/off switch. Everything seems OK with my unit - I did notice that the resistor in question was discoloured quite a bit on my (working but never repaired) PSU though.

Matt

--- In xl7@yahoogroups.com, "retroillumination" <r
>
> Sent the unit to a specialized synth repair place in the UK who were > very confident of a reasonably fast fix. Unfortunately, after a month > they still hadn't reached a firm conclusion of what the problem was 
> so I got the unit back and sent it to a PSU repair specialist, 
> Lazaros of Olympus Electronics in Wirral, UK. Lazaros promptly 
> identified a problem with one of the large metal film resistors and 
> other components. He quoted less than £50 for the fix, including the 
> postage back to me. Their website and info is below:

Great to hear someone has gone down this route succesfully! The type of switchmode power supplies used in the XL-7 are not rocket science and as you say the same technology is used in every PC - or indeed any piece of mains powered electronics these days. Normally it is not worth repairing them which is why people go for replacements 99% of the time, and hence knowledge about repairing them is scarce. £50 is probably what you would have had to pay for a new one anyway (if you could find it).

Another alternative is to find a compatible power supply, but I think people who have tried that have found that it is not easy to find something that matches well enough, plus it will most likely need modification of the XL-7 in order to mount it, plus new cabling ... a bit of a hassle at best.

As to why the power supplies fail, well, some of the components in there are under a lot of stress, and at the same time being a commodity item the only way to be competitive is to lower the price, resulting in some components having marginal specifications.

Great to hear it's working again anyway!