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Slow relay switch on Emu blank-screen
Old 4 weeks ago
  #1
Gear Head
 

Slow relay switch on Emu blank-screen

I picked up an E-mu Vintage Keys Plus with the old blank screen problem. I've fixed a Morpheus that had the same issue by scrubbing the socketed ROM leads, so I was hoping it would be the same story. It turns out Vintage Keys doesn't have sockets for the voiceROM, just the EPROM.

I've heard the main issue with these units is that they are very sensitive to battery power at bootup, and will get the blank screen if that is even slightly off.

I've changed the battery, and verified that the preset RAM chip is getting 3.3v even when it's powered down. The 3.3v path continues past the RAM as well, and it's pretty hard to track through the multi-layer board without a service manual, but some of it does go towards the big, blue RY-5W-K relay. It's not 3.3v though. Much less.

That's when I started to notice that the relay would make a clicking sound when I turn the unit on, and it would happen at a significant delay, maybe 300ms or so. The delay time isn't constant, and it doesn't always sound like it's happening, but it might just be getting masked by the button sound when it happens fast enough. The delayed click time corresponds to black boxes appearing on the screen slightly later than the backlight turning on.

Does this sound like a bad relay? The clicking sound makes sense, but I've read relays typically operate in the 5ms range, so it 300ms seems odd. Corrosion on the contacts inside seems like a possibility too. I'll probably replace it anyway.

I tried swapping out all 6 capacitors on the main board, but still no luck.

I guess my only other options are replacing the EPROM with the updated version, and doing a recap of the power supply.

Any thoughts? I'd love to know where the battery power is supposed to be besides the preset RAM, but service manuals don't seem to be around.

Thanks!
Old 4 weeks ago
  #2
Lives for gear
 
Radardoug's Avatar
 

No, it sounds like software is doing a delay before switching the relay, but then not continuing to provide the screen with data. Or is it missing signals to the screen? Or is it the screen missing contrast voltage? This will often stop screens displaying. You need to dig deeper.
Found this page with more info.
http://www.polynominal.com/site/stud...keys-plus.html
Maybe contact them?
Theres also stuff about the Proteus power supply here, it may be a supply problem.
http://electro-music.com/forum/viewt...roteus&t=25815

Last edited by Radardoug; 4 weeks ago at 05:33 AM.. Reason: More info
Old 4 weeks ago
  #3
Gear Head
 

Thanks. That second link is great.

My PSU is showing +-13.5v instead of +-12v, and I'm pretty shure they use the same PSU. I might try rigging a spare +-12v&5v PSU I have laying around, unless that's a terrible idea for some reason.

Any clue what would cause the voltage to be wrong? I also noticed the multimeter showed a residual current for 10 seconds or so after powering down.
Old 4 weeks ago
  #4
Gear Head
 

Apparently the PSU is still for sale, directly from the manufacturer for $40. https://power.sager.com/snp-9031-3985274.html

There is also a recap procedure recommended by the manufacturer, as this was apparently a common problem. The only thing is, my PSU is missing all those capacitors, like it was a later redesign using the same PCB. The caps it does have don't match the values of the original.

I only paid $30 for the synth, so I don't really want to spend $40 on a PSU, but I that's probably the sane thing to do. I'll probably try replacing the existing caps.

I'm also tempted to mix a few external adapters to get the necessary 5v 0.3A, -12v 1.5A, +12v 2A rails, but that might be a little too ghetto.
Old 3 weeks ago
  #5
Gear Head
 

I decided to try a reflow of every solder point on the PSU. The two 13.5v lines that are supposed to be 12v have turned into 17.5v and 6.5v, and the PSU is making a hissing sound. A little scary, so I think I'm going to be patient and order replacement caps.
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