Usl cm-680

[Harold Hallikainen]

On the old forum was a question about the old USL CM-680 that is no longer supported. I just got the schematics and, based on the described symptoms, still suspect the power supply. There is an open frame switching power supply that provides +/- 12 VDC and +5 VDC. It also has a fuse on it, so perhaps that fuse has blown. Do the front panel LEDs work? Does anything work when the bypass power supply is present?

Again, I'm not really familiar with the CM-680. I did a lot of the design of the CM-8E, though.

Harold

ps - Interesting how the forum software changes upper case characters in the subject to lower case...

[Mark Gulbrandsen]

I have had several of those supplies fail over the years and I am pretty sure that the supply is obsolete. I got the last one NOS off of Ebay.

Mark

[Harold Hallikainen]

Interesting! I have never seen one that failed, but I clearly do not see everything. I can't tell from the CM-680 schematic what supply it is, but the pin out looks the same as that in the JSD-60 and JSD-100. If indeed the supply is bad, and it's not the fuse on the PS board, it should be possible to get a replacement. My guess at bad supply is just a guess based on reported symptoms.

Thanks!

Harold

[Ken Lackner]

Hi Harold,

The LEDs do light up, although the column of meter LEDs is lit all the way up regardless of activity. Obviously that is suspicious and I would be surprised if it is a coincidence. I think I forgot to mention this in my original post. Center channel works when the backup supply is connected and the crossover card is flipped to Bypass.

[Mark Gulbrandsen]

Harold, I remember two failure modes.... One was just flat dead and would not power up. The other two both came up and then shut off randomly. Powering it down and back up again then it acted dead. Like an intermittent power switch. Let it sit several hours and it would turn on again. I always suspected the capacitors, especially that large AC input cap.

Mark.

[Harold Hallikainen]

OK, if any LEDs are lit, PS fuse is obviously ok. Perhaps the -12V PS output is bad. That would bias the input to the VU circuit up lighting everything.

Harpld

[Ken Lackner]

Harold,

After your last post about the power supply, I was hoping this would be an easy fix, but unfortunately no such luck. The power supply seems to be fine, as I am getting +12, -12, and +5VDC. What else could I check for?

[Ken Lackner]

Another minor detail that goes along with strange LED behavior is that the "Processor" LED remains lit whether I have the monitor selector switch flipped to Processor or Amplifier. The "Amplifier" LED behaves normally in that it shuts off when the switch is flipped to Processor.

[Harold Hallikainen]

Email follow up sent.

Harold

[Miguel Moreno]

I have similar problems with my CM680s. I have noticed that they turn off when you have the monitor volume high and a loud sound is heard in the movie, which causes the equipment to freeze and the room to be left without audio.I also notice that the LEDs of the button with which the audio of the processor or amplifiers is selected stay on at the same time. is there any solution?

[Harold Hallikainen]

Unfortunately, I have very little documentation on the CM-680 (what I have is a modification to get rid of a pop when switching between processor and amplifier). PERHAPS someone else has something. The 680 was designed before I joined USL. I did a lot of work on the CM-8E, but not the 680.

Good luck!

Harold