As I wrote about in The Gear Keeps Arriving!, I bought a Tascam M3700 32 channel automated mixing desk. I came across the desk via a craigslist ad where the seller listed it as not working, for $200. Since I already have a Tascam M3500 I was planning to buy the M3700 for use as a donor. The M3700 has the full meter bridge, which my M3500 lacks, and the boards are so nearly identical I could use the broken board to keep the M3500 working for longer. Considering I had just spent $200 on 8 spare channels for my M3500, $200 for a whole second console is a darn good deal.

The M3700, like the M3500, is a large mixing desk that connects to a 3U rack mounted power supply. The owner explained that the power supply (PSU) was continually blowing a specific fuse, Fuse 2. When I arrived to buy the console he went into some detail about his testing process. He said that he had some success running the console with channels 22 and 32 unplugged, he then added that even with them unplugged the fuse still popped but after a longer delay. He also said that a friend of his who was a Tascam tech person advised him to swap the 5A fuse with a 7A fuse.

Let me start by saying that upping a fuse to a higher rating is a universally bad idea and I do not recommend it for any reason. A fuse serves one purpose: To protect the electronics that follow it in the circuit. The designers have chosen the proper rating for the fuse to be above what the circuit will draw but below the amount of current that will hurt the circuit. Changing the value of the fuse puts all down stream components in danger. Don’t do it! The tech friend said that popping a fuse was common on units with the larger meter bridge since it draws more power then the standard short bridge. That may or may not be true but the fuse that was popping did not feed power to the meter bridge. The fuse that does feed the bridge doesn’t appear to have ever popped and the extended meter bridge is a Tascam manufactured option, not something from a third party.

With the issues the seller was describing I was of the opinion that the problem with the board was in the PSU. The seller, based on the information from the Tascam tech friend, believe the issue was somewhere in the console itself. Either way, I need the board only as spares so I handed over my $200 and went on my merry way. Disappointingly, the fuse in question powers the audio path of the console so while I could see the board was in reasonably good cosmetic shape I really had no way to know if it was in any way capable of passing audio which did make it a bit of a gamble.

Putting the obvious functional issues aside though, the board was actually quite a find. I’ve already mentioned that the console has the full meter bridge, not too common in the US, but it also had the seemingly impossible to find balancing kit and an add-on to the onboard automation system. So far as I can tell, this board is completely maxed out. No other options that I know of were available for purchase. I wasn’t aware of these add ons until I arrived to take a look at the board and I will admit I got pretty excited!

Additionally, the seller told me that the owner before him had the first 16 channels of the board upgraded with new opamps and also did a full refurbishment. The opamps are a somewhat common upgrade on these boards for people to perform these days. An opamp is a tiny IC that does, basically, the volume gain within each channel. It’s a relatively inexpensive way to improve/change the sound of the board and the previous owner upgraded all five opamps per channel. Since the board was open they also went through and cleaned all the gunk and crap that tends to accumulate after 20 years of life.

Once I got the console home it was time to try my hand at getting it up and running again. I was now starting to really hope it would be a simple fix since the board had so many extras. With my M3500 already in good working condition it did give me a good base to start testing with. More posts to follow!

Robert