Tascam 48 Amp Cards

Things are coming together slowly, equipment-wise. I wanted to use my 1/2″ 8-track, a Tascam 48-OB, so I hooked it up to the mixer and went at it. Something was really wrong, though. I recorded something onto track 1 of the tape, and on playback, the VU meter on the deck looked OK but I was getting hardly any signal on my mixer. After running through the cabling and checking everything on the mixer, the cause of the problem appeared to be in the tape deck, but I had no idea what it was.

I posted a thread on homerecording.com and a few people suggested that it might be the relays on the amplifier cards. To be specific, there’s two relays on each amplifier card that control signal output. The 48 runs at either +4dB or -10dB, and these relays switch between the two sets of inputs and outputs. When they fail, they’ll often they fail simultanously, breaking on multiple channels. This made sense, as the problem soon spread to 4 of the 8 channels on the deck.

To make sure that its was the relays, I plugged the +4dB balanced outputs into a firewire interface and played a MRL testing/calibration tape several times, going from channel to channel each time. They all worked. This confirmed that it was indeed a problem with bad/dead relays.

After asking several more questions, I found out that the bad relays were the ones labeled “K003″ on the amplifier card. These relays are used when using the deck’s -10dB unbalanced outputs. The stock relay is an NEC component that is no longer manufactured, but a company called Hamlin makes a perfect replacement. It’s the HE721A2400, and it can be found at DigiKey for cheap.

Hamlin HE721A2400 Relays

Replacing the relays isn’t difficult but it requires some basic soldering skills. You will need a solder sucker; most decent electronics or hobby supply shops sell a basic model for $15-$20. Knowing how to use it is also important: I didn’t know how to use one and carelessly assumed that I could figure it out, and ended up damaging one of the cards (I repaired the damage, though). To remove a component from a circuit board, apply the soldering iron tip to the lead of the component on the “top” side of the board, while applying the solder sucker tip to the bottom of the lead on the “bottom” side of the board. When the solder appears to have melted, click the solder sucker and the molten solder gets sucked out of the drilled PCB hole and into the sucker. I wish I had a picture to demonstrate this, but reread the last sentence and ask any questions if it’s unclear.

After removing all of the K003 relays, I soldered IC sockets to the holes where the relays had been. I did this in case the relays need to be replaced in the future… saving myself or someone else some work. The relays snapped into the sockets easily. Here’s a picture of one of the replacement relays, in its socket:

Closeup of New Relay

I put the cards back into the deck, put the MRL tape on again, and everything worked just fine. I was so relieved to have it working again, and I was proud to have fixed it myself… with a lot of help, of course.

Notes:

• The Tascam 42, 44, and 48 share the same amp card design. This repair will work for any of these models.
• A full calibration should be done on the deck after replacing the relays. The relay’s performance seems to degrade over a period of weeks before completely breaking, and it might have been compensated for in different ways as it worsened over time. Bringing the deck to a solid, accurate state is definitely recommended.