Audio Technica AT-RMX64 (cassette 4-track) repair story

famous beagle

Well-known member
Hey everyone, for those interested:

As I mentioned in another thread, I picked up an alleged fully-functional AT-RMX64 4-track in all original packaging for $65 off Craigslist. When I met with him to pick it up, he already had it packed up, and I had my 3 year old son with me, so I didn't have time to ask him to unpack it and hook it back up for a test drive. (And he didn't live too far from me ... and I obviously knew now where he lived.) :)

When I got it home and turned it on, the first thing issue was that the bulbs in the VU meters 1 and 2 were out. Not a deal-breaker I thought, because I knew those could be replaced.

Then I put a tape in and pressed play: all good. When I pressed rewind though, it tried for a few seconds, the tape didn't move, and then it stopped. I pressed FF, and it started to move sluggishly. After a few seconds, it began to pick up speed and was soon off to the races. I let it run the length of the tape (a 90 minute), thinking that maybe it was good to be "stretching its legs," so to speak. Once it hit the end, I hit RW, and low and behold, it worked. It rewound the whole tape without a problem. I then began testing the recording functions on each track, EQ, and the input channels with a 57 (and then with an Oktava MC 012---the AT has phantom power!), and everything worked flawlessly. The transport continued to work without any trouble this whole time (including the return-to-zero function).

That was all I had time for that day. The next day, I fired it up again, and again the RW function wouldn't work at first. I played the tape for a bit, then FF for about 10 seconds. I then hit RW, and it was sluggish at first. Soon, it hit full stride and, again, I didn't have any problems with the transport for the remainder of that session.

So ... my question for the porta-experts is this: Is this a sign of impending death for the transport? Or could it theoretically continue working this way indefinitely? If it stays like this, I can live with it. It's still usable. It's just that it seems to take a few minutes of warm up before it hits full stride. But if this is a sign of its last legs, I'm a little concerned because of the scarcity of these machines (and therefore the parts).

On another note, I decided to document the repair of the VU bulbs in the hopes of saving someone else some time should they ever have the same problem.

Step 1: Unplug power cord from wall (obviously).

Step 2: Remove front panel screws. There are 16 of them, and they're circled in photo 01.

Step 3: Remove the three screws holding the meter bridge cover on (circled in photos 03 and 04)

Continued
 

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Step 4: Remove meter bridge case and flip it over (photo 05)

Step 5: Remove meter bridge PCB from casing by removing three screws, shown in photos 06-09.

Continued
 

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Step 6: There are only pieces of tape holding each plastic meter case on: a reflective strip that goes all across the bottom (you can see these in photo 09) and a piece of scotch tape on the top (photo 10). You can peel these off or just slice them with an exacto knife and retape them with a new piece when you're done (which is what I did).

Step 7: Remove the plastic casing (photo 11) and snip out the old bulb (photo 12). Alternatively, you could heat the solder, remove it with a solder sucker, and then just pull the old bulb out with some needle nose pliers.

Step 8: Hook up the new bulb using alligator clip test leads just to make sure it works. (I did this and thought I took a picture of it, but now I can't find it.)

Step 8: If you haven't removed the old solder and wire ends (if you clipped out the old bulb), do so now.

Step 9: Solder the new bulb into place and clip off excess leads. Power on the machine (being careful to not touch any internal components and make sure the bulb works (photo 13).

That's it! Repeat steps 7-9 for any additional bulbs that are burnt out.

Interestingly, when I replaced the first bulb, it burned a bit brighter than ch. 3 and 4. I thought it was because my new bulbs weren't frosted and the old ones are. But I went ahead and replaced all 4 bulbs because I figured if CH. 1 and 2 were out, the other two were soon to follow. But CH. 1 and 2 still burned a bit brighter. Who knows?
 

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  • 13 New bulb soldered and working.JPG
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Looks nice! :)

About the transport rewind issue, I'd suspect a rubber edged cam drive wheel or drive belt that's marginal. You might try cleaning the rubber with some Caig RBR rubber cleaner, which might improve the grip by softening the rubber surface a bit. I don't know what parts availability would be like but I'd suspect it would be a real hunt to find original parts. You might get lucky and find a TASCAM part that would fit but you'd need to know the exact specs of each to do that.

Cheers! :)
 
Hot damn! This is why I f-ing love this place! I found another thread here describing a similar problem to mine (sluggish FF and RW), and he solved it by removing the idler tire, cleaning it, and sanding off the shiny, hardened surface with some 1000 grit sandpaper. So I tried the same thing---it took literally all of 5 minutes---and BAM! Perfect RW, perfect FF. This thing is working like new! And I got it for $65!!!! :) I'd really like to know what they retailed for in 1985.

I'm a happy camper today.
 
I bet that 1000-grit guy was me! I believe these were something like $3k when they were introduced.

I haven't worked on mine in quite a while, until I recently decided I needed to finish up this project. My playback is still really warbly but it all seems to work for the most part. Any ideas on fixing the warble?
 
I bet that 1000-grit guy was me! I believe these were something like $3k when they were introduced.

I haven't worked on mine in quite a while, until I recently decided I needed to finish up this project. My playback is still really warbly but it all seems to work for the most part. Any ideas on fixing the warble?

Hey, then thanks for your post back then! :)

By "warbly," do you mean in terms of playback speed or audio clarity?
 
I just picked one up in really nice condition . Works perfectly except 1 bulb is out on meter 3 . I did some online research and read that brand new in 1985 they retailed for $ 1500. I would like to know what the value of one of these is today. From what I have seen online , the prices are all over the place . From $ 5 to $ 400. $5 !!! Give me a break !! In the condition of mine , I would say that $ 300 is more like it . These were top of the line recorders in their day , and many are still used today with great results. There is something special about old school recording . You just can't get the same sound digitally that you can with this cassette recorder . Look , I love cds and the great sound quality but I still love cassettes . I have boxes of them , most from the 80s , and on my jvc cassette player , they still sound great !!
 
Awesome find! Best of luck with it. It's truly an awesome machine. The only 4-track cassette recorder I ever saw with phantom power on the XLR jacks. (There may have been others, but I never saw one.) Unfortunately, I had to get rid of mine a few years ago because I discovered other issues that were beyond my skill level for repair. I replaced it with another 4-track heavyweight - the Tascam 246. :)

I really wanted that AT machine to work out because it's just one of the coolest-looking and most feature-filled 4-track cassette machines out there. And talk about built like a tank - 51 pounds! :eek:
 
Hey everyone, in a desperate attempt for some help I'm trying to revive this old thread. I USED to have a very solid RMX64 but as of recently the transport starting taking a while to come to life. Last time I turned it on it took nearly all day of it being on for the transport to light up and function. I turned it on a couple of days ago and it still hasn't come to life. I think she might need some help. Any ideas what could be causing this?

Apart from that all the other transport controls worked really great once it came on.
 
First place I’d look is the power supply for the transport. I don’t know if it’s 24V or 12V or something else on that unit…don’t have a service manual for that one…hen’s teeth it is unfortunately. But maybe there is a failure in the transport power supply or a bad connection along the way, high resistance that reduces as things warm up, but step 1 IMO would be to isolate the transport power supply and make sure it’s producing clean power of the right voltage, and then do a load test and see how much oomph it has. In the meantime you can visually inspect and exercise any interconnections you see along the way to see if you an identify or resolve a fault, but any of this is going to be tough without a service manual.

AT-RMX64 is a super cool device though.
 
Just heard back from a tech in the area and sadly he is giving up on trying to figure out the issue. He is pretty confident that its a power issue but cant seem to track down the specific issue.

Anyone have recommendations on next steps? Or know of a good tech? Im in Southern California
 
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