Thank you for such a deep dive into the AT-RMX64! I'm very thankful the finicky channel and transport issues seem fairly self-serviceable. I've been holding onto my unit hoping I could eventually hire someone to get it back to full functionality, but this looks like a worthwhile challenge. Thanks for sharing all this info.
That’s awesome…fulfills my intention with creating and posting the video. Feel free to post questions if you have them as you dig in and I’ll help as able.
Good work! Really interesting to see inside more. Those boards look to be a similar material as the cards in my tascam 122 mkii although i could be wrong. Good tips to pay attention to when looking at a unit (regarding potential corrosion).
Yeah there’s basically two types of printed circuit board base material…phenolic resin type and glass fiber type. The phenolic boards in the AT-RMX64 are extremely common, and yes they would be the same as your 122mkII. Glass fiber boards are preferable in every way AFAIC, but what’r ya gonna do…it doesn’t mean a device is “bad” or “inferior” because it has phenolic boards in it. Sometimes you’ll find a mix…my Tascam 58 1/2” 8-track has phenolic boards except for the plug-in amp cards and their motherboard. Anyway, the phenolic boards don’t make it sound any different than glass fiber. It’s just a design engineering point, and the bean-counters won with the selection of phenolic boards in the AT-RMX64.
Excellent work here! Lots of useful info and great lead on those relays! Eager to see if that gets your record issues fixed. I was working on a MT8X and there are three switch ic’s for 8 channels… same issue, no record on one channel, so a good place to look in trying to trouble shoot record issues. Looking forward to the next vid on this unit! I wonder how often a relay like the green one here malfunctions…
So what I’ve learned about the relays is they are “anti-thump” muting relays. They each have two poles. That makes six channels. I haven’t verified this but I suspect they suppress popping/thumping at the six outputs (the four SUB outs and the two auxiliary sends) at power up. There is a couple seconds when you first power the unit up where the coils aren’t energized and the contacts are open. Then the coils energize and the contacts close and stay closed the rest of the time the unit is powered. There is a 555 timer chip on the small motherboard beneath the tape section amp cards. I suspect that sets the power delay to the relays. Since all my outputs are working, I’m reasonably certain the relays are not my issue with tracks 1 & 2. Regardless, I’m going through measuring resistance across each of the six contact sets. Your comment about switching ICs got me thinking…there are 4066 chips on the SUB 1 and SUB 2 PCB assemblies but after looking at those circuits for a bit those handle the pre/post source switching for SEND 1 and SEND 2…when you actuate the push/pull RETURN 1 and RETURN 2 pots. So that’s not it. There’s another chip that was unfamiliar to me on the SUB 3 PCB assembly, a 1407, but I now know that’s the LED driver for the SOLO buss meter. I also believe the amp circuit for the SOLO buss is on the SUB 3 PCB assembly. I’m just noting some of these things as I learn them in case somebody down the road is having a problem with any of these things…might help to speed up the hunt for a solution. So anyway I don’t think Audio Technica used relays or switching ICs for mode/source switching during record and reproduce. I think they used discrete transistors. But I appreciate your suggestion a lot. I’ll take all I can get. The other thing I’m wanting to suss out is to ensure signal is getting into and out of the Dolby chips during recording. The chip used is a Hitachi HA12058NT. It’s a DIP30 part, and there’s one each on each of the SUB buss PCB assemblies, one for each corresponding tape track. I’ve not been able to find a datasheet for it…odd…and frustrating. I did find an application schematic which does help with a lot of the pinout. So I want to just verify signal bussed to each tape track is getting to each Dolby chip during record, and is also being output from the chip. I’ll have to do a little trial and error because the pinout labeling on the schematic I found isn’t totally clear which set of pins is encode and which is decode, but that should be easy to figure out. I have some ribbon cable with single pin headers at one end and single pin sockets at the other to make easy DIY extender cables. Got them off of Amazon years ago. So I’ll connect each SUB PCB to the motherboard via the extender cable and be able to probe the Dolby IC pins. I have a feeling I’ll end up needing to just trace for signal starting at the output of the record amp PCB assembly until I hit signal for tracks 1 & 2 and I’ll have the fault, but I’m doing some stabbing first based on some hypotheses in case I find the culprit that way first.
@@SweetbeatsTechStop great info here, thanks again… very much tuned into your efforts on this unit. Eager to see how the trace effort goes, that’s where I dropped off… lack of schem, extender cables, time..
Making extender cables is actually really easy and very affordable. This is what I’m using: a.co/d/89u2k7L You can see there are some different styles and lengths, but the pins and sockets fit, the 2.54mm pitch is correct…you get a set of them for $10 or $12, peel off the number you need for the given connector, remove the PCB assembly, plug pins into the motherboard and plug the sockets up to the pins on the PCB…done. Yes, it can be a little tedious since the pins and sockets are individual, but it’s a cheap readily available solution. And you could always buy header material and solder a solid piece on each end, or even possibly just superglue the individual black plastic pin and socket housings together to make a solid multi pin header. It works. And it’s cheap.
![If you can't hear this then you're not an audiophile [See description for link to followup video]](http://i.ytimg.com/vi/48PxwspDvrE/mqdefault.jpg)
![If you can't hear this then you're not an audiophile [See description for link to followup video]](/img/tr.png)
Thank you for such a deep dive into the AT-RMX64! I'm very thankful the finicky channel and transport issues seem fairly self-serviceable. I've been holding onto my unit hoping I could eventually hire someone to get it back to full functionality, but this looks like a worthwhile challenge. Thanks for sharing all this info.
That’s awesome…fulfills my intention with creating and posting the video. Feel free to post questions if you have them as you dig in and I’ll help as able.
Good work! Really interesting to see inside more. Those boards look to be a similar material as the cards in my tascam 122 mkii although i could be wrong. Good tips to pay attention to when looking at a unit (regarding potential corrosion).
Yeah there’s basically two types of printed circuit board base material…phenolic resin type and glass fiber type. The phenolic boards in the AT-RMX64 are extremely common, and yes they would be the same as your 122mkII. Glass fiber boards are preferable in every way AFAIC, but what’r ya gonna do…it doesn’t mean a device is “bad” or “inferior” because it has phenolic boards in it. Sometimes you’ll find a mix…my Tascam 58 1/2” 8-track has phenolic boards except for the plug-in amp cards and their motherboard. Anyway, the phenolic boards don’t make it sound any different than glass fiber. It’s just a design engineering point, and the bean-counters won with the selection of phenolic boards in the AT-RMX64.
Excellent work here! Lots of useful info and great lead on those relays! Eager to see if that gets your record issues fixed. I was working on a MT8X and there are three switch ic’s for 8 channels… same issue, no record on one channel, so a good place to look in trying to trouble shoot record issues.
Looking forward to the next vid on this unit!
I wonder how often a relay like the green one here malfunctions…
So what I’ve learned about the relays is they are “anti-thump” muting relays. They each have two poles. That makes six channels. I haven’t verified this but I suspect they suppress popping/thumping at the six outputs (the four SUB outs and the two auxiliary sends) at power up. There is a couple seconds when you first power the unit up where the coils aren’t energized and the contacts are open. Then the coils energize and the contacts close and stay closed the rest of the time the unit is powered. There is a 555 timer chip on the small motherboard beneath the tape section amp cards. I suspect that sets the power delay to the relays. Since all my outputs are working, I’m reasonably certain the relays are not my issue with tracks 1 & 2. Regardless, I’m going through measuring resistance across each of the six contact sets.
Your comment about switching ICs got me thinking…there are 4066 chips on the SUB 1 and SUB 2 PCB assemblies but after looking at those circuits for a bit those handle the pre/post source switching for SEND 1 and SEND 2…when you actuate the push/pull RETURN 1 and RETURN 2 pots. So that’s not it. There’s another chip that was unfamiliar to me on the SUB 3 PCB assembly, a 1407, but I now know that’s the LED driver for the SOLO buss meter. I also believe the amp circuit for the SOLO buss is on the SUB 3 PCB assembly. I’m just noting some of these things as I learn them in case somebody down the road is having a problem with any of these things…might help to speed up the hunt for a solution. So anyway I don’t think Audio Technica used relays or switching ICs for mode/source switching during record and reproduce. I think they used discrete transistors. But I appreciate your suggestion a lot. I’ll take all I can get. The other thing I’m wanting to suss out is to ensure signal is getting into and out of the Dolby chips during recording. The chip used is a Hitachi HA12058NT. It’s a DIP30 part, and there’s one each on each of the SUB buss PCB assemblies, one for each corresponding tape track. I’ve not been able to find a datasheet for it…odd…and frustrating. I did find an application schematic which does help with a lot of the pinout. So I want to just verify signal bussed to each tape track is getting to each Dolby chip during record, and is also being output from the chip. I’ll have to do a little trial and error because the pinout labeling on the schematic I found isn’t totally clear which set of pins is encode and which is decode, but that should be easy to figure out. I have some ribbon cable with single pin headers at one end and single pin sockets at the other to make easy DIY extender cables. Got them off of Amazon years ago. So I’ll connect each SUB PCB to the motherboard via the extender cable and be able to probe the Dolby IC pins.
I have a feeling I’ll end up needing to just trace for signal starting at the output of the record amp PCB assembly until I hit signal for tracks 1 & 2 and I’ll have the fault, but I’m doing some stabbing first based on some hypotheses in case I find the culprit that way first.
@@SweetbeatsTechStop great info here, thanks again… very much tuned into your efforts on this unit. Eager to see how the trace effort goes, that’s where I dropped off… lack of schem, extender cables, time..
Making extender cables is actually really easy and very affordable. This is what I’m using: a.co/d/89u2k7L
You can see there are some different styles and lengths, but the pins and sockets fit, the 2.54mm pitch is correct…you get a set of them for $10 or $12, peel off the number you need for the given connector, remove the PCB assembly, plug pins into the motherboard and plug the sockets up to the pins on the PCB…done. Yes, it can be a little tedious since the pins and sockets are individual, but it’s a cheap readily available solution. And you could always buy header material and solder a solid piece on each end, or even possibly just superglue the individual black plastic pin and socket housings together to make a solid multi pin header. It works. And it’s cheap.