Tascam 244 transport motor not working

[gbkd80]

Just need to be pointed in the right direction on this one:

Fired up my 244 the other day. It's been sitting at least a year. Transport/head assembly engaged once, then it stopped, killed the tape. Had to manually disengage it. Belt is a little stretched from sitting but not bad (it had been replaced already). The actual problem is, the control motor itself does not move. I thought it was supposed to engage at power up, or at the very least by control (play/stop etc). I put a 9v on the motor and the motor is working, so it's not the motor itself. I also tested both large caps on the Drive PCB assembly (the board with the motors within the top of the transport assembly) and both tested fine but I replaced the 1000uf since I had them, and I'd still need a 10000uf low-profile cap to do the other - but again it seemed to test fine.

I have the service manual, and I've been studying Control Assembly B where U501 and U509 play a part in the motor engaging (or so it sounds by the circuit description).

Anyone have any insight to offer on this, that's seen the actual problem where it's not a belt and the motor actually isn't engaging?

 

[gbkd80]

Figured it out.

Big crack in the ground plane on the Drive PCB:


Made a little makeshift bridge to fix the crack. Back in bidness...

 

[-mjk-]

Yeah, I'd say! Might want to drill a small hole at the end to contain the crack. I might be also inclined to coat it with epoxy.

 

[gbkd80]

The epoxy will definitely be done. I just wanted to test and make sure it was actually the problem.

Explain what you mean by drill a small hole to contain the crack. Through the crack?

 

[Arjan P]

If you drill a small hole right at the end of the crack, it usually remains the end of the crack. Otherwise chances are it will continue to grow (especially in a moving/vibrating environment).

You might also wanna check the tension to the PCB that may be created by the fasteners (screws)..

 

[-mjk-]

The epoxy will definitely be done. I just wanted to test and make sure it was actually the problem.

Explain what you mean by drill a small hole to contain the crack. Through the crack?

Sure. It's an old machinist's trick to strain relieve a crack. Somehow, you have to stop the crack from propagating further, and one way to do that is to drill a hole at the very end of the crack. The crack tends to not propagate through the free space created by the hole.

 

[-mjk-]

@Arjan P you nailed the explanation.

You might also wanna check the tension to the PCB that may be created by the fasteners (screws)..

Excellent suggestion!

 

[gbkd80]

Oh yeah, I've taken the board off and replaced the 1000uf cap while it was out, so I already know it wasn't tensioned in any way that would cause the crack, but when I got it you could tell it had been neglected so it wouldn't surprise me if it fell off a table or something at some point...

I'll be pulling out the cards and re-capping them along with the power supply soon. Any of you guys re-capped a 244 in its entirety? Necessary to do all the boards? I get pretty cap-happy when i do replacements so I'm figuring I'll be doing everything, but if it's not in the audio path I wonder if it matters (aside from there being a known problem associated with it).

 

[-mjk-]

@gbkd80 I've recapped several large-format recording consoles back in the day. When one electrolytic dries out, the rest are basically in the same condition so, if you're gonna do one you should do them all. The last thing you want to do is open it up next year to do the rest of the caps.

Some console designs use electrolytic caps in the audio path where there is no polarizing voltage for them. We found that in those cases, replacing them with a non-polar electrolytic and a small film capacitor tacked across the leads creates a mini crossover that eliminates most of the mid range smear. In those types of jobs, I always recommend doing the monitor section 1st so you can hear the difference as you go along.