sweetbeats
Reel deep thoughts...
The joint PCB scheme is on page 4-17 if the schematics. 32VDC isn't right. It's a 24V system. With the takeup tension arm raised measure for DC volts between pins 1 & 3, and then pins 1 & 4 of J2 on the joint PCB.
Tascam 388 Total Beater, looking for initial advice
- Thread starter nateflanigan
- Start date
nateflanigan
New member
Will do, my wife and I have our first child birth class tonight so I might not be able to get to it tonight. I have a few other questions about the Mecha Joint PCB schematic that may be useful for other folks down the line but I need to take some picture and put together a good post.
nateflanigan
New member
Here's some more intel...
On the Mecha Joint PCB, using the pads at the top of the board (on the right of the schematic):
With the tension arm down, 35vdc at 9, 10, 20, 21, 23, 24. IE all of the wires that connect to a motor (capstan and left and right reel) measure 35vdc to ground.
With the tension arm up, the measurements are the same.
With the tension arm up and PLAY engaged, 35vdc at 9 & 10, but all the reel motor points show a dropping reading, like a cap discharging, that drops to about 0.6vdc.
So, where does this 35v come from the Power supply board or the capstan servo board?
On the Mecha Joint PCB, using the pads at the top of the board (on the right of the schematic):
With the tension arm down, 35vdc at 9, 10, 20, 21, 23, 24. IE all of the wires that connect to a motor (capstan and left and right reel) measure 35vdc to ground.
With the tension arm up, the measurements are the same.
With the tension arm up and PLAY engaged, 35vdc at 9 & 10, but all the reel motor points show a dropping reading, like a cap discharging, that drops to about 0.6vdc.
So, where does this 35v come from the Power supply board or the capstan servo board?
nateflanigan
New member
Yet even more intel...
I figure it would be a good idea to try and check the PSU voltage as directly as possible. Since I don't have an extender card rig I read these by accessing the bottom of the Mother PCB.
P6
1) 35 vdc
P5
1) G
2) -15 vdc
3) 15 vdc
4) 16 vdc (14 vdc with play engaged)
5) 0
P7
1) 35 vdc
2) G
3) 20 vdc
4) 9.2 vdc
5) G
6) 5 vdc
Also, on the Mecha Joint PCB
Shut off points arm up
11) 1.16 vdc
12) 0.2 vdc
Shut off points arm down
11) 1.16 vdc
12) 4.21 vdc
I figure it would be a good idea to try and check the PSU voltage as directly as possible. Since I don't have an extender card rig I read these by accessing the bottom of the Mother PCB.
P6
1) 35 vdc
P5
1) G
2) -15 vdc
3) 15 vdc
4) 16 vdc (14 vdc with play engaged)
5) 0
P7
1) 35 vdc
2) G
3) 20 vdc
4) 9.2 vdc
5) G
6) 5 vdc
Also, on the Mecha Joint PCB
Shut off points arm up
11) 1.16 vdc
12) 0.2 vdc
Shut off points arm down
11) 1.16 vdc
12) 4.21 vdc
sweetbeats
Reel deep thoughts...
My mistake...the servo system on the 388 is powered by a +35VDC rail, not +24VDC. So your 32VDC and +35VDC measurements are appropriate.
As far as diagnosing what is going on all I can say is it's over my head.
As far as diagnosing what is going on all I can say is it's over my head.
jpmorris
Tape Wolf
Well, it's looking like the photointerruptor is OK, so that's something.
If the capstan motor is literally a 2-wire DC motor and not some multi-pole thing, it might be worth testing continuity on the windings. You'd have to unplug it from the deck for that, though to avoid getting false readings. Not sure what the resistance of a motor that size is likely to be, but you should get something. Might also be worth turning the motor gently while taking the measurements in case the commutator is doing something funny to the circuit in its current position.
I would have thought that if the motor's really getting the full 35V or so, it should be turning. That might indicate a problem with the motor itself, which might be fixable, e.g. a problem with the brushes. Alternatively I could be getting confused and we're still looking at a problem with the cut-out, e.g. the power transistor driving the motor has gone bad.
However, this really is guesswork, to be honest I'm out of my depth here.
OK. The motor pins appear to be 3 and 4 on the J2 connector.
Other points of interest are U809, which is the 2SC3400 switching transistor that appears to be responsible for effecting the cutoff switch. Q803, which is also associated with that, and finally Q5. Q5 is on a PCB all of its own and is marked as safety-critical so my guess is that that's the power transistor which is actually driving the capstan motor. P801 is the connector for it. Pin 2 on the 801 connector corresponds to pin 4 on J2. Pin 3 on 801 is ground.
My guess is that when the the tension arm is lifted, you should be getting something like 35V on J2-pin 4 with respect to ground. If that's not the case, it might be worth checking that you get something like that between pins 2 and 3 on the 801 connector for the power transistor.
It's late, I'm stretching my knowledge of electronics and I'm not sure if this will be coherent when I read it back in the morning, but it's the best I can do. Hope it's some use :3
If the capstan motor is literally a 2-wire DC motor and not some multi-pole thing, it might be worth testing continuity on the windings. You'd have to unplug it from the deck for that, though to avoid getting false readings. Not sure what the resistance of a motor that size is likely to be, but you should get something. Might also be worth turning the motor gently while taking the measurements in case the commutator is doing something funny to the circuit in its current position.
I would have thought that if the motor's really getting the full 35V or so, it should be turning. That might indicate a problem with the motor itself, which might be fixable, e.g. a problem with the brushes. Alternatively I could be getting confused and we're still looking at a problem with the cut-out, e.g. the power transistor driving the motor has gone bad.
However, this really is guesswork, to be honest I'm out of my depth here.
OK. The motor pins appear to be 3 and 4 on the J2 connector.
Other points of interest are U809, which is the 2SC3400 switching transistor that appears to be responsible for effecting the cutoff switch. Q803, which is also associated with that, and finally Q5. Q5 is on a PCB all of its own and is marked as safety-critical so my guess is that that's the power transistor which is actually driving the capstan motor. P801 is the connector for it. Pin 2 on the 801 connector corresponds to pin 4 on J2. Pin 3 on 801 is ground.
My guess is that when the the tension arm is lifted, you should be getting something like 35V on J2-pin 4 with respect to ground. If that's not the case, it might be worth checking that you get something like that between pins 2 and 3 on the 801 connector for the power transistor.
It's late, I'm stretching my knowledge of electronics and I'm not sure if this will be coherent when I read it back in the morning, but it's the best I can do. Hope it's some use :3
nateflanigan
New member
Yikes, if it's over the two of your heads this does not bode well for the fate of our dear 388.
Before I call it quits, there's a few threads I think I can tug on, maybe they'll reveal a path forward. Here's a few questions that perhaps either of you can shed some light on...
1) None of the motors activate, it seems more likely that there is some sort of control problem than all three motors are dead. Is it possible for either of you to write up a simple flow chart of how the transport works?
2) What does it signal to us that the left solenoid doesn't seem to work. How and when would it activate under normal circumstances?
Does anyone know of a sort of glossary of terms for the 388 specifically or even tape machines in general? It would be helpful for me if I knew what the Cap Servo Board is supposed to do.
Right now I'm very doubtful that I'll be able to get this going, I'd like to keep at it a bit, just to see if I can learn a little more. It's also very possible that even if I can get the motors spinning bigger problems might be right around the corner.
Before I call it quits, there's a few threads I think I can tug on, maybe they'll reveal a path forward. Here's a few questions that perhaps either of you can shed some light on...
1) None of the motors activate, it seems more likely that there is some sort of control problem than all three motors are dead. Is it possible for either of you to write up a simple flow chart of how the transport works?
2) What does it signal to us that the left solenoid doesn't seem to work. How and when would it activate under normal circumstances?
Does anyone know of a sort of glossary of terms for the 388 specifically or even tape machines in general? It would be helpful for me if I knew what the Cap Servo Board is supposed to do.
Right now I'm very doubtful that I'll be able to get this going, I'd like to keep at it a bit, just to see if I can learn a little more. It's also very possible that even if I can get the motors spinning bigger problems might be right around the corner.
sweetbeats
Reel deep thoughts...
Unfortunately, by this generation of equipment, Teac stopped including any "Theory of Operation" sections on their service manuals. That is what you are asking for essentially and that is also way over my head to try and interpolate the schematics and generate a diagram or document that explains how it works.
The very first thing one should ALWAYS do when troubleshooting is to make sure the power supply is producing the proper power. That means DC rails are at the correct voltage and are free of AC components, and in this case are also correct under load. This machine had problems with the interface between the power supply card and the motherboard. You have rectified that and reflowed solder joints but how do we know that improper interface didn't damage components upstream or downstream? So you need to start with the basics and make sure it's producing the correct power and can keep up with the current demand. This machine went from solenoids and reel motors doing what they were supposed to do when PLAY mode was engaged and just the capstan motor punking out, to nothing working. You are going to be chasing your tail for certain until you can first verify the power supply is doing its job.
The very first thing one should ALWAYS do when troubleshooting is to make sure the power supply is producing the proper power. That means DC rails are at the correct voltage and are free of AC components, and in this case are also correct under load. This machine had problems with the interface between the power supply card and the motherboard. You have rectified that and reflowed solder joints but how do we know that improper interface didn't damage components upstream or downstream? So you need to start with the basics and make sure it's producing the correct power and can keep up with the current demand. This machine went from solenoids and reel motors doing what they were supposed to do when PLAY mode was engaged and just the capstan motor punking out, to nothing working. You are going to be chasing your tail for certain until you can first verify the power supply is doing its job.
nateflanigan
New member
Quick update, I've been super busy this past week and I gotta pack for vacation, but I got the capstan spinning. I'll be back with a full report and some questions later next week.