688 won’t play

[JonHunt]

I’m repairing a tascam 688 and could use some help troubleshooting.

the deck will rewind and fast forward like normal. When you press play, nothing happens. The heads and pinch roller don’t even advance forward (they do on RW and FF). The belt is intact and moving the flywheel moves the capstan and vice versa. When you press play the flywheel does not move.

could it be the motor? Or something to do with the PCB the transport switches are connected to?

 

[JonHunt]

Update: I think it’s the switch. Pressing play during rewind or ff does not stop the transport

 

[SkywaveTDR]

The motor (capstan) should turn when a tape is in the transport. This is caused by the tape in switch on the right. There is the possibility that a tact switch could go bad. I changed a record tact switch in a 424 Mk III the other day- It worked some of the time but with a new one it worked all of the time. They are Panasonic Tactile switches and they are not being more available but less. There are a number of different kinds. Two terminal axial and 4 terminal types. You need to see if the transport is engaging and a switch contact can be soldered in parallel with the other switch- solder in with power off and then try a new tact switch- If it works then take the board off and pull that defective switch. Some switches like play and Stop fail before others. They just get used more.

 

[JonHunt]

Very good point. Also, how can I tell if it’s a motor?

 

[SkywaveTDR]

If the motor is getting power to it at the power terminals usually marked + and - then it should turn. If there is something else wrong like a crack in the Pitch control board it might not work but I have never seen that yet. Capstan motors turn as soon as they are powered and that is usually due to the cassette being in the well and pressing that skeleton switch in the upper right corner. Some third party motors can be installed to allow the deck to work but sometimes they are not exact replacements and will need some mods to get them in the right range of speed. We are dealing with old stuff that the original Japanese motor is not available and so Chinese motors

 

[JonHunt]

I resolved the tape deck issue. It ended up being a bad motor, bad pitch control PCB, and a bad switching PCB. Fortunately I had another 688 to use for parts. The only problem is now that the cue monitor won’t function during recording, only playback. But otherwise it’s fully functional.

 

[SkywaveTDR]

It is unusual for three parts to fail all at the same time unless it was abused.

 

[SkywaveTDR]

As to the block diagram the cue lines have to be selected to Group rather than tape as Tape is only suppose to go to the cue lines if set that way. When set to Group 1-8 then the signal will appear there. The Cue outs with level and pan applied on their own also can be selected at Monitor outs too.