ROBERTS 770X

quiet

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Hello to all. I could use a little help if you have a minute. This unit works well except.....
The switch in the picture is coming on during rewind and fast forward which reduces the speed.
The unit doesn't shut off at the end of rewind or fast forward. It does shut of at the end of play.
I see no other problems.
What is the switch for? Can someone please tell me what's going on here?
 

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SORRY! WISH I could help, but haven't a clue. FYI, My 770X motor slows from very fast to much slower during FFWD and REW as well... but at least it keep going. Not sure why. Just did a total disassemble, clean & lube of the machine - was NASTY - even huge dust bunnies inside! Works great, now except wow & flutter is pretty bad - AND - although the VU meters light up, they barely deflect. I have THREE Akai M8 tape transports coming (got them all for $30 on eBay) - hope that maybe a motor swap out will give me better results. ALSO, noted on another forum that the speed sleeve for 7 1/2 ips on the capstan is always loose on these machines creating flutter, so did what those guys suggested - super glueed it on. (I only use 7 1/2 ips anyway). Here's my machine - just posted a video for a friends birthday.
Oh, also need to tear down the reels again and replace the brake felt. I tried to "fluff it up" with a blade to increase tension, but still get tape spillage from the right reel on fast-forward. Do yours work okay? Here's my 770X SS -
- Happy Tape Fiddling! - Johnny - LongJnSilver
 
My brakes work good. I need to find out what that switch does. Did you notice where the wire from that switch goes when you had it opened up?
 
I have to remove the tape transport to get to the handle screws so will try to trace where the red and gray wires from that switch to - and get back to you.
 
The schematic shows that switch bypassing the auto shutoff switch when the unit is in 'stop' mode. It also looks like the auto stop only works in play mode as to disengage the pinch roller so it won't leave a dent in it.
The tape slowing down could be due to using a tape with sticky shed syndrome. Also a motor run capacitor that has changed value might cause that. I own several Akai/Roberts machines and most the single motor models all use a transport that is virtually the same all the way back to their first machine, the 900. I have one of those also. It would also help to take the motor completely apart and clean it and make sure the sintered bronze bearings are not glazed from the old oil breaking down. Clean them and relube them.


Dave
 
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The unit rewinds very well until I rotate the control completely into the rewind position and that switch clicks. It's a fine line between enough and to much right at the end of the control knob travel when the switch clicks. The linkage looks like that switch is supposed to be contacted during rewind.
I have 2 other Roberts that work right so I'll remove the face and watch them in action now that I know what the switch does. My attraction to this one is the twin amp tube setup
Thank you.
 
Inspect the function cam on each control shaft for swelling and cracking, if present this is crapalloy rot and is irreversible.
 
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