my revox B710 mark1 cassette deck wont play record

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my beloved Revox mark1 refuses to playback or record or have any audio functions,,,,,Ive replaced most of the caps especially on the psu boards,, even replaced the ics,on audio,record playback equaliser etc...could it be on the microprocessor board? or the chip itself.... it mechanically functions well,,smooth playback ,fast forward and rw...etc except no audio....the mpx,,dolby leds light,,,as well as the record light when in record,,,theres a slight noise on left channel in source ..indicated on two bars of left channel////im near yet so far,,,in mean time ive replaced broken toggles sourced from germany,the two pinch wheels and lubed with proper german lube!the mechanics are as smoothas a nut..! can anyone help simon,,,thanks
 
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The big question is whether the deck functioned before you carried out all the work such as cap replacement and so on.

If it is mechanically OK and the tape is passing the heads correctly then finding the reason for no audio should be fairly straightforward armed with a scope and manual.

First check has to be whether ALL the supplies are correct and if so, begin by looking at the audio signal coming out the head amp section. Make sure any mute lines are at the correct logic levels.

The uP is probably the single most reliable part in there and would be the absolute last suspect normally, of course that excludes the possibility of anything untoward having happened when servicing the deck.
 
my revox B710 no playback

thank you for your quick reply....no... the deck didnt function in audio departments .. before I updated caps!i will get my scope and generator out and do some more in-depth fault finding....im pleased the microprocessor is reliable...by the way all dc outputs are there,.......,i also have revox b126 cd player with a no tray eject ,,it reads the cd and plays and cd tray goes in ok..when i try to eject nothing happens..any ideas? i updated the caps....i do check thoroughly for solder flashes or tracks breaking after i replace components!using a meter....I know pcb tracks are like tissue and require great care in soldering and desoldering...i use a proper desolder and no solder wick...i try and use minium heat in order not to lift tracks etc.. simon
 
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The CD player probably warrants a thread of its own but I would start by looking at the tray motor driver which could be discrete of an IC, but which will be configured as 'H bridge driver'. Check to see if the appropriate logic levels appear to drive the motor in either direction.

H bridge - Wikipedia

This is about as complex as these things go in CD/DVD players:

How to Build an H bridge Circuit with Transistors
 
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