Please help with ReVox A77 MKIV restoration project.

[~poorcow]

hi everyone,

i am writing from London, UK.

i just got a non-functioning A77 MKIV as a restoration project.

the dummy pluh is present. the machine powers up OK. but the capstan motor is not running and the end of tape lamp does not come on. when all the buttons (Play/Rec/FF/RW/Stop) pushed they engaged with no problems, the reels motors run as they should. what should i look into to start with? my first instinct tells me to poke at the motor run capacitor, but how does that cap affects the end of tape lamp?

i can confirm that the capstan motor is NOT faulty as i hook it up to my other working A77 and it spins as soon as i turn the power switch.

anybody knows why the Rec head has Green paint dot and the Playback head has RED paint dot and not the other way round?

are the Rec and Playback boards for 2-track and 4-Track the same and are interchangeable? what about the oscillator board?

thanks in advance for your input.

[andreas42]

Hi poorcow,

are the Rec and Playback boards for 2-track and 4-Track the same and are interchangeable? what about the oscillator board?

the oscillator board is different between 2- and 4-track, but the other amplifiers should be the same, as far as I remember. You can verify this in the service manual, which you can download there:

ftp://ftp.studer.ch/Public/Products/Revo...7_Serv.pdf

I leave the other issues for someone to comment who knows better than me...

Cheers,
Andreas

Edit: spelling

[user-332]

Hi poorcow,

your problem may be due to missing stabilised 21V. If the bulp itself is o.k., check this voltage.

The cause may be (if it's missing or low leveled) a shorted condenser, for example C306 on the 'mainboard'. But other candidates pending... Are audio electronics working (input section)?

The red/green coloration has it's tradition at Studer, see the actual auctions at the well known powerhouse . I just don't know, what is the reason for this color selection, but we will ask Guido Besimo at our meeting in autumn/fall.

Good luck with your A-77.

[~poorcow]

thank you so much for your input!

i just checked and C307 is fine but C306 is indeed short circuited. i will replace it and report back.

regarding the color coding of the heads, i just automatically think that red is always for RECORD, but i know to confirm them i should check the part number (22/27/42/47).

thanks again and i will be back for more question!!

cheers,
poorcow.