Author Topic: Revox B77 Record switch repair  (Read 1966 times)

Offline mygoggie

Re: Revox B77 Record switch repair
« Reply #45 on: November 29, 2019, 01:32:16 PM »
There is no timing system in the PROM itself.
It acts as an "algorithmic state machine" (ASM): it just jumps immediately from one logic state (defined by certain output bits) to another, depending on the input bits.
One of those input bits is the tape motion sensing circuit, which outwardly can seem like a delay, but it is simply the ASM going into an "alternate stop" state while the tape motion sensor declares the tape to be in a non-stationary condition.

The high start torque on the take up reel is performed "after" the PROM state selection of Play mode, by the NAND gate and C7.

@Steerpike is correct. I looked at the programming datasheet for this chippy and the timing is controlled by a capacitor.
Herman

~ To heal the soul is to embark on a new journey. ~

Offline mygoggie

Re: Revox B77 Record switch repair
« Reply #46 on: November 29, 2019, 01:33:27 PM »
Nothing much really, its mostly hobby use, lathe is a Winchester - Imperial leadscrew but cuts metric perfectly,

Very nice setup. I run a Colchester Student. One day when I am a grown up I will get me a mill as well ...  :sd:
Herman

~ To heal the soul is to embark on a new journey. ~

Offline marcochezzi

Re: Revox B77 Record switch repair
« Reply #47 on: November 29, 2019, 01:45:30 PM »
There is no timing system in the PROM itself.
It acts as an "algorithmic state machine" (ASM): it just jumps immediately from one logic state (defined by certain output bits) to another, depending on the input bits.
One of those input bits is the tape motion sensing circuit, which outwardly can seem like a delay, but it is simply the ASM going into an "alternate stop" state while the tape motion sensor declares the tape to be in a non-stationary condition.

The high start torque on the take up reel is performed "after" the PROM state selection of Play mode, by the NAND gate and C7.

aaah, gotcha, thank you Steerpike, that paints a completely different picture in my mind, that's brilliant, thank you thank you..!!

Offline marcochezzi

Re: Revox B77 Record switch repair
« Reply #48 on: November 29, 2019, 01:51:02 PM »
Very nice setup. I run a Colchester Student. One day when I am a grown up I will get me a mill as well ...  :sd:

Nice, very nice, I always wanted a Colchester Student, built like a proverbial concrete bomb shelter, by the time I finally found one I already had what I had, and since as a general rule I always lose money selling anything I own, I opted to keep her... But one day, she will have a senior, this I promise you, its just getting her past SWAMBO that could throw the cat amongst the pigeons.. :giggle:

Offline mygoggie

Re: Revox B77 Record switch repair
« Reply #49 on: November 29, 2019, 02:56:24 PM »
its just getting her past SWAMBO that could throw the cat amongst the pigeons.. :giggle:

Nothing like turning her a fancy chandelier ... or a bracelet ... or a nose ring ... you know what I mean  :cleansound:
Herman

~ To heal the soul is to embark on a new journey. ~

Offline fdlsys

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Re: Revox B77 Record switch repair
« Reply #50 on: November 29, 2019, 04:03:44 PM »


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Offline FranZAR

Re: Revox B77 Record switch repair
« Reply #51 on: November 29, 2019, 04:42:25 PM »


...from FDLSYSY...

Grumpy and a sysy .


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Offline mygoggie

Re: Revox B77 Record switch repair
« Reply #52 on: November 30, 2019, 06:45:03 AM »
@marcochezzi I have asked in a few groups on the www for a chippy, software or logic diagram. Let's see what pops up!
Herman

~ To heal the soul is to embark on a new journey. ~

Offline mygoggie

Re: Revox B77 Record switch repair
« Reply #53 on: November 30, 2019, 06:55:28 AM »
@marcochezzi I found you a chippy and a lot of new repair spares

https://nagravox.com/collections/revox-b77/products/controller-ic-for-all-revox-b77-and-pr99-includes-new-socket   <-- AUZ$56

Interesting comment they make - This IC often becomes faulty as a result of capacitor degradation with age.  A recap of PSU motors and tape transport modules should be done before replacing this IC. One of our electronic kits is highly recommended.

I would buy this chippy and what else you need and have someone coming SA's way from Auz just bring it with. There are many people going back and forth this Christmas season.
« Last Edit: November 30, 2019, 06:58:53 AM by mygoggie »
Herman

~ To heal the soul is to embark on a new journey. ~

Offline mygoggie

Re: Revox B77 Record switch repair
« Reply #54 on: November 30, 2019, 09:24:04 AM »
Herman

~ To heal the soul is to embark on a new journey. ~

Offline marcochezzi

Re: Revox B77 Record switch repair
« Reply #55 on: November 30, 2019, 07:06:55 PM »
@marcochezzi I found you a chippy and a lot of new repair spares

https://nagravox.com/collections/revox-b77/products/controller-ic-for-all-revox-b77-and-pr99-includes-new-socket   <-- AUZ$56

Interesting comment they make - This IC often becomes faulty as a result of capacitor degradation with age.  A recap of PSU motors and tape transport modules should be done before replacing this IC. One of our electronic kits is highly recommended.

I would buy this chippy and what else you need and have someone coming SA's way from Auz just bring it with. There are many people going back and forth this Christmas season.

Thank you Mygoggie, yes I cam across Nagravox last week via Studer users page on Facebook, sadly they did not get a good review, however itís a blessed chip, hardly a moving part so yes, I will consider that in the next few days... Appreciate your time captain!!  :dop:

Offline Jaxxon

Re: Revox B77 Record switch repair
« Reply #56 on: December 03, 2019, 05:59:07 PM »
Sincere thanks Marco for your offer.

I will take you up on it.

With Christmas around the corner, I will wait until the new year before sending it.

I pack well, so there should be no damage.

If you will PM me your address, I will get things moving.

Regards

Jaxx

Offline marcochezzi

Re: Revox B77 Record switch repair
« Reply #57 on: December 04, 2019, 11:56:10 AM »
Sincere thanks Marco for your offer.

I will take you up on it.

With Christmas around the corner, I will wait until the new year before sending it.

I pack well, so there should be no damage.

If you will PM me your address, I will get things moving.

PM sent..

Regards

Jaxx