REVOX A700! It's 'smoking!'

[pqlia]

Hey all!

I've been given a Revox A700, was disappointed as it didn't work at first due to what I thought were rusty heads, i left it for a few days and then realised that the 'rust' was actually oxide. After cleaning them i tried a test recording and couldn't really believe what I heard! I was expecting narrow bandwidth, noise, wow/flutter, drop outs etc etc. Instead I heard an amazing sound - clean, big, 'warm,' robust, dense when driven etc etc.. it really didn't sound like I expected a machine from 1974 to sound!

:tears: :sigh: Now for the tears and sadness - I attempted to record my first backing vocals using the A700 that was destined to be dubbed to PC as part of a musical arrangement and POOOOF!!! I turned to see my house full of smoke that was escaping through the tape head chassis. VERY disappointed!

I have absolutely no clue about electronics really - I read a post somewhere which said don't attempt to plug in a machine from that age without first checking the caps and some key components. I'm wondering what those KEY COMPONENTS might be?

Can anyone advise me where to start looking - my plan is simply to dismantle it and look for obvious signs of component failure, then hopefully replace that part. Is that a good plan?

Thanks

 

[david winter]

Could be many things. Of the most common:
- Shorted motor capacitors. These are screwed to the chassis, there are three of them: one for the left reel, one for the right reel, and one for the capstan.
- Shorted 0.47 capacitors (soldered on the pcb with a 47 ohms resistor in series, which burns when the cap shorts). There are three of these too. They are usually rated under 250V and are translucid.
- Shorted electrolytic capacitor, but this wouldn't generate that much smoke.
- Shorted winding in the mains transformer. Never seen this but could happen if your machine has been stored in a humid area (hence the rust) causing significant humidity to get into the transformer.

You should either find someone who's reputable in fixing these machines, or just find another one. The 700 is interesting for playing at 15ips, 7.5ips and 3.75ips. But if you only want 15/7.5 get a PR99 or a B77 and make sure the heads aren't worn. They are expensive.

 

[pqlia]

Could be many things. Of the most common:
- Shorted motor capacitors. These are screwed to the chassis, there are three of them: one for the left reel, one for the right reel, and one for the capstan.
- Shorted 0.47 capacitors (soldered on the pcb with a 47 ohms resistor in series, which burns when the cap shorts). There are three of these too. They are usually rated under 250V and are translucid.
- Shorted electrolytic capacitor, but this wouldn't generate that much smoke.
- Shorted winding in the mains transformer. Never seen this but could happen if your machine has been stored in a humid area (hence the rust) causing significant humidity to get into the transformer.

You should either find someone who's reputable in fixing these machines, or just find another one. The 700 is interesting for playing at 15ips, 7.5ips and 3.75ips. But if you only want 15/7.5 get a PR99 or a B77 and make sure the heads aren't worn. They are expensive.

Thanks so much for your response. I'm getting an electrician to call round and have a look at it. Your info regarding the location of possible component failures will come in very useful, i only hope its something that is easy to repair!

The machine was stored for years in an office store room - it was to be expected that something may go wrong. You suggest finding another - i've had a look around with no success. It was nice to have one given to me but i'm thinking now that i wouldnt really buy another if it wasnt ridiculously cheap!

Regards

 

[Negotiableterms]

Wow... I really hope you get it up and running.

When the A700 came out it was a thing of wonder. Full logic controls, three speeds, and beautiful. I lusted after one for years, but by the time I could afford a used one, the parts were so scarce and the remaining life too short... aging sucks, methinks.

 

[pqlia]

Wow... I really hope you get it up and running.

When the A700 came out it was a thing of wonder. Full logic controls, three speeds, and beautiful. I lusted after one for years, but by the time I could afford a used one, the parts were so scarce and the remaining life too short... aging sucks, methinks.

I really hope i getting it up and running too! The recordings i did before the cloud of smoke were amazing! i really was shocked! didnt expect 1974 technology to sound so clean and accurate and as you say, it is a thing beauty!

thanks for your interest, I'll let you know what happens.

 

[Tinman]

I own 2 A700's. They aren't hard to fix if you understand them. PLEASE don't let a hack touch that deck! The A700 is pretty unique in it's construction, so it requires a revox guy to fix right.

Most likely it smoked one of the 0.47 caps, the little translucent rectangular one's.
It could also be one of the gold colored FRAKO caps. Anyway, the machine is well worth fixing. The A700 is a collectors item. Again, be careful who you let touch it.
There are a few IC's in it that are no longer available, others can be subbed if you know what you are doing. Experience is key here.

If you want help, PM me.

Marc

 

[pqlia]

I own 2 A700's. They aren't hard to fix if you understand them. PLEASE don't let a hack touch that deck! The A700 is pretty unique in it's construction, so it requires a revox guy to fix right.

Most likely it smoked one of the 0.47 caps, the little translucent rectangular one's.
It could also be one of the gold colored FRAKO caps. Anyway, the machine is well worth fixing. The A700 is a collectors item. Again, be careful who you let touch it.
There are a few IC's in it that are no longer available, others can be subbed if you know what you are doing. Experience is key here.

If you want help, PM me.

Marc

Thanks so much Marc for your help. You are obviously very knowledgable on this machine. Now I'm in two minds whether or not to get a general electrician to open it up and have a look after reading your post.

You live such a long way away, it's a shame you're not closer as i'd be on your doorstep asking for help to repair it.

Anyone out there who can point me in the direction of a fairly priced and reputable Revox service man in or close to Nottingham England? It's presently sitting looking pretty but non-functioning which is a shame. It powers up and the transport still works but refuses to make a sound which is a shame because what a beautiful sound that was!!

 

[mashaffer]

Why don't you open it up carefully and take some pics for posting? Maybe the Tinman can help determine where you stand from that. With all of that smoke something ought to be obvious.

mike

 

[pqlia]

Why don't you open it up carefully and take some pics for posting? Maybe the Tinman can help determine where you stand from that. With all of that smoke something ought to be obvious.

mike

Talk about the obvious! That's a very very good suggestion which i'd not even thought of. (i'm getting old!)

Just noticed from the worn screw heads that someone must have been inside it many times in a previous life.

I will do just that. Thanks for your very sensible suggestion. I only joined this forum as a result of this Revox fault and am very impressed with the helpfulness of the posts.

Again, many thanks. Pics will follow shortly.

 

[SaSi]

And don't let anyone that don't know what they are doing to open up and touch the deck. An electrician certainly doesn't know his way around a tape deck.

Get the service and operation manual from here , study the disassembly instructions while you remove screws and panels and take plenty of pictures as you proceed. If it's your first time don't rush things.

And if something doesn't want to come off, don't force it. Take pics and post them with questions.

I don't have an A700 - wish I had - but do have some lesser Revox PR99 decks. They sound awsome, which says a lot about what a performer the A700 is.

 

[pqlia]

And don't let anyone that don't know what they are doing to open up and touch the deck. An electrician certainly doesn't know his way around a tape deck.

Get the service and operation manual from here , study the disassembly instructions while you remove screws and panels and take plenty of pictures as you proceed. If it's your first time don't rush things.

And if something doesn't want to come off, don't force it. Take pics and post them with questions.

I don't have an A700 - wish I had - but do have some lesser Revox PR99 decks. They sound awsome, which says a lot about what a performer the A700 is.

It gets better and better all this advice! Thank you SaSi! I feel i have so much more knowledge now to help me when i open up the A700, almost everytime i post i have to comment on how amazing this thing sounded after sitting in an office store room for years! I have a 96k computer recording system in my home studio and the Revox A700 sat there proudly looking into the 'face' of the computer as if to say, 'if that's all you have to offer...bring it on!' I only hope the end of this story doesnt end it tears:tears:

I will proceed with the utmost care and caution.

Thanks once again. Pics will follow shortly.

 

[peteruk]

Revox A700, Its smoking.

Hello PQLIA

http://www.taperecorder.co.uk[/url] They specialise in Revox and Studer M/cs.And have spares etc
They are based in Ipswich so aren't that far away from you. Little trip down the M11.
You could phone for advice probably.
I have no idea of cost though.
Hope this helps.
Keep the electrician away from your Revox though !. He wont have a clue...
Regards PeterUK.

 

[jan_stevns]

...... I only hope the end of this story doesnt end it tears:tears:

This story would of course end happy ! Your deck will behave and stop smoking once the cause is found and cured.

until then, take a look here : http://www.reeltoreel.de/worldwide/A700.htm

As someone else mentioned - there are some big capacitors in the Revox decks, that have a habbit of getting bad, them frako's are quite often the culprit's ..

And yes - a deck from 74' - can sound really good - the a700 is said to be the home version of a Studer A810 - which is a fantastic deck

 

[Tinman]

And yes - a deck from 74' - can sound really good - the a700 is said to be the home version of a Studer A810 - which is a fantastic deck

And having both, I can agree with that. Although the A810 is miles ahead of the A700 in so far as it's computer controlled.

Anyway, it may be possible to diagnose it remotely, taking some pictures. These decks are fairly modular, so in a pinch a board can be mailed for service, etc.

Marc

 

[Cogsinister]

Its a bit north of you bur i here this guy is very good.

http://www.revox.freeuk.com/

Cheadle Cheshire.....worth a day out maybe......

 

[pqlia]

Hello PQLIA

http://www.taperecorder.co.uk[/url] They specialise in Revox and Studer M/cs.And have spares etc
They are based in Ipswich so aren't that far away from you. Little trip down the M11.
You could phone for advice probably.
I have no idea of cost though.
Hope this helps.
Keep the electrician away from your Revox though !. He wont have a clue...
Regards PeterUK.

Thanks Peter

That is a great site! I'm a little financially challenged so i'll proceed with caution to have a peep inside the unit first and see how far i get. I think i'll have time today to investigate and post up some pics hopefully of the smoking culprit

Regards.

Baz

 

[pqlia]

This story would of course end happy ! Your deck will behave and stop smoking once the cause is found and cured.

until then, take a look here : http://www.reeltoreel.de/worldwide/A700.htm

As someone else mentioned - there are some big capacitors in the Revox decks, that have a habbit of getting bad, them frako's are quite often the culprit's ..

And yes - a deck from 74' - can sound really good - the a700 is said to be the home version of a Studer A810 - which is a fantastic deck

Thanks for the link, some great info! I actually did a search and found some red herrings and a manual download site (at least i thought) that kindly proceeded to download a trojan to my laptop and nearly wiped it out! At least now i have two or three authentic very good sources of info.

Regards

 

[pqlia]

And having both, I can agree with that. Although the A810 is miles ahead of the A700 in so far as it's computer controlled.

Anyway, it may be possible to diagnose it remotely, taking some pictures. These decks are fairly modular, so in a pinch a board can be mailed for service, etc.

Marc

Hi Tinman

Thanks so much for agreeing to give my REVOX A700 a look-over. I haven't yet plucked up the nerve to completely dismantle the unit. I think I may potentially do it more damage as I'm quite a novice in my understanding of these machines.

I searched around and can see no major aftermaths of explosions! However i saw what seemed to me to be a burned out component (see attached images for close-up and location)

I don't actually know if it was this component which caused the smoke? It seems quite small to generate a fair amount of smoke? (From memory, the amount of smoke escaping from the machine was equivalent to setting alight an A4 sized piece of paper) Due to my limited knowledge of electronics, I cannot tell you what this component is, maybe a capacitor or resistor? There is an array of identical components on the board. The components have a translucent, amber and wax coloured wax-like substance inside a clear membrane. It looks as though this substance has cracked but I don't know whether or not this is the usual appearance of these components. Certainly the bottom right-hand component (as shown in the close-up) has completely cracked open.

I did cautiously test the until after the burnout (with one hand ready on the power off!) and the mechanism still seemed to function ok. But the unit wasn't producing any sound – is this burned out component responsible in anyway for the audio output of the device?

Please let me know if you require any further information or images.

Thanks in anticipation for your help.

 

[SaSi]

...Most likely it smoked one of the 0.47 caps, the little translucent rectangular one's.
It could also be one of the gold colored FRAKO caps. ...
Marc

He didn't really need pics to diagnose the fault. :tresbon:

Since Marc mentioned the gold frakos, it's worth to look at them as well.

Now, I don't know my way around an A700 but it looks like a burnt capacitor on a power distribution board. Could be this cut power to the audio circuits.
Anyway, don't panic and feel happy. The fault is one of the simplest ones to cure. That's how I got me a cheap B795 turntable...

 

[pqlia]

He didn't really need pics to diagnose the fault. :tresbon:

Since Marc mentioned the gold frakos, it's worth to look at them as well.

Now, I don't know my way around an A700 but it looks like a burnt capacitor on a power distribution board. Could be this cut power to the audio circuits.
Anyway, don't panic and feel happy. The fault is one of the simplest ones to cure. That's how I got me a cheap B795 turntable...

Thankyou, thankyou, thankyou!

:thmbsp: my face is nearly smiling! and my ears longing for the sound of music

Regards

Thanks for confirming that component was one (hopefully the only one) of the smoking culprits! Because all this Frako speak is new to me I read Tinmans post but didn't make the connection that he was indeed referring to one of these translucent capacitors.

My course of action now is to contact the service people which posters have kindly made me aware of, find out the cost of the aforementioned capacitors, order one and get someone who's experienced to replace it. My (ignorant) logic says that if the until functions after the said cap is replaced that would indicate that it was a single component failure. If the A700 still fails to produce audio then maybe another component had been smoking on the quiet too! and further investigation is needed.

Is this common sense AK members?

I've yet to find the gold Frakos whatever they may be. I will have another look tonight for them.