Waking up a Revox A700 - UK Vintage Radio Repair and Restoration Discussion Forum

Ted Kendall · 9th Oct 2016, 8:40 pm

This is a tale of "do as I say, not as I do".

I have several Revox A700s which were my main machines until various Studers arrived, when they went into store. To sort through the large number of tapes which have accumulated here, I decided to bring one back into domestic service. Readers of this forum will know that I bang on about replacing the Rifa 0.47uF capacitors in old Revoxes on sight, so of course I thought I could get away with a quick test "to see if anything else was wrong".

I did get away with it - for all of three minutes before the customary fffffffffT! noise, acrid smell and white smoke betokened the demise of one or more Rifas. There are nine in this particular A700, and all but two had obvious cracking of the case. Nine capacitors and a fuse later, I was back in business. I got lucky. You may not.

So, to reiterate, if you acquire a Revox A77, B77, A700 or PR99, seek out and replace ALL the Rifa 0.47uF capacitors before you do anything else. They look like polluted Fox's Glacier Mints, and it's not a question of whether they will fail, but when, and the consequences can be messy and unpleasant. You have been warned.

jamesperrett · 10th Oct 2016, 12:56 pm

I have a B77 which has been in fairly regular use since new and will probably continue to be regularly used for the foreseeable future. I was wondering whether the Rifa capacitors are more likely to fail after a period of storage or whether they fail during normal use?

Ted Kendall · 10th Oct 2016, 2:36 pm

Interesting point - I think disuse doesn't help matters - moisture ingress seems to be part of the failure mechanism, and regular use would ameliorate this - but if the encapsulation were not failing, the moisture wouldn't get in anyway.

I think the advice stands. If you acquire a machine, by definition you don't know its past history in detail and it is therefore sensible to assume that these components will be on the point of failure. Wholesale replacement is neither difficult nor expensive, certainly by comparison with the possible consequences of a failure.

When these machines were in daily use, I don't remember one Rifa going up, but they were decades younger then, and the caps have probably all had their design life and more by now.

This is a point worth wider consideration. With things like video recorders, DAT machines, and tape recorders, your choice is generally between an example which has been stored for years and consequently needs waking up, and one which has been in regular use for thirty years and hence is knackered anyway...

TIMTAPE · 11th Oct 2016, 2:33 am

Quote:

Originally Posted by jamesperrett

I have a B77 which has been in fairly regular use since new and will probably continue to be regularly used for the foreseeable future...

With the B77 there may be others but I can only recall one Rifa soldered across the mains supply after the power switch.

Ted Kendall · 11th Oct 2016, 10:32 am

There's certainly one on the capstan board as well - off-hand I'm not sure about the rest of it. Trouble with the cap across the mains is that it's quite well hidden by plastic on three sides, giving rise to exclamations of "What the

is going on?" when it goes up. At least, it did here.

TIMTAPE · 11th Oct 2016, 11:50 am

Agreed, I'd forgotten about the RIFA on the capstan motor board. I was more thinking the B77 doesnt have the RIFAs as on the A77's relay PCB.

jamesperrett · 11th Oct 2016, 1:51 pm

I'll bear this thread in mind when I get around to reviving the A77 that I also have here. it hasn't been used for many years but at least it has been stored in dry conditions.

Michael Maurice · 14th Oct 2016, 1:07 am

Quote:

Originally Posted by Ted Kendall

There's certainly one on the capstan board as well - off-hand I'm not sure about the rest of it. Trouble with the cap across the mains is that it's quite well hidden by plastic on three sides, giving rise to exclamations of "What the

is going on?" when it goes up. At least, it did here.

Also this capacitor is on the mains side of the switch, so switching the machine off, doesn't stop the capacitor from burning.

Ted Kendall · 14th Oct 2016, 7:51 am

Quite so - and half the beauty of it is that the firework display continues for about fifteen seconds - plenty of time for alarm and despondency to develop!

TIMTAPE · 14th Oct 2016, 10:34 am

Yes but once you've experienced it and found out the cause, it's not nearly so bad. I've had customers bring me such machines fearing the machine is probably beyond repair. Great relief for them when it's explained it's just one part worth small change that's failed and (usually) no other damage done.

9th Oct 2016, 8:40 pm	#1
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Waking up a Revox A700 This is a tale of "do as I say, not as I do". I have several Revox A700s which were my main machines until various Studers arrived, when they went into store. To sort through the large number of tapes which have accumulated here, I decided to bring one back into domestic service. Readers of this forum will know that I bang on about replacing the Rifa 0.47uF capacitors in old Revoxes on sight, so of course I thought I could get away with a quick test "to see if anything else was wrong". I did get away with it - for all of three minutes before the customary fffffffffT! noise, acrid smell and white smoke betokened the demise of one or more Rifas. There are nine in this particular A700, and all but two had obvious cracking of the case. Nine capacitors and a fuse later, I was back in business. I got lucky. You may not. So, to reiterate, if you acquire a Revox A77, B77, A700 or PR99, seek out and replace ALL the Rifa 0.47uF capacitors before you do anything else. They look like polluted Fox's Glacier Mints, and it's not a question of whether they will fail, but when, and the consequences can be messy and unpleasant. You have been warned.

10th Oct 2016, 12:56 pm	#2
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,873	Re: Waking up a Revox A700 I have a B77 which has been in fairly regular use since new and will probably continue to be regularly used for the foreseeable future. I was wondering whether the Rifa capacitors are more likely to fail after a period of storage or whether they fail during normal use?

10th Oct 2016, 2:36 pm	#3
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Waking up a Revox A700 Interesting point - I think disuse doesn't help matters - moisture ingress seems to be part of the failure mechanism, and regular use would ameliorate this - but if the encapsulation were not failing, the moisture wouldn't get in anyway. I think the advice stands. If you acquire a machine, by definition you don't know its past history in detail and it is therefore sensible to assume that these components will be on the point of failure. Wholesale replacement is neither difficult nor expensive, certainly by comparison with the possible consequences of a failure. When these machines were in daily use, I don't remember one Rifa going up, but they were decades younger then, and the caps have probably all had their design life and more by now. This is a point worth wider consideration. With things like video recorders, DAT machines, and tape recorders, your choice is generally between an example which has been stored for years and consequently needs waking up, and one which has been in regular use for thirty years and hence is knackered anyway...

11th Oct 2016, 10:32 am	#5
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Waking up a Revox A700 There's certainly one on the capstan board as well - off-hand I'm not sure about the rest of it. Trouble with the cap across the mains is that it's quite well hidden by plastic on three sides, giving rise to exclamations of "What the is going on?" when it goes up. At least, it did here.

11th Oct 2016, 11:50 am	#6
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Waking up a Revox A700 Agreed, I'd forgotten about the RIFA on the capstan motor board. I was more thinking the B77 doesnt have the RIFAs as on the A77's relay PCB.

11th Oct 2016, 1:51 pm	#7
jamesperrett Octode Join Date: May 2007 Location: Liss, Hampshire, UK. Posts: 1,873	Re: Waking up a Revox A700 I'll bear this thread in mind when I get around to reviving the A77 that I also have here. it hasn't been used for many years but at least it has been stored in dry conditions.

14th Oct 2016, 7:51 am	#9
Ted Kendall Dekatron Join Date: Jul 2008 Location: Kington, Herefordshire, UK. Posts: 3,670	Re: Waking up a Revox A700 Quite so - and half the beauty of it is that the firework display continues for about fifteen seconds - plenty of time for alarm and despondency to develop!

14th Oct 2016, 10:34 am	#10
TIMTAPE Octode Join Date: Jul 2006 Location: Perth, Western Australia Posts: 1,969	Re: Waking up a Revox A700 Yes but once you've experienced it and found out the cause, it's not nearly so bad. I've had customers bring me such machines fearing the machine is probably beyond repair. Great relief for them when it's explained it's just one part worth small change that's failed and (usually) no other damage done.