Powering up old stuff that's not been run for several years

[Cursitor Doom]

I don't think any of us here would take some semi-ancient item of
electronic equipment of unknown provenance and just plug it in the mains
socket and switch on. We know from experience or elsewhere that is not an
advisable thing to do. So we typically gently wind up the voltage via a
variac over an extended period of time. But is that enough? I read
somewhere one should also monitor the current drawn by the equipment as
one does this. I admit I've never been quite that fussy, but would be
interested in hearing what others think about this rather more cautious
approach and if it actually achieves anything worthwhile.

 

[pfjw@aol.com]

Rant pending as I am traveling. But it is better to dump equipment in salt water than to apply power without a precise means of monitoring it. Dim bulb devices notwithstanding.


Peter Wieck
Melrose Park, PA

 

[Phil Hobbs]

On 11/03/2016 12:19 PM, Cursitor Doom wrote:

I don't think any of us here would take some semi-ancient item of
electronic equipment of unknown provenance and just plug it in the mains
socket and switch on. We know from experience or elsewhere that is not an
advisable thing to do. So we typically gently wind up the voltage via a
variac over an extended period of time. But is that enough? I read
somewhere one should also monitor the current drawn by the equipment as
one does this. I admit I've never been quite that fussy, but would be
interested in hearing what others think about this rather more cautious
approach and if it actually achieves anything worthwhile.

Well, maybe if it has an old school 50/60 Hz transformer, rectifier, cap
power supply. I don't have a lot of those sorts of things.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

 

[N_Cook]

On 03/11/2016 16:19, Cursitor Doom wrote:

I don't think any of us here would take some semi-ancient item of
electronic equipment of unknown provenance and just plug it in the mains
socket and switch on. We know from experience or elsewhere that is not an
advisable thing to do. So we typically gently wind up the voltage via a
variac over an extended period of time. But is that enough? I read
somewhere one should also monitor the current drawn by the equipment as
one does this. I admit I've never been quite that fussy, but would be
interested in hearing what others think about this rather more cautious
approach and if it actually achieves anything worthwhile.

Variac yes, meter or lamp for current behaviour yes . One cheap-now
extra, monitor with a small simple IR thermometer for any hot spots, not
the large ones for car engines but key-fob size that you can really get
inside kit with . Note, at the collector has to be metal, shrink some
heatshrink over the outside of the collector cone to avoid any short
circuits

 

[Jon Elson]

Cursitor Doom wrote:

I don't think any of us here would take some semi-ancient item of
electronic equipment of unknown provenance and just plug it in the mains
socket and switch on. We know from experience or elsewhere that is not an
advisable thing to do. So we typically gently wind up the voltage via a
variac over an extended period of time. But is that enough? I read
somewhere one should also monitor the current drawn by the equipment as
one does this. I admit I've never been quite that fussy, but would be
interested in hearing what others think about this rather more cautious
approach and if it actually achieves anything worthwhile.

If not tantalum capacitors, and simple linear power supply, then this is
usually a good idea.

Tantalum caps can also be helped by this, but appluing very small voltages
for a long time (a day or so) may be better before more power is applied.
Replacing them is another way to go.

Slowly ramping up voltage is not generally compatible with switching
supplies.

Jon

 

[Phil Allison]

Cursitor Doom wrote:

I don't think any of us here would take some semi-ancient item of
electronic equipment of unknown provenance and just plug it in the mains
socket and switch on. We know from experience or elsewhere that is not an
advisable thing to do. So we typically gently wind up the voltage via a
variac over an extended period of time. But is that enough? I read
somewhere one should also monitor the current drawn by the equipment as
one does this. I admit I've never been quite that fussy, but would be
interested in hearing what others think about this rather more cautious
approach and if it actually achieves anything worthwhile.

** I've been using a variac plus RMS current meter for 30 years and also see a lot of gear that has been out of use for over a decade, mostly tube amplifiers.

Providing you have a good idea what the AC draw should be under idle and standby conditions, you can apply full supply voltage in a short time if the draw seen rises smoothly towards the expected value.

Of course you need a decent current meter to do this, a 10amp moving iron type is not adequate. I use a dedicated 3.5 digit LED meter with internal RMS converter.



..... Phil

 

[pfjw@aol.com]

And.... Here is the rant, from 2006. It was written for the vintage radio group - so "radio" is used instead of "about anything mains-powered with capacitors".


RANT WARNING RANT WARNING RANT WARNING
Well, I might spare you, IF: you have voltage _and_ current meters for
this variac that are capable of accurately representing 0.01A and 2-3V
AC. If you have this capacity and use it *every* time you use a variac,
then ignore the following.

Otherwise, a variac is worse-than-useless for radio work, fit only for
dimming lights without excessive rF noise. I cannot think of a single
use for them (without meters) that a dim-bulb tester will not do with
equal accuracy, far greater safety and less cost (of course). The
typical urban-myth uses for a variac:

a) Apply power to a radio slowly to see how it starts without letting
out the 'magic smoke': Yeah, right. How would you know unless you
either see sparks (it's too late then), or have a current meter on the
thing to see that it is pulling 65 watts when it really only should be
30. A radio might even work just-fine-and-hum-free as far as ears are
concerned, but if it is pulling those extra 5-10 watts, that is all
being expressed as heat somewhere, usually in an unobtaium part. Can
you say *POOF*?

b) Reforming caps: Unless a radio has a SS rectifier, this is simply
silly. A tube rectifier won't pass current until about 75% or-so of
rated filament voltage. So, hitting the caps with 75% of B+ hardly is a
slow reform.

c) Running radios at the "proper" voltage: Great, until they leave the
bench.

d) Dimming lights... Yep, that's what unmetered variacs are best at.
Other thanbas ballast and as doorstops.

END RANT

In all seriousness, unmetered variacs are silly, stupid, dangerous
items for electronics use, and for any of several reasons. Spend the
money where it will do some good, such as an isolation transformer. If
you have one of those, then look for a metered variac, or the meters to
add to the one you have.

 

What you said, or reranted is not wrong in some instances. One notable exception is audio amps that use VFETS for outputs, which are depletion mode and WILL fry if you try to run the up slow on a variac, at least in the Sony ones. I don't know of any others but to be tolerant of low AC input it would take a quite special design with abnormal conditions in mind. I worked for a Sony Signature dealer and ASC back before their product turned to real shit and I can tell you that i n most cases, abnormal conditions were not on their engineers' minds.

Dim bulbs and variacs come in handy when you have repaired most regular solid state amplifiers. Once you drop $35 worth of silicon in them for a fried channel it is nice not to have all that short out in the first millisecond..

With most tube stuff, honestly I would just plug it in. Possible exceptions would be if it has selenium rectifiers. Even moreso a high end tube amp with a big old 5U4 but using a selenium rectifier for the negative bias to the outputs.

Bottom line is you can't just make a blanket statement about working on all equipment. And with the advent of the SMPS, there are even less assumptions that can be made. You can usually use a DBT on like a DVD player or something like that and it will keep the smoke in in most cases. But the normal current drain is usually so low all a hundred watt bulb will do is keep you from burning foil off the PS board. Some short on the five volt line is not protected and if it is going to fry something it is going to succeed. Then, if you use a lower wattage bulb, some SMPSes won't start.

Before I got kicked off AK they were always talking about the DBT. And really it does prevent pretty much all board burning. You burn the foil of a circuit board it is not fun to fix, especially with audiophiles who are going to want your repair to follow the same path as the original foil. I have done that type of rework but really most of the shit today does just fine with jumper wires.

Lately I am dealing with a design defect in amps built by Apex for RSQ, KDS and Technical Pro. All a bunch of liars on the power specs, Technical Pro claims like 1,300 watts or something on an amp that actually puts out about 90 watts a channel. The defect is that the assholes thought the bias regulator would just hold itself to the heatsink. Well they don't, and now ater going through several options we just could not make happen I am simply gluing them. Got me some JB Weld and made some clamps out of a couple of coat hangars. How is that for factory service ?

Enough rant, back to the subject. The DBT and variac have actually lost some of their usefulness. They are not useless but it does depend on what you are working on. Old tube stuff I would just plug in. For a few seconds. then I would remove all the tubes ad plug it in for longer. then I would put in the rectifier tube and see what happens to the current draw, with all the other tubes out. Scope the caps, if all the other tubes are not in there and you got ripple you got a problem. Turn if off before you blow that 5U4, which is no longer available for $3. The shipping is more than $3.

I have had a pretty diverse career and even got a little bit into CNC machines but not much. I learned automotive electronics when they started with those ECMs and shit. We flipped cars, and the reason we made money was because the backyard mechanics could not understand electronic and My Goodwrench forgot there was an actual engine under all that shit. I beat them several times in troubleshooting. Three of them making fifty bucks an hour looking at a computer readout and can't tell you have a burnt valve or a fouled plug. And the idiots probably made more money than me.

If you think powering up old electronics is scary, try starting an old car that has been sitting for 20 years or more. That's why some people actually take them apart first.

Well not completely apart but they will do a compression check, change the oil, whatever they can coax out of the crankcase that is and put new oil in it, drain the gas tank, pressure check the cooling system maybe, but that can come later after the thing actually starts.

Everything requires a slightly different approach.

 

[pfjw@aol.com]

I took my 48 hour rule before replying - hip-shots often ricochet.


On Friday, November 4, 2016 at 7:13:46 PM UTC-4, jurb...@gmail.com wrote:

> What you said, or reranted is not wrong in some instances. One notable exception is audio amps that use VFETS for outputs, which are depletion mode and WILL fry if you try to run the up slow on a variac, at least in the Sony ones. I don't know of any others but to be tolerant of low AC input it would take a quite special design with abnormal conditions in mind. I worked for a Sony Signature dealer and ASC back before their product turned to real shit and I can tell you that i n most cases, abnormal conditions were not on their engineers' minds.

Consider that statement - it suggests that a brown-out would fry the equipment. Brownouts are quite common in certain regions of the US (sadly) and though rare in our particular case, we are on a double-fed distribution line as there are neighbors with mains-powered life-support equipment nearby. What will happen under extreme storm conditions (twice in 8 years) is that one end of the line may short due to a tree fall or similar, and draw available current (and voltage) way down. Hell on motor-based equipment such as refrigerators or freezers and some electronics. But, we have suffered no failures as a result. Yes, the critical 'stuff' is on surge protectors, but the point is that consumer equipment should be somewhat resilient and designed for real-world occurrences. I have to ask, have you personally observed such a failure due to such a cause?

Dim bulbs and variacs come in handy when you have repaired most regular solid state amplifiers. Once you drop $35 worth of silicon in them for a fried channel it is nice not to have all that short out in the first millisecond.

With most tube stuff, honestly I would just plug it in. Possible exceptions would be if it has selenium rectifiers. Even moreso a high end tube amp with a big old 5U4 but using a selenium rectifier for the negative bias to the outputs.

And a dead-shorted filter cap would do *WHAT* in ten seconds? Or a shorted rectifier tube? How much current for how long to wipe out an output transformer? Remind me not to send you any of my vintage equipment for repairs...

> Bottom line is you can't just make a blanket statement about working on all equipment. And with the advent of the SMPS, there are even less assumptions that can be made. You can usually use a DBT on like a DVD player or something like that and it will keep the smoke in in most cases. But the normal current drain is usually so low all a hundred watt bulb will do is keep you from burning foil off the PS board. Some short on the five volt line is not protected and if it is going to fry something it is going to succeed. Then, if you use a lower wattage bulb, some SMPSes won't start.

I am not so sure that the OP was concerned about equipment made after the year 2000, and/or equipment that has been sitting on a shelf for six months. I believe the thrust was towards equipment that has been sitting in a barn, cellar, shelf or garage for 20 - 60 years. Nor would I spend that much time on a consumer commodity, the repairing of which would likely cost more than a new one - were it even possible.

> Before I got kicked off AK they were always talking about the DBT. And really it does prevent pretty much all board burning. You burn the foil of a circuit board it is not fun to fix, especially with audiophiles who are going to want your repair to follow the same path as the original foil. I have done that type of rework but really most of the shit today does just fine with jumper wires.

Getting kicked off AK is not difficult. Probably speaks well of you that you were. As to Dim Bulb Testers - they have their (very limited) uses as something of a protective device. They will reduce immediate damage (those first 15 seconds) but they are NOT suitable as a final indicator.

> Lately I am dealing with a design defect in amps built by Apex for RSQ, KDS and Technical Pro. All a bunch of liars on the power specs, Technical Pro claims like 1,300 watts or something on an amp that actually puts out about 90 watts a channel. The defect is that the assholes thought the bias regulator would just hold itself to the heatsink. Well they don't, and now ater going through several options we just could not make happen I am simply gluing them. Got me some JB Weld and made some clamps out of a couple of coat hangars. How is that for factory service ?

You well know that equipment is built down to the price/purchase point. Where it is perfectly possible, even today, to purchase 'good stuff' at a decent price, the research required to do so is considerable. This applies to anything from appliances to shoes or toys.

> Enough rant, back to the subject. The DBT and variac have actually lost some of their usefulness. They are not useless but it does depend on what you are working on. Old tube stuff I would just plug in. For a few seconds. then I would remove all the tubes ad plug it in for longer. then I would put in the rectifier tube and see what happens to the current draw, with all the other tubes out. Scope the caps, if all the other tubes are not in there and you got ripple you got a problem. Turn if off before you blow that 5U4, which is no longer available for $3. The shipping is more than $3.

*NOTHING*, repeat, nothing 'just gets plugged in' on my bench. Even if I am not doing the 'variac' thing for modern solid-state stuff, I will pre-set the voltage at 118V and then turn on the item to watch how much current it draws. Anything with a tube gets the full treatment.

I have had a pretty diverse career and even got a little bit into CNC machines but not much. I learned automotive electronics when they started with those ECMs and shit. We flipped cars, and the reason we made money was because the backyard mechanics could not understand electronic and My Goodwrench forgot there was an actual engine under all that shit. I beat them several times in troubleshooting. Three of them making fifty bucks an hour looking at a computer readout and can't tell you have a burnt valve or a fouled plug. And the idiots probably made more money than me.

If you think powering up old electronics is scary, try starting an old car that has been sitting for 20 years or more. That's why some people actually take them apart first.

A 1968 VW beetle in 1992, the car had not run since 1970.
a) Drain oil.
b) Mix one quart 30W oil with one gallon kerosene.
c) Pour into crankcase.
d) Remove spark plugs.
e) Squirt an ounce of Marvel Mystery Oil into each cylinder.
f) Turn driveshaft by hand ten full turns.
g) Drain kero mixture.
h) Allow to sit overnight.
i) Re-squirt MMO.
j) Turn ten times again.
k) Add correct amount of 30W oil.
l) Install new spark-plugs.
m) Points-condenser-rotor-cap-wires

Start. Run at idle for 15 full minutes. Gradually run up to 2,000 rpm, hold at 2,000 rpm for 10 minutes. Check for any oil leaks - and there will be some! Run for one hour, varying rpm from idle to 3,500.

It also works on water-cooled engines - I did roughly the same thing to a Mercedes 220 back in the day with good results.

> Well not completely apart but they will do a compression check, change the oil, whatever they can coax out of the crankcase that is and put new oil in it, drain the gas tank, pressure check the cooling system maybe, but that can come later after the thing actually starts.

I cannot imagine doing a compression check on an engine that has sat idle for even a year without bad results - scored cylinders at the least. That is the point of the MMO and hand-turning.

Everything requires a slightly different approach.

Surely. But first principles do apply.

Peter Wieck
Melrose Park, PA