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Old 22nd Apr 2021, 1:58 pm   #1
AmplifyAudio
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Default Waking up and testing Trinitron monitors

Hey everyone!

Just after a bit of advice on testing some old 21" CRT monitors that haven't been used for around 10 years or so, although one hasn't been powered in nearly 25 years!

I've got a decent variac and one of those plug in power monitors, but I've not used this set-up on any 'modern' and/or complex electronic devices before, just simple tube amps and the occasional radio.

To be honest, I'm probably being a bit over cautious as they have all been stored in my office, which is dry and fairly clean, not a rotting shed! But I'd rather not have any of them going bang!

Any advice or anything to watch out for? Other than excessive current draw and magic smoke, that is!
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Old 22nd Apr 2021, 2:13 pm   #2
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Default Re: Waking up and testing Trinitron monitors

Hi AA, you might find more specific advice for this in the 'Vintage Television And Video' section as that's where all the CRT experts mainly hang out.
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Old 23rd Apr 2021, 1:04 am   #3
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Default Re: Waking up and testing Trinitron monitors

Dammit, I knew that!

I agonised for minutes over where to post this! Thanks, I'll ask for it to be shifted!
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Old 23rd Apr 2021, 5:54 am   #4
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Default Re: Waking up and testing Trinitron monitors

It is a bad idea to use a variac on anything with a switched-mode power supply. It will fight against the reduced voltage by trying to draw more current.
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Old 23rd Apr 2021, 9:55 am   #5
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Default Re: Waking up and testing Trinitron monitors

I recently did this with some CRT sets that had been in storage since about 2009. Some not in ideal conditions either. I just applied full mains for a few minutes at a time, listening and watching all the time for distress. Worked out well.
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Old 23rd Apr 2021, 9:57 am   #6
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Default Re: Waking up and testing Trinitron monitors

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Originally Posted by julie_m View Post
It is a bad idea to use a variac on anything with a switched-mode power supply. It will fight against the reduced voltage by trying to draw more current.
<Massive facepalm> Yes. Yes, of course it will. They all have SMPSs. You'd think I would of twigged while checking them over and seeing the voltage specs of 100-240VAC 50/60Hz on each one!

Thanks!
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Old 23rd Apr 2021, 10:47 am   #7
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Default Re: Waking up and testing Trinitron monitors

A Variac will indeed blow or a good chance with these power supplies , due I believe to upsetting the "mark space" ratio.

Just check around first for any suspect caps and then as suggested short runs of full mains.
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Old 23rd Apr 2021, 12:06 pm   #8
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Default Re: Waking up and testing Trinitron monitors

Just plug them in, I have had solid state equipment stored for over 20 years and have had no real problems.
But check that the plug has a 5 amp fuse fitted.


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Old 23rd Apr 2021, 12:16 pm   #9
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Default Re: Waking up and testing Trinitron monitors

Don't plug them in just yet!

First replace any and all RIFA paper capacitors in the power supplies, if present.
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Old 23rd Apr 2021, 3:23 pm   #10
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Default Re: Waking up and testing Trinitron monitors

very Very VERY VERY bad idea to put a Sony 21' monitor on a variac.

I found out that they have a thick film microcircuit which switches their main rectifier (on the mains input) between bridge and voltage doubler modes to handle mains in the 120v countries and 240v.

The circuit spots mains coming up, decides on where in the world it must be, and then locks in that rectifier mode. It does not change its mind even if the voltage keeps on going higher. Eventually big breakdown diodes do their job and pull the fuse. However, the diodes also die in doing so. If someone just replaces the fuse and tries again, the main electrolytics will let go as well as the SMPS transistors etc.

Some neds threw a lump of chain or wire rope they found in a field across an 11kV feeder a couple of miles away from HP's plant. The mains went down in the area and the network made re-start attempts before the affected branch was isolated. We saw all the lights go off, then half-voltage start attempts, then all came back up. We lost monitors totalling 3/4 of a million quid. As they were HP branded ones, the warranty was from HP not Sony. HP did not warrant stuff sold from one division to another.

The accountants set about planning the purchase of replacements, managers started planning priorities to have minimum impact on income and product intros.

This mere engineer took one apart and found two protection diodes and a fuse would get mine going. I ordered up a job lot of fuses, diodes, and I decided to do bridges and reservoirs just to play safe. Two happily glowing monitors on my desk got noticed... I fixed a number for various people. HP had a wee word with Sony, and Sony sent a bunch of people to repair all the monitors in the place. They remained vulnerable to an action replay of the event, but we now knew the recipe.

As design whoopsies go, chalk this one up as a biggie.

So, now you know the pitfall, don't risk falling in!

David
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Old 23rd Apr 2021, 3:30 pm   #11
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Default Re: Waking up and testing Trinitron monitors

SGI also badged Sony monitors and I have known the same thing happen - the older models without the auto select PSU gave no problems...
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Old 23rd Apr 2021, 6:47 pm   #12
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Default Re: Waking up and testing Trinitron monitors

Agreed: don't power a switched-mode-PSU monitor with a variac.

Even if it doesn't 'latch' into "I'm-being-fed-fron-120V-so-need-to-arrange-my-input-to-voltage-doubling-mode" which results in a horrorshow when you turn the supply up to 240V, if the supply has any sort of peak-current-draw constraint the poor SMPS will strive to achieve its designed output-voltages by demanding more and more current from the supply (to compensate for the low supply-voltage) - and the poor switcher's power-transistors can go into meltdown.

"Lamp Limiters" and variacs can easily kill an otherwise-entirely-healthy 1970s/80s/90s/2000s power-supply.
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Old 23rd Apr 2021, 10:08 pm   #13
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Default Re: Waking up and testing Trinitron monitors

Lamp limiters and variacs are for valve equipment and linear power supplies only.
NEVER for SMPS. Some sets service manuals would even tell you not to use a variac in the notes.

Another that blew up with them was the Tandberg CTV2 my foreman couldn't fix one after many attempts and it was returned to Tandberg, on return a label was attached with a warning about using a varaic. After he fixed many of them like the rest of us did with no further issues.
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Old 23rd Apr 2021, 10:39 pm   #14
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Default Re: Waking up and testing Trinitron monitors

Quote:
Originally Posted by mark pirate View Post
Just plug them in, I have had solid state equipment stored for over 20 years and have had no real problems.
But check that the plug has a 5 amp fuse fitted.
I have an old but reliable RS RCD plug top device to trailing socket fitted with an ancient 2A fuse that I use for every DUT!

Quote:
Originally Posted by Maarten View Post
Don't plug them in just yet!

First replace any and all RIFA paper capacitors in the power supplies, if present.
Definitely won't be doing that! I'm selling them as working but as is, I just don't have the time to start changing things in them! In fact, just lugging them around and getting a couple of shots of a good raster is a bit of an imposition!

Quote:
Originally Posted by G6Tanuki View Post
Agreed: don't power a switched-mode-PSU monitor with a variac.
"Lamp Limiters" and variacs can easily kill an otherwise-entirely-healthy 1970s/80s/90s/2000s power-supply.
Nope! Won't be! In my defence (yer 'onner) however, I used to mainly repair valve gear and have been out of the repair game for 10 to 15 years, so I've forgotten most of it! In addition some of the very newest modern switchmode amps we use in the live industry are simply astonishing. The L'Acoustics LA8s that keep the entire PA going for 4 or 5 seconds when the single genny running the stage farts and splutters into a stall are very impressive! The you get Powersoft amps. They demoed their new models a couple of years ago. Included in the demo was playing a sine through one amp, then powering a second amp from the speaker o/p. Yeah, powering it. Utterly impressive silliness!

Anyway, thanks for all the great and helpful replies! Of course there is a SMPS in a modern CRT! Seeing as I've not been doing actual electronics for a fair few years, I have forgotten a lot. Brain like a... er... erm... the thing, net thing with a handle, metal net though... Er...
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Old 24th Apr 2021, 1:57 am   #15
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Default Re: Waking up and testing Trinitron monitors

If you remove those voltage switches most models just remain in 240 volt mode and will work fine on sloppy mains supplies and often will go on to tolerate starting up on a Variac.
Quite a bit of modern kit has a wide enough pulse width range and low enough on resistance FET to cover 100 to 250 volts without any switching at all.
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Old 24th Apr 2021, 8:03 am   #16
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Default Re: Waking up and testing Trinitron monitors

Quote:
Originally Posted by AmplifyAudio View Post

Quote:
Originally Posted by Maarten View Post
Don't plug them in just yet!

First replace any and all RIFA paper capacitors in the power supplies, if present.
Definitely won't be doing that! I'm selling them as working but as is, I just don't have the time to start changing things in them! In fact, just lugging them around and getting a couple of shots of a good raster is a bit of an imposition!
Checking whether there are any (if UK or German made there might be) and just cutting them out is also an option. Problem with selling equipment using RIFA's is that the buyer will complain about the smoke when he plugs in the set.
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Old 17th May 2021, 12:59 am   #17
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Default Re: Waking up and testing Trinitron monitors

Bit of an update:

Using a power meter plug device thingy with my ancient RS RCD plugtop and low current fuses, they all powered up and got straight on with the job of being a CRT monitor, rather than boxes of impromptu fireworks. A couple of hours test of each one and a quick go on the PAT machine, all good!

Very happy to not have any magic smoke escaping at all, especially as I don't even know where you can get replacement magic smoke from these days!
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Old 17th May 2021, 7:18 pm   #18
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Default Re: Waking up and testing Trinitron monitors

Out of interest, how had they been stored ? In the warm and dry or a cold, damp shed/outbuilding ?
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Old 18th May 2021, 2:44 am   #19
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Out of interest, how had they been stored ? In the warm and dry or a cold, damp shed/outbuilding ?
All in the house/office, no damp, some heating and minimal cobwebs.

On reflection I've been a fair bit bit over cautious. In the back of my mind, I knew they would be probably OK. But I've been detached from electronics repairs for over 10 years. In my defence though I seriously dislike any loud surprises, flashes, releases of magic smoke, even static!

Even today where I was replacing a few capacitors in the control module of my wife's campervan gas water heater, my smartwatch notified me of notifications. Completely drained PCB and still I jumped out of my skin because I forgot to take the watch off!
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