Tek 545B O'scope Fuse and Power

So, I recently got a Tektronics 545B oscilloscope. It's been sitting in a b asement for god knows how long, and I thought it would be cool to see if it worked. well, it doesn't. It's missing it's fuse and fusecap, and it's pow er cable. I had read in a couple of places that the fuse only affected the high voltage stuff, like the CRT. I might be totally wrong about this, whic h is why I'm asking you guys :) Well, with that in mind, I found a newer po wer cable that seemed to fit the bill, so I tried using that. Nothing. I th en tried using a voltage regulator. Still nothing. Now, I'm not sure if it' s because of the mysterious missing fuse, or if something else has gone bad inside, or if it was the power cable (which I doubt). My next guess was th at it was the missing fuse. Holy crap does this thing have a strange fuse. I've looked all over for something with a similar rating and size, but with no luck. I'm not as worried about the fusecap. I searched for a couple wee ks online, but I eventually came to the conclusion that the thing would pro bably never work. Today though, I thought I'd give it a go again. Back of the oscilloscope:

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I opened it up to find TONS of gunk and dusk blanketing it's insides. I als o found a pdf of its manual (which has slightly more info about the missing fuse). Now I think I got in over my head, because I'm too scared to touch anything. Before I go fiddling with 50 year old electrical components, I wa nt to know if it works or not, what I can do to fix the fuse situation (eve n if only temporarily), and if I should check for anything else.

So, can anyone help me? I'd REALLY like to get this guy working again, but I need some help (obviously, hehe...)

Reply to
Noel Keith
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So, can anyone help me? I'd REALLY like to get this guy working again, but I need some help (obviously, hehe...)

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There is a Yahoo group dedicated to the old Tektronix scopes. Why don't you join it and ask there?

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Over 6000 members, sure to be someone that can lend you some guidance.

The usual way to clean these scopes out is with soap and hot water. That subject is covered on the group.

regards, tm

Reply to
tm

The last time I saw one of those was in the '80s and they were very old then. The fuse is needed for any operation, and what good would a 'scope be without the CRT powered, anyway?

For pursuing an interest in electronics, you would likely be far better off with a 'scope of more recent vintage. You may find cheap/free equipment in local Craigslist or Freecycle listings.

You may be in over your head suggested by the details you've posted. If you chance applying power, be ready to interrupt the power quickly (switched receptacle) and have another capable person present.

If this 'scope has been sitting around in a damp location, it may be too dangerous to go thru the effort of applying power. A proper ground wire should be attached to the case and a known good earth ground before applying power. Depending on a used or old deteriorated power cord could be a mistake. If the 'scope is powered, it should not be left unattended and should absolutely be disconnected from the AC power afterward.

Ask around to see if there may be any ham radio enthusiasts near you, who might power up the 'scope for you. An elder person may be more familiar with old, neglected tube equipment and more likely to have the correct type of fuse holder cap.

The fuse holder cap is a bit obscure nowadays.. it has a tubular projection with 2 wings? at the end. With a fuse inserted into the cap, the fuse is then slid into the holder until it is fully inserted, then the cap is turned clockwise about 90 degrees (maybe less but not more). The fuse cap will then be latched into place.

Obviously, a lot of debris isn't good in an electrical appliance, but any cleaning should be done cautiously and gently with no power applied and better to do it outdoors (low pressure compressed air or duster can gas, for example).

I'm not sure about that particular model, but check your literature to see if there is an opening in a side panel where jumper bars go (banana plug sockets 2 rows of 3 IIRC). There won't be any trace response without those jumpers in the correct positions. If applicable to this model, the said banana sockets are accessible with the covers ON, nothing inside needs to be jumpered for normal operation.

--
Cheers, 
WB 
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Reply to
Wild_Bill

Of course the fuse takes care of the whole thing, it's in the primary to the power transformer. F601, it's a 6amp fast-blo 3AG fuse for 120vac operation (3ampts if running off 240v). It's a standard glass fuse, you should be able to get them anywhere. It goes into the fusecap, then you screw (or is it turn?) the fusecap into the holder at the back of the scope. I don't know where the fusecaps can be found these days, I suddenly find I need one and can't find any among all the junk.

Nothing will happen unless that fuse is in place, and that includes the fusecap.

There's also a thermal cutout fuese in series to the primary of the power transformer, but that isnt' even a factor until you get the proper fuse in there witha fusecap.

I got one 20 years ago, though havent' had it on in about 10 years. It was working fine when I got it, but I since someobody found it at a hospital as it was about to be tossed out, I suspect it was still in operation. It worked for a while, then the trace got bent. It's a multiple section power supply I wasn't sure which section was the problem, I found it by taking the probe and touching each of the sections across their filter capacitor, until the waveform got worse. Changed that filter capacitor, and all was fine. It is incredibly bulky, which is why I moved it to the basement and thus it's a lot less useful, so it just sits there.

Michael

I searched for a couple weeks online, but I

need some help (obviously, hehe...)

>
Reply to
Michael Black

"Michael Black"

** As marked on the rear of the scope - the fuse needs to be a "slow blow" type.

It's a standard glass fuse, you should be able to get them anywhere.

** Well, anywhere that has available a good range of fuses for electronic equipment.

Slow blow fuses are commonly stamped or marked with a "T" before the amp rating.

So look for a " T6.3A " fuse in 3AG size ( or 32 x 6.3 mm) - though such as high value seems wrong for a tube scope.

If you use a standard "fast " fuse, it may well blow at switch on.

.... Phil

Reply to
Phil Allison

To make a correction, when I got the scope I DID have the fuse. It had fall en out somwhere when I took it home though. I had no luck finding it. The t hing is, I haven't been able to find a slow blow fuse with the right Amp/Vo lt ratio. Currently I just want to see if I can get the power light to turn on. As long as I know it's getting power, I can work from there. It's been in a pretty dry area (but dirty-ish), so I would be suprised if something was damaged in there. The guy I got it from said it worked when he got it, but that was several years ago...

I also sorta lied about me having to electronics experience, actually. I'm an electronic musician and I've been experimenting with making my own synth s. In fact the reason I'm fixing this up is to hook it up to my synths and see the waveforms, just as a way to show it off (and also to keep the house warm in the winter hehehe). Now that I'm looking at it, it seems to be in pretty good condition! Hmmm... I don't suppose there would be any way to su btitute anything else for the fuse? That is, without blowing it up.

Reply to
Noel Keith

"Noel Keith"

The thing is, I haven't been able to find a slow blow fuse with the right Amp/Volt ratio.

** LOL - there no such thing.

The 3AG fuse you need will be probably be marked:

" T6.3A 125V " OR " T6.3 250V "

Sometimes the T is left off and the slow blow characteristic is identifiable by having a coil spring or long spiral inside the glass.

.... Phil

Reply to
Phil Allison

I think that you really are over your head with this old scope if you can't deduce that a missing fuse is probably the reason that it doesn't light up. This scope isn't for the faint of heart to work on. Since it's been idle for who knows how long, then it's almost ceretain that most, if not all, of the power supply filter capacitors need to be replaced, along with many more electrolytics in other circuits. Most of the power supply sources in it are regulated, and sometines even an experienced technician can find them hard to get right. Ripple and noise on the voltage sources are critical to proper operation of every circuit in the scope. As for the dirt, I understand that the Tektronix service dept used to actually wash scopes that had been traded in for newer better scopes down with detergent and a low pressure garden hose. Then the scopes were air dried for several days (in a warm, dry place). Then, repair and calibration were performed.

The scope can almost certainly be restored to working condition, but that usually takes someone with proper knowledge, experience and test equipment. You need another scope and a good DMM just to get the power supplies running properly,

--
Dave M
Reply to
Dave M

"Dave M"

** I take it the scope has a fan inside - right ?

Many times I have had to give large power amps a " bath " for the same reason.

Plus, on one occasion, because the customer's storage shed for his hire business had been flooded with muddy storm water.

.... Phil

Reply to
Phil Allison

I couldn't be bothered going down to the basement to check, the manual was handy. The parts list says fast-blo. The odd thing about the manual is I see no photo of the back panel.

Which makes sense, and I just copied what was in the manual. I turn mine on, and the lights dim. If it was fast, you're right, that kind of inrush would blow the fuse before the thing had a chance to take off.

Michael

Reply to
Michael Black

** So the thick plottens .......

Seems there is disagreement between the manual and the labelling on the back.

A "T 6.3" amp fuse is too big for a tube scope - but an "F 6.3" amp fuse would be about right, given the inrush surge of the circa 200VA supply transformer.

.... Phil

Reply to
Phil Allison

basement for god knows how long, and I thought it would be cool to see if it worked. well, it doesn't. It's missing it's fuse and fusecap, and it's power cable. I had read in a couple of places that the fuse only affected the high voltage stuff, like the CRT. I might be totally wrong about this, which is why I'm asking you guys :) Well, with that in mind, I found a newer power cable that seemed to fit the bill, so I tried using that. Nothing. I then tried using a voltage regulator. Still nothing. Now, I'm not sure if it's because of the mysterious missing fuse, or if something else has gone bad inside, or if it was the power cable (which I doubt). My next guess was that it was the missing fuse. Holy crap does this thing have a strange fuse. I've looked all over for something with a similar rating and size, but with no luck. I'm not as worried about the fusecap. I searched for a couple weeks online, but I eve ntually came to the conclusion that the thing would probably never work. Today though, I thought I'd give it a go again.

found a pdf of its manual (which has slightly more info about the missing fuse). Now I think I got in over my head, because I'm too scared to touch anything. Before I go fiddling with 50 year old electrical components, I want to know if it works or not, what I can do to fix the fuse situation (even if only temporarily), and if I should check for anything else.

need some help (obviously, hehe...)

When I was a calibration tech for Collins Radio in Richardson, TX we had a wash cabinet for washing out dirty electronics equipment. It had a turntable in it and a spray head to rinse it off. We just sprayed things with soap solution and rinsed them off, then put them in an oven set at around 120 degrees over night. Paper covered electrolytics needed to be wrapped to keep the paper from getting wet.

The scope will probably need to have the filters replaced. If it has an old fashioned selenium rectifier that will undoubtedly need to be replaced. Early models had the seleniums, unless I am remembering the 545A. And there is a fair chance a bunch of tubes will be weak. This is particularly important for the power supply regulator tube(s). I don't remember if it had 1 or 2 series regulators. If you have the manual you can tell easy enough.

Bill

Reply to
Bill Gill

Alright, so I was able to find 2 types of fuses that I THINK should work. O nly thing is that they're ceramic, and not glass, but it shouldn't matter.

6.3A 250V Slow Blow, and 6.3A 125V Slow Blow. They were cheap so I bought 5 of each, just in case I needed a backup for whatever reason. I'm also look ing for a F6.3A fuse now too. I did manage to get some life in to it though . A buddy of mine who works on these things came over and brought a spare f use from another Tek scope of his and said he wanted to see if it worked. W ell, it blew instantly. But...hey! At least I got it to do something, right ?...right? Also, the fan turned on for that brief moment of life and was sl owly spinning.
Reply to
Noel Keith

"Bill Gill".

** Is there some kind of rule that makes Americans refer to all liquid detergents as "soap " ??

Dish washing liquid ( for hand washing) has no alkali, rinses off completely, is non-conductive, non corrosive to bare metals and hence safe for use with electronics.

OTOH, products sold for washing clothes and for use in dish washing machines generally contain alkalis, the water solution is conductive, corrodes bare metal and is hard to fully rinse off.

Dish washing liquid is the only one that is proven safe to use.

Liquid hand wash ( soap free & pH balanced ) is probably OK too.

Use any others at your peril.

.... Phil

Reply to
Phil Allison

I prefer to use mild solvents actually, like alcohol/acetone. This is mainly for PCBs though, when it comes to cabinetry and shit I dunno, dish soap seems really good.

Reply to
jurb6006

** Acetone sure is NOT mild !!!
** Neither is any good for removing oils, grime or drink spills that contain sugars or fats from PCBs.
** Dishwashing liquid is ideal for cleaning PCBs of nearly anything - except non water soluble flux.

... Phil

Reply to
Phil Allison

I have my doubts about anything that has pH Balanced on the label. The term is completely meaningless and is mostly a marketing buzzword. What is the pH of the soap being balanced against? What benefit does this alleged balancing act have for the user? Too many unanswered questions. The best example is pH balanced shampoo. What it does is suds only over a very narrow range of pH. I don't recall the numbers, but it specifically avoids the typically pH=5.5 of skin so that it does *NOT* suds when first applied. Only after dilution with water, or a 2nd application does the pH of the mix increase to roughly a neutral pH=7, where it will produce suds. The obvious result is that users use twice as much shampoo as they would with one that would suds at any pH value. I suspect that hand and dishwashing soap may be similar, but I haven't bothered to check.

Incidentally, the shampoo business gets extra credit for making the bottle caps the same color as the shampoo, so that the user can't easily see how much shampoo they are "measuring" into the cap. Also, by increasing the surface tension, and designing the dispenser orifice so that the first drop comes out as a huge blob of shampoo, which also promoted un-necessary consumption.

As for cleaning a dirty TEK 545, I would use an air hose to evict the dirt and spiders. Then some 409 and a tooth brush on the really grimy spots. Leave the rest alone as I assume that all the electrolytics are bad and that it will need disassembly to replace those anyway.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

Says it right on there if you look at the picture. IIRC the rule is to go b y the marking on the unit if it differs from the manual.

I don't see a 6.25 amp as too big for that thing, I believe that is a body builder model with two handles and probably as many tubes as a 1950s color TV set. They pulled over 300 watts, alot of them almost 400.

I believe that scope is more than 50 tears old, I would say circa 1957. Eve n without transistors they did get a bit more efficient over the years. My old 561A doesn't pull as much as that dinosaur, and I think the only solid state in the is the rectifiers. not sure. but after some years tubes (valve s) wound up with more gain so less of them were needed.

The OP should just put a damn seven amp fuse in it and try it. It does not have a fissionable material in it nor any explosives. If you are paranoid k eep it away from the drapes, or hell just do it outside. Respect electriciy yes, but put it in perspective.

If it blows the fuse immediately the first thing is to disconnect all the r ectifiers off the secondaries of the transformer to see if that's good. In fact if it powers up and has no trace it could still be the transformer. My 561A has leakage to the filament winding which shorts out the HV. I took a hi-pot little 6.3 volt transformer and wired it in, it works fine. However once insulation is breached.......... The nice thing now though is that th e HV is no longer applied to that winding.

I remember that Tekronix had a lifetime warranty on their power transformer s. I tried to get a replacement for mine and they would sell it to me but t hat is all. It's not like they didn''t have them. They basically said that they are no longer under the lifetime warranty. The rep also mention that t hey had alreacy been to court about it, it was like $150 or go f*ck off.

Maybe I should look at a Gould next.

Reply to
jurb6006

**Don't be too certain. My second CRO was an Hitachi copy of the Tek 545A. It was a massive, heavy, noisy, hot bugger. So close, was the copy, that the Tektronix service manual was perfectly suitable for fault-finding and operational needs. FWIW, the only major difference between the Hitachi and the Tek was Hitachi's use of 2% tolerance resistors throughout the entire CRO (except for high precision areas). Tek used 10% or 20% tolerance resistors throughout. The thing used a full RLC delay line with 20 or so valves. The vertical amplifier valve filaments operated in a series string of (as I best recall) 120 Volts DC. Regulation for various circuits (including heaters) was via 3 X 6080 dual triodes. The thing ate them. It had a 200mm fan in the back and consumed 500 Watts under normal operation. Great in the workshop during Winter. Not so good during Summer. My subsequent CRO was all solid state.

A 6.3AT fuse, for 117VAC is within possibility. I've got a manual for it somewhere. BAMA probably have it for free download if you're interested.

--
Trevor Wilson www.rageaudio.com.au
Reply to
Trevor Wilson

basement for god knows how long, and I thought it would be cool to see if it worked. well, it doesn't. It's missing it's fuse and fusecap, and it's power cable. I had read in a couple of places that the fuse only affected the high voltage stuff, like the CRT. I might be totally wrong about this, which is why I'm asking you guys :) Well, with that in mind, I found a newer power cable that seemed to fit the bill, so I tried using that. Nothing. I then tried using a voltage regulator. Still nothing. Now, I'm not sure if it's because of the mysterious missing fuse, or if something else has gone bad inside, or if it was the power cable (which I doubt). My next guess was that it was the missing fuse. Holy crap does this thing have a strange fuse. I've looked all over for something with a similar rating and size, but with no luck. I'm not as worried about the fusecap. I searched for a couple weeks online, but I eve ntually came to the conclusion that the thing would probably never work. Today though, I thought I'd give it a go again.

found a pdf of its manual (which has slightly more info about the missing fuse). Now I think I got in over my head, because I'm too scared to touch anything. Before I go fiddling with 50 year old electrical components, I want to know if it works or not, what I can do to fix the fuse situation (even if only temporarily), and if I should check for anything else.

need some help (obviously, hehe...)

**I had one of these more than 30 years ago. It was hot, noisy, heavy and an average performer. Do yourself a favour - buy a newer CRO. Even something as old as a Tek 565b will be a revelation. You'll even be able to move it about, without a forklift.
--
Trevor Wilson www.rageaudio.com.au
Reply to
Trevor Wilson

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