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Re: Powering up after long storage
Dave Seiter
I agree with Chuck's comment; I've always just checked for anything wonky, cleaned anything that looked questionable, and turned them on. I would never use a variac on anything with a switching PS. My experience with tube gear is that it either works or it doesn't; a variac wouldn't have made any difference.
When I got my initial 2 pallets of Tek gear, I was going to build a test load so I could work on all the ticking 7704A PSUs, but I never got around to it. Most of the problems turned out to be Ta caps in the mainframes. -Dave From: "stingray666@rocketmail.com [TekScopes]" <TekScopes@yahoogroups.com> To: TekScopes@yahoogroups.com Sent: Sunday, August 6, 2017 9:25 AM Subject: Re: [TekScopes] Powering up after long storage Well, I'm suitably flabbergasted by this comment. I'd been given to understand one had to slowly wind up the supply voltage on the variac whilst monitoring the current drawn by the oscilloscope, keeping that current down to below 100mA at the outset and monitoring for it falling slowly back as the caps 'healed' up whereupon it would be safe to increment the supply volts again. And so on. Now you say this is worse than just plugging the thing in and giving it full voltage from the get-go. Would it be any better to isolate the PSU section of the scope, place it under a dummy load and then going through the above process secure in the knowledge that the rest of the instrument will not be damaged? 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Re: WTB: Tek 475 Spares - (UK)
Rob Angell
Hi All,
Just a quick note to say; many thanks to everyone who responded; either directly, or via the list, much appreciated. A kind list member is packaging up some spares for me, so hopefully my 475 will live another day. All the best, Rob Angell.
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Re: Powering up after long storage
Paul B.
Well, I'm suitably flabbergasted by this comment. I'd been given to understand one had to slowly wind up the supply voltage on the variac whilst monitoring the current drawn by the oscilloscope, keeping that current down to below 100mA at the outset and monitoring for it falling slowly back as the caps 'healed' up whereupon it would be safe to increment the supply volts again. And so on.
Now you say this is worse than just plugging the thing in and giving it full voltage from the get-go. Would it be any better to isolate the PSU section of the scope, place it under a dummy load and then going through the above process secure in the knowledge that the rest of the instrument will not be damaged?
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Re: Powering up after long storage
Chuck Harris
Actually, most of those that know, know that isn't
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the case. Variacs won't help. They are frequently fatal when applied to switching power supplies, or scope supplies with time delay relays... Failed electrolytics will get hot, but rarely will they blow up right away. There is usually time for you to evaluate their condition as part of the after you turn the scope on ritual of checking power supplies for correct voltage and ripple. Variacs to reform electrolytics, won't. They have too low of an impedance, and as such, the minor shorts that happen as the oxide layer takes its two steps forward and one step back journey while reforming, will simply get blown away and damage the capacitor. Reforming requires serious current limitation to work effectively. Check the scope for stray parts, bugs, missing parts, physical abuse, plug it in, and turn it on. Measure the power supply voltages, check their ripple, and then turn it off and check the filter caps for heating. Be mindful that electrolytic cap's cases are sometimes electrically hot wrt ground. That is about the best you can do. -Chuck Harris stingray666@rocketmail.com [TekScopes] wrote:
Hi all, I believe most people know that if you power an old scope up that's been
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Powering up after long storage
Paul B.
Hi all,
I believe most people know that if you power an old scope up that's been lying around for years doing nothing, then you can expect a *bang* and lots of smoke, usually from an electrolytic that was caught having a nap. Is there a generally agreed procedure for bringing an old scope back to life safely and if so, what is it? I've used a variac in the past but still ran into trouble at times, probably because I wound it back up too quickly. Any tips? Thanks!
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Re: 2230 numerical readout error and power supply noise
On 04 Aug 2017 23:52:19 +0000, you wrote:
But the readout of volt/div is wrong on some settings; always going to the next higher reading according to the analog voltage level supplied by the voltage divider. In other words 2mV/div almost always reads .2V/div which is the next higher voltage range the divider provides to the digital section. 2mV measures 2.267V (which is within the proper range 2.104 to 2.340) but the readout displays .2V (which is the next range 2.340 to 2.502).Does it do this on both channels? Is it only the volt/div readout which is affected? Then I scoped the switch output and found a 20ish KHz spike very noisy about 20mV. My theory now is this spike is fooling the digital decoding. Yes?20kHz is from the inverter. The 100V supply has a 250mV spike. 30V supply a 50mV spike. I replaced both filter caps (C954 and C956) with no change. The 8.6V supply a 30mV and the 5V supply a 20mV. Replacing caps made no difference.I do not think the connection between the readout divider and the multiplexor could cause it to read high but the multiplexor itself could have failed. The 2230 uses 4051 CMOS multiplexors shown on schematic 19 and I have noticed before that they seem to have more reliability problems. There is a +5 volt reference marked +5VREFa, +5VREFb, and +5VREFc depending on where it is used for which the origin is shown on schematic 21. This should be checked for accuracy. If you have done that much work on the power supply, then I would change the rest of its aluminum electrolytic capacitors. They are certainly all worn out.
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Re: S52 pulse head standalone wiring/trigger? S4 for sale.
Tektronix made the Type 285 power supply for operating a single S-50
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series head. The manual includes details and schematic: <http://w140.com/tekwiki/wiki/285>
On 04 Aug 2017 23:28:32 +0000, you wrote:
Hi All:
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Re: Lots of corrosion on my new (newly aquired) Type 576 Curve Tracer
Chuck Harris
The 5V filter is something like 11Kuf, and it dries out,
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letting the 5V logic signals dance wildly. This will affect most everything in the curve tracer. The 3uf 150V, C719, is parth of the -75V regulator's frequency compensation, and it can cause all of the voltages to dance about if it is going bad. Mostly however, it likes to leak sulfuric acid onto the board. It is essential that it be a very low leakage capacitor, or it will cause the voltages to drift. I replace them with a 3uF 200V mylar. It is way too big, so with some creative lead bending, you can fit it under the LV regulator board using the same holes as the original. A little lead insulation is in order. -Chuck Harris Brent Watson brentleew2003@yahoo.com [TekScopes] wrote:
Thanks Chuck,I'll plan to change them immediately I don't suppose they could cause
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576 Curve Tracer no Steps
brentleew2003@...
There are two 2000uf caps in the rectifier circuit for the 50v supply, this is where I found a damaged diode from corrosion. They are in parallel and rated at 75v. I want to replace them with a single 4700uf 100v cap. Is there a reason they used two caps here. Space perhaps. Is this slight over-rating acceptable? It's within the tolerance given in the parts list.+75 -10% I would leave the old caps in place and fit these below where there is space, as removing the originals looks to be rather intensive and risky.
Cheers, Brent
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Re: New 547 owner
Adrian Nicol
Indeed - especially when one has the bad habit of reading threads from the latest post backwards....................!
On Saturday, August 5, 2017 6:10 PM, "'Craig Sawyers' c.sawyers@tech-enterprise.com [TekScopes]" <TekScopes@yahoogroups.com> wrote: >Tek used to offer plastic slip-on covers; you could also use condoms.Now there is a sentence you could take several ways ;-) Craig #yiv7198230673 #yiv7198230673 -- #yiv7198230673ygrp-mkp {border:1px solid #d8d8d8;font-family:Arial;margin:10px 0;padding:0 10px;}#yiv7198230673 #yiv7198230673ygrp-mkp hr {border:1px solid #d8d8d8;}#yiv7198230673 #yiv7198230673ygrp-mkp #yiv7198230673hd {color:#628c2a;font-size:85%;font-weight:700;line-height:122%;margin:10px 0;}#yiv7198230673 #yiv7198230673ygrp-mkp #yiv7198230673ads {margin-bottom:10px;}#yiv7198230673 #yiv7198230673ygrp-mkp .yiv7198230673ad {padding:0 0;}#yiv7198230673 #yiv7198230673ygrp-mkp .yiv7198230673ad p {margin:0;}#yiv7198230673 #yiv7198230673ygrp-mkp .yiv7198230673ad a {color:#0000ff;text-decoration:none;}#yiv7198230673 #yiv7198230673ygrp-sponsor #yiv7198230673ygrp-lc {font-family:Arial;}#yiv7198230673 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Re: P6035B Repair
Robert Simpson
Found the problem. One end of the center conductor came loose from its connection on the little compensation board PCB. With careful soldering using a custom tip, I was able to reattach that very tiny wire and now the probe works again.
Bob
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Re: New 547 owner
Craig Sawyers <c.sawyers@...>
Tek used to offer plastic slip-onNow there is a sentence you could take several ways ;-) Craig
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Re: Tektronix 454
Roger Evans
Probably with the switch half way out each pole of the switch is open circuit. Do you have any way of checking Q164 and Q174? You can do basic open circuit and short circuit checks with just a multimeter.
Roger
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Re: New 547 owner
There is a writeup on the washing process; look on the Vintage Tek web site, or on Stan Griffiths' site.Avoid spraying any cardboard, chassis-mounted electrolytic caps.Tek used to offer plastic slip-on covers; you could also use condoms.Avoid spraying adjustment pots; Tek had covers for those too.Let it dry for several days after blowing out as much water as you can before turning it on.
HankC, Boston WA1HOS [Non-text portions of this message have been removed]
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Re: Lots of corrosion on my new (newly aquired) Type 576 Curve Tracer
Brent Watson <brentleew2003@...>
Thanks Chuck,I'll plan to change them immediately
toggle quoted messageShow quoted text
I don't suppose they could cause the step inop. Brent
On Friday, August 4, 2017, 9:14:29 PM PDT, Chuck Harris cfharris@erols.com [TekScopes] <TekScopes@yahoogroups.com> wrote:
Before you go too far, there are two capacitors that are always bad in the 576. The 5V filter cap, and a 3uf 150V wet tantalum cap. -Chuck Harris Brent Watson brentleew2003@yahoo.com [TekScopes] wrote:
[Non-text portions of this message have been removed]
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Re: Lots of corrosion on my new (newly aquired) Type 576 Curve Tracer
Chuck Harris
Before you go too far, there are two capacitors
toggle quoted messageShow quoted text
that are always bad in the 576. The 5V filter cap, and a 3uf 150V wet tantalum cap. -Chuck Harris Brent Watson brentleew2003@yahoo.com [TekScopes] wrote:
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Re: Tektronix 454
erik erickson
Also just found out trace appears if I leave invert switch halfway out but no functions work when the trace appears.
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Sent from my iPhone
On Aug 4, 2017, at 6:18 AM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:
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Re: Tektronix 454
erik erickson
I just checked the invert switch and when I pull it the trace flashes on the screen and then disappears instantly.
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Sent from my iPhone
On Aug 4, 2017, at 6:18 AM, David davidwhess@gmail.com [TekScopes] <TekScopes@yahoogroups.com> wrote:
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Re: Lots of corrosion on my new (newly aquired) Type 576 Curve Tracer
Brent Watson <brentleew2003@...>
After a day of cleaning and lubing switches and contacts on the 576, it's not as bad as I thought. I used a small artists' brush and lightly coated a few circuit board traces with DeOxit. Using De-ox on all the controls made a big difference. I was able to go through the familiarization procedure up to #51 with optimum results.Replaced a few rusted screws and went through initial test-set up to #51 with optimum results.
Step 47 is the Step Generator. After inserting an NPN transistor and getting a minimum step amplitude, I can't get any steps. I believe I saw some briefly yesterday, but can't get anything today. I got as far as putting my meter on step generator IC U75 pins 9,1,3,5, which respond to the "Number of Steps" switch. But have not been able to follow the path further. I was hoping there might be someone here who knows these well enough to suggest where to suspect a problem. adapter doesn't support it, but didn't think it . I'm using an 013-069 adapter because that's what I have. Here's a short video showing the issue. https://www.youtube.com/watch?v=FdC9qWejY2M&feature=youtu.be Cheers, Brent On Thursday, August 3, 2017, 12:29:15 AM PDT, 'Craig Sawyers' c.sawyers@tech-enterprise.com [TekScopes] <TekScopes@yahoogroups.com> wrote: Mosyt instability is due tovoltages and ripple.like you strip the knobs and pull the front off.The push button switches are notorious on the 576 and other instruments on which they are used. I was lucky enough to get a 576 free from a guy who worked in the BBC Technical Centre in the UK. It had a characteristic problem with the older 576 of epoxy potting on the HT transformer (yours is a late instrument after Tek had gone across to silicone potting, so you're OK there). The BBC were going to put it in the skip, so this guy hauled it home intending to fix it, never got around to it and gifted it to me. Anyhow, to cut a long story short, this 576 had had a really nice life in a dry air conditioned environment. But the push switches were all intermittent. To get to one set, you have to take out all some, or all horizontal and vertical boards. You have to take the knobs off these and undo the switch securing nuts, then a screw at the back. You have to unplug a great number of wires (use your phone to take lots of close up photos so you can put them back correctly). If you have the manual there are clear diagrams which show which colour wires go where too. Once you get them out, you will see a board with the offending switches on it. Using the flexible nozzle on a deoxit can you get a good squirt down the inside of each switch. Exercise each one a lot, then a final squirt. Reassemble. Good luck - these curve tracers are well worth saving! Craig
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Re: 2465A Filter, Implode shield, gray knob
mosaicmerc
Ok, will compare it to my 2465a shield for dimensions.
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