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Re: 7904 Mainframe damaged
Your isolation transformer should be grounded. And pass the safety ground through to the UUT.
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What should happen is the connection between the Neutral and the Ground must be broken. This connection is made back at your service entry panel. With that condition removed, it should not matter if you place a ground on either the Line or the Neutral on the secondary of the isolation transformer. This is no different than the old transformer based power system. Maybe you can find a working 7904 power supply somewhere. There were many of those scopes made. Does the power supply make a ticking sound when power is applied? Any visible signs of blown parts in the supply? Do you have continuity through the RFI filter on the scope? You might say where you are located case someone is near you that can help. Regards ----- Original Message -----
From: "JJ" <jajustin@...> To: <[email protected]> Sent: Friday, April 06, 2018 4:23 PM Subject: [TekScopes] 7904 Mainframe damaged Hello, I own a beautiful 7904 scope that I damaged when probing a stereo receiver. I didn't realize that my isolation transformer was earth grounded - forgot to remove the ground strap. So I effectively shorted out the scope by touching the probe's ground lead to a voltage node. The mainframe (without any plugins installed) doesn't power up. When the event happened, the scope remained on. But, after shutting it off, it wouldn't come back on. There's no activity - just dead. I checked the fuse but I knew that wasn't going to be the problem since the surge came over the ground. I have the service manual. I was just wondering if there was an obvious place to start looking since this could have happened to others. I'm hoping that it's repairable - my heart is broken. I've used this scope for over 40 years. I'm a retired 70 year old electronics engineer. I guess I'm just getting old! |
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Re: 7904 Mainframe damaged
Chuck Harris
You don't say where in the world you are, so I have
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no insight into whether you are in 120V land, or 240V land, but.... There really isn't any place on a 7904, or its usual plugins where you could stuff the power line current into that would destroy anything more than the bench's fuse, or one of the scope's ground leads... particularly the probe's. If you are a retired electronics engineer, put you hat back on for a few minutes, and draw some sketches of how the isolation transformer, and the stereo's guts could force current into each other with what you did when you saw the flash. I think you will come to agree with me that the only two parts of your 7904 that are at risk are the scope probe's ground wire, and the green (bond) wire on the scope's power cord. All of the 1M vertical amplifier inputs are safe to 300V, as are most every other input in the scope. The 50 ohm vertical amplifiers will blow, but the damage is limited to the plugin. 7904's are notorious for eating up tantalum electrolytics on the +/- 15V filters on various PC boards, and plugins, and the +50V filters on the CRT amplifier cards. They blow when you look at them cross-eyed, or don't... when the wind blows, or doesn't. 7904's are notorious for having a power supply that is extremely sensitive to overload, and as such protects itself from just about any insult you could hurl at it. The second part of my diatribe has to do with isolation transformers, and why you were using one. First, your scope's measurement ground is directly connected to your scope's case, is directly connected to the bond wire on the third pin on the power cord. As a result, it is never safe to use an isolation transformer to break that bond wire, and float your scope... I hope you weren't doing that! Second, it is rarely necessary to use one for anything other than switching power supply work on a DUT. What were you expecting the isolation transformer to isolate? -Chuck Harris JJ wrote: Hello, I own a beautiful 7904 scope that I damaged when probing a stereo receiver. I didn't realize that my isolation transformer was earth grounded - forgot to remove the ground strap. So I effectively shorted out the scope by touching the probe's ground lead to a voltage node. The mainframe (without any plugins installed) doesn't power up. When the event happened, the scope remained on. But, after shutting it off, it wouldn't come back on. There's no activity - just dead. |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
I don't know the board in question, but if any "dead spots" in the area to be repaired, try drilling some holes. Any epoxy will do the job if it has something to key into.
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I don't think of epoxies as "glue", but something that gets the fine detail and then goes SOLID. Les. On 06/04/18 19:33, Brian Bloom via Groups.Io wrote:
Hi everyone! |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
Dennis:
Thanks for the idea and the offer! I have a single slot parts plugin with a good end shroud that I could use. I initially checked it to see if it was compatible, saw that it was different, and disregarded it for it's differences without even thinking that I could just take the dremel to it. That seems to me to be a substantially better option than gluing the old one back together and hoping it'll hold. However, there are some note worthy differences to the 7S14 end shroud and the standard plugin end shroud (see pictures). /g/TekScopes/album?id=42544 -As you'll see in IMG_1306, the overall stand-off of the four pointed parts is slightly shorter on a standard plugin. -In IMG_1305, you can see that there's also notches for the metal back-plate to seat inside the shroud (IMG_1307) - easy enough to cut in. -Additionally, the part at the top of the shroud with the four holes is much shorter on a standard plugin. Do you consider any of the above noted points to be (possibly) creating a compatibility issue between the 7S14 shroud and a standard shroud? Of course I'll need to remove it from the spare plugin in order to measure and note any other significant differences before I start hacking away at it. Jeff - As Dennis mentioned, these end shrouds on the 7S14 are presumably not common to any other 7K plugins, so it's doubtful that it would be worth your time to replicate. Also, as long as 7K parts plugins are readily available for cheap, I don't think the standard 7K end shrouds would be worth your effort, either. Then again, I'm just one person, so it may be worth asking others if there's any demand for replicas. Those 100 series rear feet prototypes look good! Nice and strong! As soon as I pull this shroud off of the single-width plugin, I'm going to make some space and pull down the 191 for test fitting and pictures, at which point I'll email you pictures/comments etc. You'll hear from me within the hour! Thanks again! Brian |
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7904 Mainframe damaged
Hello, I own a beautiful 7904 scope that I damaged when probing a stereo receiver. I didn't realize that my isolation transformer was earth grounded - forgot to remove the ground strap. So I effectively shorted out the scope by touching the probe's ground lead to a voltage node. The mainframe (without any plugins installed) doesn't power up. When the event happened, the scope remained on. But, after shutting it off, it wouldn't come back on. There's no activity - just dead.
I checked the fuse but I knew that wasn't going to be the problem since the surge came over the ground. I have the service manual. I was just wondering if there was an obvious place to start looking since this could have happened to others. I'm hoping that it's repairable - my heart is broken. I've used this scope for over 40 years. I'm a retired 70 year old electronics engineer. I guess I'm just getting old! |
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Softening insulation between HV Transformer Windings
I have a HV transformer with 7 windings (14 lugs for connecting to those
windings), and 5 additional lugs for taps on some of the 7 windings. The windings generate various voltages from 5V to 3.5KV. it is used in a simple push pull oscillator with about 96V on the primary. It uses a square ferrite core, and it oscillates probably just above human hearing range (>20KHz). It has a Tek part number 115-0601-00, and the following additional info: SAR 5081 on it. Something happened to one of the middle windings that blew a dime size hole outward causing it to short out one or more of the windings from near that layer all the way to the outer layer where it is plainly visible. I would like to carefully remove what I think is paper between windings but it seems to have been impregnated with something that makes it extremely hard. Is there something I can soak the entire transformer in to soften up this material whatever it is so I can start to "peel this onion" so to speak without destroying the clues that might tell me what went wrong with it in the first place. Dennis Tillman W7PF |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
I would use JB Weld epoxy.
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----- Original Message -----
From: "Brian Bloom via Groups.Io" <analogaddict013@...> To: <[email protected]> Sent: Friday, April 06, 2018 3:38 PM Subject: Re: [TekScopes] Seeking advice: Repair of 7K "circuit card guide" on back of 7S14 On Fri, Apr 6, 2018 at 12:08 pm, Pete Lancashire wrote: Sure thing! /g/TekScopes/album?id=42544 I'm quite confident that it can be mended if the proper adhesive is used. In order to select the correct adhesive, I need to determine what type of plastic these are made of. I have a kit of " Loctite Plastics Bonding System" on hand, which claims to work on all plastics including polyethylene and polypropylene, however it fails to state any tensile strength specs. I do have a spare main interface board with a broken standoff on one card edge connector that I'll go ahead and use as a trial run. |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
Jeff Davis
Brian,
Would you like me to take a shot at modelling / printing these? Jeff P.S. I see that the post office has delivered the 100 series rear feet prototypes. Anxious to hear your thoughts on them. ________________________________ From: [email protected] <[email protected]> on behalf of Brian Bloom via Groups.Io <analogaddict013@...> Sent: Friday, April 6, 2018 1:14 PM To: [email protected] Subject: Re: [TekScopes] Seeking advice: Repair of 7K "circuit card guide" on back of 7S14 If only I had a 3D printer... although it is something that may be worth the effort. The circuit card guides on this double slot module are different from the single slot modules and I assume more rare. Upon further inspection of the Loctite product I have on hand, it's just CA with an activator/primer that smells like the Xylene from old school king size sharpies. I'll still give it a shot on the broken card edge connector standoff on the spare board and see how it holds up. However, the difference in the stress that it would typically see is going to be different from the stresses on the circuit card guide. The only way I'm going to know for sure is to try it on the actual piece and then use the plugin as I normally would to see if it holds up. I'm going to give it some time to see if anyone here has had success with any particular method/product other than replacement before I proceed on the card guide, as I don't want to make a mess of it or make it impossible to mend due to contamination. |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
Please excuse my ignorance, but what's "CA"?If I'm correct in my interpretation: CA = Cyanoacrylate aka superglue @Shaun: Thanks! Funny enough, that's actually the product I was originally looking at using! I'll go ahead and put in the order now. Brian |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
I presume he means _c_yano_a_crylate aka super-glue? I've found they can tend to be fussy about bonding to some other plastics, there are (or were back when I last used them) some that come with a separate little bottle of surface activator which you brush on first, they seemed to work well on difficult plastics.
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Good luck! Adrian On 4/6/2018 9:01 PM, Brad Thompson wrote:
Please excuse my ignorance, but what's "CA"? |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
Hi Brian,
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This looks like the standard end shroud of any 7000 plugin with a small exception which shouldn't be hard to modify. On the 7S14 there are those 4 large holes that special nuts fit into. I'm not sure why Tek made this modified one for the 7S14 but it could be because the 7S14 was one of the first 7000 plugins to come out. I can send you a standard end shroud that I removed from a dead plugin if you have a way to drill those holes in it. It has a tiny piece at the end of one of the pointy card guides missing, but there is so much left that it will still hold the card perfectly in place. You can have it for whatever the shipping charge comes to. Dennis Tillman W7PF -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Brian Bloom via Groups.Io Sent: Friday, April 06, 2018 12:38 PM To: [email protected] Subject: Re: [TekScopes] Seeking advice: Repair of 7K "circuit card guide" on back of 7S14 On Fri, Apr 6, 2018 at 12:08 pm, Pete Lancashire wrote: Sure thing! /g/TekScopes/album?id=42544 I'm quite confident that it can be mended if the proper adhesive is used. In order to select the correct adhesive, I need to determine what type of plastic these are made of. I have a kit of " Loctite Plastics Bonding System" on hand, which claims to work on all plastics including polyethylene and polypropylene, however it fails to state any tensile strength specs. I do have a spare main interface board with a broken standoff on one card edge connector that I'll go ahead and use as a trial run. -- Dennis Tillman W7PF TekScopes Moderator |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
If only I had a 3D printer... although it is something that may be worth the effort. The circuit card guides on this double slot module are different from the single slot modules and I assume more rare.
Upon further inspection of the Loctite product I have on hand, it's just CA with an activator/primer that smells like the Xylene from old school king size sharpies. I'll still give it a shot on the broken card edge connector standoff on the spare board and see how it holds up. However, the difference in the stress that it would typically see is going to be different from the stresses on the circuit card guide. The only way I'm going to know for sure is to try it on the actual piece and then use the plugin as I normally would to see if it holds up. I'm going to give it some time to see if anyone here has had success with any particular method/product other than replacement before I proceed on the card guide, as I don't want to make a mess of it or make it impossible to mend due to contamination. |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
Brad Thompson
On 4/6/2018 3:56 PM, n4buq wrote:
If epoxy doesn't "stick" to it, CA might. I've had instances where that was true.Hello, Barry-- Please excuse my ignorance, but what's "CA"? Thanks, and 73-- Brad AA1IP ...Still searching for a container that'll hold the Universal Solvent.... |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
If epoxy doesn't "stick" to it, CA might. I've had instances where that was true.
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Looks like a good 3D Printing project. Thanks, Barry - N4BUQ ----- Original Message -----
From: "Brian Bloom via Groups.Io" <analogaddict013@...> |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
On Fri, Apr 6, 2018 at 12:08 pm, Pete Lancashire wrote:
Sure thing! /g/TekScopes/album?id=42544 I'm quite confident that it can be mended if the proper adhesive is used. In order to select the correct adhesive, I need to determine what type of plastic these are made of. I have a kit of " Loctite Plastics Bonding System" on hand, which claims to work on all plastics including polyethylene and polypropylene, however it fails to state any tensile strength specs. I do have a spare main interface board with a broken standoff on one card edge connector that I'll go ahead and use as a trial run. |
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Re: Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
How about some pictures
On Fri, Apr 6, 2018, 11:34 AM Brian Bloom via Groups.Io <analogaddict013= [email protected]> wrote: Hi everyone! |
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7L5 repair and calibration
Hi Everybody,
After more than a year of persistent search I finally got myself a 7L5 off US eBay and managed to ship it to the other side of the planet. Decent condition, few scratches, no moisture/corrosion. Seller noted it had a dead digital storage (only classic analog sweep possible, blank screen with storage on), it's an older model (S/N below B07xxxxxx, two PCBs in digital storage instead of one). I remember from somewhere a comment related to 7L analyzers "nice, but can be real bears to repair", and I certainly can second that. It took around ~10h to understand how digital storage works internally and debug it, revealing a dead 4006 (U4070, one section output stuck to logical high). The IC was RCA in a ceramic packaging, nice and clean, always thought these were indestructible. Still high on endorphine from recent success I went to calibrate it, only to discover that attenuator was skipping steps and levels were way off. Another ~4h of debugging revealed a semi-functional (!) 4051 multiplexer (U1450) behaving erratically. Next came the calibration, and since filter responses were poor I decided to do it fully. As the manual already warns, calibration of this instrument literally takes days, and this is true to the word. In addition to that, all coil cores have been fixed by a layer of varnish that over time ate the plastic adjustment screws. Half of these disintegrated into dust as soon as the tool exerted any force on them, so a prosthetic work had to be done to make these adjustable again. But regardless of this, filter adjustments (30kHz and 10kHz, these are classic L-C) proved a real pain. No matter what I did I could not get rid of the annoying bump in the response, both on 10kHz and 30kHz: I would be glad if any of you 7L5 users could comment or share the shapes of your instruments responses. I'd like to calibrate mine properly for noise analysis. Best Regards and thanks, Nenad Filipovic |
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Seeking advice: Repair of 7K "circuit card guide" on back of 7S14
Hi everyone!
I have a 7S14 that has a cracked circuit card guide. The connectors still function and make contact when inserted into the mainframe, but I want to repair it the best I can to prevent further damage without having to deal with the trouble of seeking/buying a replacement at this time. My initial thoughts are to use some high quality epoxy to mend the plastic, but I've experienced failure doing this on other non-related projects. Some epoxies just don't seem to work on some plastics despite the manufacturer's statement that it works on "all plastics". Has anyone else repaired one of these pieces with success? What type of glue or epoxy did you use? -Brian |
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Re: Replacing 453 rectifier tubes.
Here is what I just noticed. Connected to TP 1047 with intensity to minimum I get 4.xx something volts. Increasing intensity to 12V requires almost 3/4 turn of the pot. No voltage change from 4.xxV for the first 3/4 turn. As I said earlier I have swapped pots and the issue remained. The other pot I used is in my other 453 and behaving normally.
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Shaun M
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