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Re: Tek 475.
Chuck Harris
All of this will be spelled out on the power distribution
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schematic for the A9 board... it's somewhere in the manual. In the meantime, take out the 10 ohm 1/4W resistor (AKA: fuse) and replace it with a new one, and take out the 10uf Tantalum cap and replace it with a new one of higher voltage. You can use an aluminum electrolytic of at least 2x the capacitance, if you want, but the scope's low temperature operation will be compromised... it is not at all certain that you care. I bet the scope works if you do that. -Chuck Harris James R. Bartlett wrote: Hi Michael, |
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Re: Need Help Troubleshooting Tektronix PS280
Chuck Harris
Dave,
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I apologize for trying to help. I like to be abused, it's why I am here. This has been going on for too long, you seemed to be thrashing about getting nowhere, so I thought I could help you. My mistake. When you replaced all of the capacitors (really bad idea), did you put the two series 4.7uf 50V caps back in the right way? The schematic shows them as series aiding, which is wrong. They should be in series bucking (C1141 and C1142). Their purpose is to cheaply simulate a NP cap... I already explained why these supplies go bad, but to recap: They are built from garbage. The design is fair, but the execution is really, really, bad. That there are, to quote you, "tons of bad ones on ebay" should be giving you a clue... think hard, it will come through... If you fix the deficiencies, the design can be reliable, but you have a host of problems to go after... ranging from using weak lead free solder on a board whose holes were sized for the much stronger 63/37 tin/lead solder, to using unsupported solid wire, to capacitors and resistors that are only just marginally so. Nobody can make a killing fixing GW supplies... the only profit to be had is in selling bad ones that you got for scrap prices. Buying new is less costly than the labor to fix a used supply. The only GW supplies that I will repair are those that I get for free, and those that I fix for free for my friends. In spite of it all, you qualify for that service. Nobody wants them repaired if it costs money. I use one or two of the fixed freebies that I kept for the glorious task of charging batteries. The others I gave away... you can't sell them, and you sure can't keep them all. Unlike HP/Harrison supplies, the GW supplies survive battery charging without adding a series diode. -Chuck Harris daven9ooq via Groups.Io wrote: Hi Chuck , I guess you came in on the middle of this , I suggest you read my old posts before you comment, one of my early post is the very first thing I did was recap the two variable supplies they are nearly identical, the slave side has an extra trimmer, no the relays are not motorboating it is dependent on where the voltage pot is , please do not jump to conclusions, I know you better than this! |
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Re: Tek 475.
Hi Michael,
Thanks for the reply. My query was not about R956 but the one to the left of it and is situated in the middle between VR956 and R956, on my PCB component layout most components are identified but not this resistorThat is the one that measures 10 ohms.Seems to go back to C1448 a 10uf Tant Measuring across C1448 I also get 10 ohms.So need to find out where it goes and its component number. I am a patient man and wil keep trying. Thanks again Regards Jim On Thu, 29 Aug 2019 at 15:40, Michael W. Lynch via Groups.Io <mlynch003= [email protected]> wrote: Jim, |
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old 7633, 7613 CRT salvage
John Griessen
Is the gold on the inside of the ceramic envelope thick enough to bother sending to a gold refiner?
Seems similar to extracting platinum from catalytic converters, so I wonder? They were from the per 1972 times when gold was laid on the pcbs thickly... What is a good way to strip soldermask to expose the gold for acid to get at? NaOH comes to mind but... I would not want to dissolve a bunch of lead/tin/copper, then put it on the ground... I just want to send all that to the processor as "plated copper" + solder + FR4. |
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Re: Tek 475.
Jim,
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Gotta Love that magic smoke!? I don't think that is a filter resistor as described in Chuck's last reply, as I do not see a Tantalum cap adjacent to the resistor in that part of the circuit.? R956 is the current limiting resistor for the base of Q956 which appears to be part of the sweep generator circuitry.? In the schematic, R956 is specified as a 10K, 1/4W 5%? resistor, NOT 10 ohms, so if you are seeing only 10 ohms, that is a problem.?? What I would also suggest is to check Q956, plus CR952,CR955, CR956 and VR956 and verify that these components are all good.? Chuck's advice about Tantalum Caps is spot on and you should check the entire machine for blown or otherwise defective caps.? My brother calls them "devil caps", they are prone to failure at any moment.? Michael Lynch?479-226-0126 Home Phone479-477-1115 Cell Phonemlynch001@[email protected]@... On Thursday, August 29, 2019, 6:55:39 AM CDT, James R. Bartlett <james.r.bart@...> wrote:
Hello to the group. I find that I am in need of your assistance. Firsty repairing scopes is not my forte but I want to do and learn. I have a Tek 475, which was working. However I went to use it the other day and got the magic smoke. Problem seems to be related to the +15 supply/ Scope switches on, The smoke came fro a resistor on the A9 board. However it does not appear to be numbered on the PCB layout as shown on the downloaded service manual. It is located to the left and between VR956 and R956 it meters out at 10 ohms Is this the correct value ? and what is its circuit number ? I checked C1448 and that meters out also at 10 ohms. + 15 volt supply is 0 Volt Any thoughts suggestions appreciated . Many thanks Jim |
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Re: Need Help Troubleshooting Tektronix PS280
daven9ooq
Hi Chuck , I guess you came in on the middle of this , I suggest you read my old posts before you comment, one of my early post is the very first thing I did was recap the two variable supplies they are nearly identical, the slave side has an extra trimmer, no the relays are not motorboating it is dependent on where the voltage pot is , please do not jump to conclusions, I know you better than this!?
The fixed 5 volt was ok so did not recap it.? The 5 volt regulator uses A LM 723as a reference,? a little different than the 2 variable sides , Yes it would be nice if one side was working , but no they were both out from the beginning. Another thing to consider is if this supply is so simple as you say why are there tons of bad ones on ebay, a guy like you could clean up and make a fortune fixing them and putting them back in service? That is why I asked the group , how Reliable they were.? Larry has 2 working same revision as mine and said they were pretty reliable, I'll accept this answer , until I know better.??Actually the 470uf electrolytics ESR wasn't that bad , but since I'm working one handed and themain board was so difficult to get out, I changed them all, using New Nichicon? , that was nearly a month ago, and the first thing I did! I found the esr on the smaller electrolytics? to be worse than the larger value ones, the 4- 4.7 uf 50 volt were the worst @ 1ohm and the 47uf were bad too. The rest seemed to be acceptable but were changed? for reliability sake. At this point I'm up to the? references on both sides including the 7815's everything is is good on the +and - 15volts aU 101,Q101,and Q102,from here on is where Ineed help understanding whats going on. John was kind enough to help, when You, Chuck chimed in again, So I am waiting on John to reply back and see if he is willing to walk me through the rest of the way, I am also studying the Theroy of Operation in the manual on Tekwiki even though it's a different revision, I believe all revision's share the same circuitry ,the only difference is the number of circuit boards, earlier ones had a seperate fuse board and all the jumpers and connectors are labeled differently and the looks and heatsink. If John is willing to accept my terms of working at my own pace and time, We can proceed when I am able to in about a week or so,?Chuck please Let John lead the Thread and if you have something to add, than go from there. I have to pick up my stepson tonight , and we have plans until after the labor day weekend? my wife Esther is off all next week so I probably won't be able to do much? until after that John if your willing you can talk me through the rest of the way now, if not maybe Chuck can take over if he is willing and I will try to study up on? the Theroy and will report back , when able. Many Thanks guys! Dave |
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Re: Tek 475.
Chuck Harris
Not looking at the schematic, but tek scopes of that era
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are littered with filters for the power entering the boards, that are made from 10 ohm resistors with a tantalum capacitor to ground. Use your eyes and look for the capacitor, or remains of the capacitor, that is near the resistor. It will usually be of the tantalum drop variety, with color bands. Sometimes, they blow up, leaving just two leads sticking out of the board where the capacitor used to be. Other times, you will see what looks like a three leaded capacitor.. And still other times, the capacitor will look normal, but be a dead (0 ohms) short. When you replace it, pick a tantalum value that is at least twice the operating voltage of the power it is filtering. If it is on the 15V supply, use a 30V tantalum capacitor. -Chuck Harris James R. Bartlett wrote: Hello to the group. |
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Tek 475.
Hello to the group.
I find that I am in need of your assistance. Firsty repairing scopes is not my forte but I want to do and learn. I have a Tek 475, which was working. However I went to use it the other day and got the magic smoke. Problem seems to be related to the +15 supply/ Scope switches on, The smoke came fro a resistor on the A9 board. However it does not appear to be numbered on the PCB layout as shown on the downloaded service manual. It is located to the left and between VR956 and R956 it meters out at 10 ohms Is this the correct value ? and what is its circuit number ? I checked C1448 and that meters out also at 10 ohms. + 15 volt supply is 0 Volt Any thoughts suggestions appreciated . Many thanks Jim |
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Re: Tek 576 Curve Tracer HV Transformer winding
Chuck Harris
I'm not particularly worried about the water picking up
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anything too bad... a few parts per million lead, maybe some PFOA's. I only mentioned it because businesses that don't worry can be fined heavily by their local EPA. I am more concerned about ease of use. The water makes the whole process more likely to cause burns. Hot air in an oven gets you to the same place with no more risk of burns than handling a tin of hot muffins with an oven mit. As I've said earlier, I have done this hundreds of times. IMHO, hot air in a 130C (266F) oven for 1/2 hour works best... -Chuck Harris Andre de guerin via Groups.Io wrote: Hi, yes have also used the hot water method. |
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Re: Tek 576 Curve Tracer HV Transformer winding
Hi, yes have also used the hot water method.
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Incidentally its best to test this on a failed transformer of the same time first to get the technique right.I also have used a very small amount IPA to release stubborn windings, this shouldn't damage them butif you use anything else be aware that winding damage is likely.If you're worried about the risks simply do what I did and use the water to make Plaster of Paris. -Andre #include "802701.h" On Wednesday, 28 August 2019, 18:12:23 BST, Chuck Harris <cfharris@...> wrote:
The only reasons I use an oven over the water technique (aka teacup method) for a couple of simple reasons: 1) it seems less likely to burn me.? Water soaks ? through my leather gloves, and it gets hot quickly. 2) Businesses have strict rules about what they can ? dump down the sink.? Since they would have to prove ? that the water carried nothing dangerous, I prefer ? to avoid the issue... and use air. -Chuck Harris Miguel Work wrote: Thanks Chuck! |
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Re: Thoughts on TDS744A
I have a couple of 744As that I converted to 784As by removing the bypass caps across the vertical amp outputs and moving the zero-ohm jumpers according to the instructions widely available on the web. NB there's some bad info out there regarding the jumpers--do it wrong and you'll have the 1-GS/s "export model" instead of the 4-GS/s US model. Fortunately nothing breaks if you do it wrong--you just have to switch jumpers again.
Those 784As are my general purpose bench scopes, and have been for 6-7 years. Highly recommended, especially at $350. From a UI point of view, the main issue with the TDS 7xx series vs. the TDS 6xx is that the knob response is sluggish at slow scan speeds. It feels as though the knob inputs are only applied when the current acquisition is completed, whereas the 6xx scopes register it right away. My TDS 694C definitely has better knob response. Cheers Phil Hobbs |
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Re: TDS 694C CRT screech
I installed one of the NewScope kits on a TDS 784A, and it's very pretty. My 694C has a beautiful bright display still--it's a Frankenscope cobbled together from an early unit that was used internally at Tek for testing, plus a brand new display section and front panel, so it would be sort of nice to save it. If I don't get other good leads, I'll probably do as you suggest. (I have a second NewScope kit on the shelf waiting to be used on my other 784A, but a mildly dim display is a lot less objectionable than that screech, so I could probably repurpose it.)
Thanks Phil Hobbs |
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Re: OT- question relating to DC shunt motor schematics
Send it to me off list, I will help you all I can. Bruce
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On 8/28/19 11:28 PM, Dave Seiter wrote:
Hi Bruce, thanks for the input! |
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Re: OT- question relating to DC shunt motor schematics
Chuck Harris
It really doesn't matter. Because both the field, and the
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armature change polarity, when you change supply polarity, the motor will continue to spin the same direction. Back in the days of yor, when there were competing AC and DC power generation systems, a universal motor was imagined, that would run on either AC or DC equally well. It is just a DC motor with the field and armature in series or shunt. To reverse a series, or shunt motor, you have to swap the field connections relative to the armature connections. -Chuck Harris Dave Seiter wrote: On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter". |
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Re: OT- question relating to DC shunt motor schematics
Hi Bruce, thanks for the input!
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If I sent you a photo of the schematic off list, could you make an educated guess (or perhaps see something I've missed?).? I've read schematics since my Radio Shack 101 kit, but power control, especially 3PH, is all new to me.? Vintage makes it even more interesting.?? Regards, -Dave On Wednesday, August 28, 2019, 07:57:58 PM PDT, greenboxmaven via Groups.Io <ka2ivy@...> wrote:
In my 30 plus years in the elevator craft, I have never seen or heard of any standard of L1 and L2, and I have worked on many DC motor starter/reverser panels. Different manufacturers used whatever designation they wanted to, every print I ever saw made it clear which? input terminal was to be positive and which was negative. Polarity is very important, large contactors have "blowout" coils or magnets, improper polarity can prevent the arc formed when a contact opens from being snuffed.? A flashover between contacts is a sensory experience you will not forget! It is great to hear someone discussing old control gear, learning about it is vital for proficiency with newer controls, and there is a surprising amount of that gear still in use today. ? ? ? Bruce Gentry, KA2IVY International Union of Elevator Constructors, Local 62, Retired On 8/28/19 10:03 PM, Dave Seiter wrote: On the schematics pertaining to DC shunt/series motor starters, is there any naming convention relating to L1 and L2 being positive/negative?? I ask because I'm used to DC systems specifying polarity, and the only "polarity" mentioned on the schematic I have is the name "D.C. Automatic Starter". |
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Re: TDS 694C CRT screech
My favourite scope, a TDS 694C, has developed a nasty screeching sound when The downside is that you may feel compelled to kick yourself for not ditching the CRT earlier. Also, no more trippy head spinning when your gaze accidentally sweeps past the color shutter! -- john, KE5FX |
Jason A.
Michael W. Lynch
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