Video není dostupné.
Omlouváme se.
Tektronix 485 Restoration, Scope dies on the bench and asks for more help.
Vložit
- čas přidán 9. 03. 2022
- Thank you to all the new subscribers we have had for the channel we greatly appreciate everyone being here. We check the comment sections regularly any input is also greatly appreciated.
Ways to support the channel: / zenwizard_studios
In this video we take a look at the restoration process of a Tektronix 485. This was the fastest scope that Tektronix made in the 485 series at 350 Mhz. This one has some issues in the power supply as well as dies on the bench, and asks for more work. There will be a follow up video on the calibration process. If there is more interest in the 485 I have a second scope in the lab that has the P11 phosphor but I have a parts scope with a potential good tube. I could do a tube swap see. The other unit has the RF shielding option.
** Repair exposes the Tech to mains electric and should only be done by trained personal. Errors can be fatal. **
I can't tell you how many times when working on Tek scopes that the scope shut down with a tantalum cap failure. I just fixed my 485 recently and was calibrating theB trigger when a 22uF 15V cap on the 15V supply went south. Tek was famous for running these caps too close to their limts. About an hour after that cap failure the large 100uF gumdrop cap again on the 15V supply failed with a short. I have never had one of the metal cased glass sealed tantalums fail, only the epoxy cased ones. Fortunately I had a 485 carcass that I squirreled away for parts. So my $10.00 hamfest dead 485 took two transistors, a tunnel diode and two tantalum caps to fix along with some minor calibration tweaks. The only remaining thing to do is to pull the vertical attenuators and get out the 99% IPA and clean the contacts to eliminate a bit of noise and flakiness. I am looking for either a front cover or a 3D print file for one. Nice video series by the way.
Sam W3OHM
Great video, very helpful! Looking forward to the second part
Coming soon!
So a surprise Tantalum cap failure on Vertical Board.
I checked my vertical board and that cap was not shorted but one near it was.
Nice way to test burnt caps with ohmmeter with -0.2 - 0.6 ohm identifying a DUDD cap.
Nice video, as usual! I'm a bit surprised that you replaced all cylindrical caps in the power supply, many of which are hermetically (glass) sealed solid tantalum caps. The latter ones very seldomly break down. You left the many dozens of dipped tants across the boards alone. These are infamous for breaking down these days and actually, your 6.8uF already did. They sometimes literally go up in flames, so I wouldn't leave that 'scope on without supervision, because your intended burn-in may end up a burn-out.
If you plan on using the 485, a lovely 'scope, for years to come without problem, rigorous replacement of all dipped tants is unavoidable, since they become such a common cause of failure after several decades.
I own two 485's, both in an even nicer condition cosmetically than your 485, AFAICS, and I really enjoy using them. BTW, your 485's s/n shows your 'scope was made in Heerenveen in the Netherlands, my home country.
I noticed that as I was doing the recap. I am not going to ditch the glass tantalum as they will be good for a LONG time yet, they will be saved I was actually really surprised to find them in the power supply section. None of the burn ins have been unsupervised, I dont trust it for a while yet. I noticed that it was out of the Heernveen plant. I am sure this unit has a story to tell as to how it ended up in the US. I do plan on having it on the bench and using it as a daily driver when I am in the lab. I have found I need to 50 Ohm input much more often then I realized so it will be nice having it built in.
If another dipped tant goes I will be doing a very aggressive replacement of all of them.
I have 485 in my bench which need to be calibrated .. the a and b sweep are not properly aligned.. they are missed the timing. Looking forward for the detail alignment process.
I am recording the process now. It sounds like you need to do the B register adjustment. I am about 1/2 way through the HORZ alignment now. There will be split videos again the process looks shorter on the calibration instructions but still takes some time.
I have a 485 and I need to replace the fan motor. Does anyone know how the fan is attached to the motor shaft? Is it just a pressed fit or is there something else which needs to released first?
I apologize in advance for my stupid question: Can anyone help me a little. I do not understand the values on the tantalum capacitor that has been replaced, that is, by which color chart it is determined. I am not able to find a suitable one that gives me 35 v for the colors on that capacitor. Thanks...
Not at all, In this case I used the bill of materials (BOM) in the service manual to get the exact value that I needed to be replaced. Using the component map I determined the C(number) and using the "Electrical replacement parts" list in the service manual got the value, voltage, and tolerance. With some Tektronix parts this can be more valuable as some will be listed "selected from" (IE "selected from 2n3904) this means there was a specific parameter that was impotent, that was tested for and binned. This usually happens more with active components than capacitors. But I also check for updates to the BOM some times there will be value changes like an increase in capacitance or voltage as the design became more refined. These are usually called out in the BOM by serial number.
@@ZenwizardStudios Thanks a lot for the reply. How would you determine the value of that capacitor, say you don't have a BOM? Again, I failed to find a color chart that clarified the values on it. I'm sure the problem is my lack of understanding of how to decipher colors the right way ...