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Re: Tek 2225 that wont power up after a knock :-(
The doc I found online was called "troubleshooting_tips_on_2200_ps.pdf" but as I said it talked about Q9070 ...
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Dave On 16/03/2021 22:33, David Slipper wrote:
I looked for that document in the files section but failed to find it :-( |
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Re: Tek 2225 that wont power up after a knock :-(
I looked for that document in the files section but failed to find it :-(
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I even tried search terms like 22xx and supplies. I found a doc on line but that talks about Q9070, a FET which isnt on my schematic. Dave On 16/03/2021 21:26, satbeginner wrote:
Hi Ozan, |
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Re: 485 super weak brightness control
Thanks so much for your reply, it makes it much easier to approach.
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I cleaned up the HV test point and I get now some 2800V. What makes me little bit nervous is I don't know if the cause was just the contact cleaning or if something else have changed. Nevertheless it changed in the right direction. I think the whole section under the plastic cover needs cleaning it's covered in black dust. I will de-solder the diodes in the DC restorer and measure leakage current. The intensity is too bright I'll get back to you when I follow up on the other measurements tomorrow. The HV probe is labeled as HV-40 but can't find any manufacturer markings. It's definitely from 80s or 70s On Tue, 16 Mar 2021, 22:42 Ozan, <ozan_g@...> wrote:
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Re: Corrosion Damage ¨C TM500 Plugins
It could just be galvanic corrosion. The graphite in the conductive foam is at the very top of the galvanic series () and can corrode even noble metals like gold and platinum in the presence of sufficient moisture to enable the reaction.
I have seen very severe corrosion on the pins of ICs placed in this conductive foam when stored in a humid conditions but in an otherwise open enclosure. The corrosion only occurred on the area of the pins in direct contact with the conductive foam. Areas not in direct contact with the foam were completely unaffected so it seems unlikely that there was any gaseous agent causing the corrosion. |
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Re: Corrosion Damage ¨C TM500 Plugins
I guess I am getting a little confused at this time but better understand the situation. Somewhere in there the Tektronix subject changed to HP and storage turned into accessory cases.
Earlier model HP accessory cases were notorious for breakdown of the foam liners. I have witnessed anything from the foam crumbling to dust (as you mentioned) all the way to it turning into a sticky goo that captured the contents and took considerable cleaning to remove with some corrosive effects along the way. The dust aspect seemed to be simply from age and the goo from high humidity conditions. Older Tek portable scopes that had the front accessory covers (453, etc.) were known for either disintegrating dusty foam and/or the fastening material drying out releasing the foam from the cover. The darker open cell foam you indicated in the one web link appears to be a later version product. I have seen it in newer cases and always recognize it from its more darker color and coarser cell size. I order closed cell foam to build up transit cases and have never had any problems using it. But I also order the foam from those sources who also build up custom cases so always feel relatively assured that their products are safe. The downside to it is that they tend to extract high prices for the foam. I¡¯m not certain if you brought the subject into your discussion regarding the TM500 plug-in accessory modules or not but they contain a hard plastic liner and fortunately no foam products (at least to my knowledge given the several I have here in the lab). Either way I am sorry for your discovery. It¡¯s always disheartening to pull out an older piece of hardware and find irreparable damage. I think foam manufacturers are now a little more sensitive to the ingredients in their products and the subsequent damage that can be caused. And if there is any uncertainty about foam in older equipment that still is in relatively good condition it is better to err on the cautious side and replace it if possible. Calls to the foam manufacturers to verify their products is a wise step in assuring that there will be minimal surprises in the future. Greg |
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Re: Tek 2225 that wont power up after a knock :-(
Hi Ozan, David
Sorry for my mix-up, small screen, big fingers, poor lighting. Anyway David, Hakan's document is great. I also repaired several 22XX scopes, in the threads I started about a 2215, 2215A and a 2235A, you can find the link to the document as well. Leo |
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Re: Corrosion Damage ¨C TM500 Plugins
There were some "miracle material" foams and tough flexible plastics used in the 1960s and 70s. Many of them decompose to very vile residues that are often corrosive. One that had? devastating consequences to an industry and cost tens of millions to? remedy was the adaptation of polyurethane sheet that was not made correctly. In many cases, someone eager to embrace a new material would take shortcuts or not do adequate research regarding critical details in the formulation. If this stuff decomposes in a closed environment?? and was blown with hydrochloroflorocarbons, that would add some very corrosive? elements that might become part of the brew. I have cleaned up many items damaged by these residues.
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??? Bruce Gentry, KA2IVY On 3/16/21 14:04, - wrote:
A couple of questions and comments. |
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Re: 485 super weak brightness control
Note that checking the leakage of those diodes is important, just a DVM diode check doesn't discover problems. It looks like the behavior of your 485 is different in different settings. As the first issue are you debugging the intensity? Do you have too bright, or too dim brightness, does intensity control make any difference? HV supply voltage of 2000V is low. What is the impedance of your 1000x probe? Looking at the schematic ¡°CATH REG¡± can only adjust ~ +/-100V so this is outside adjustment range. Should be the first thing to fix since everything else with intensity depends on it. Feedback loop around U1624 uses +50V at the top of R1642B as the reference. Is +50V correct? If you look at pins 2 and 3 of U1624 what voltage do you measure (should be essentially the same and close to 0V). Once you fix the HV supply if intensity is still problematic: There are multiple posts about DC restorer issues I recommend you search "DC restorer" "Grid Bias" for useful information. The ones I know well are: Topic #180156: Although different equipment, this topic has some DC restorer debug. Topic #180235??is a 485 with intensity control issues. In particular looking at the circuitry around intensity control pots. If you review both chains from start there is some relevant information. For time base issues, in the problematic 3 fastest settings how does the "A Sweep" and "A gate" signals look? They are easily available at the back of the scope with a BNC connection. Ozan |
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Re: Tek 2225 that wont power up after a knock :-(
Hi Ozan,
Try to find in the Files section a document called (I believe) "Repair tips for 22XX power supplies" I'm not at home now, so I can not look for a direct link right now, but the document made by Hakan, also a member here, described how to eliminate and look for which part of the ps is failing. Usually it is the first switcher, but the document describes how to test for that. Let me know if you found the doc. Leo |
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Re: Interesting Tek Documentary
Hi:
I've seen parts of it (or maybe the whole thing) before on YouTube. The Museum has some films... and from time to time some other YouTube channels post these old films. I'm not sure what OPB has to do with it? (Apparently they used old footage, and new narration, to produce a "new" show.) They are selling a DVD of it. Did they get the rights from Tektronix?... from the Museum? -- Roy Thistle |
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Re: Tek 2225 that wont power up after a knock :-(
Shorted Q913 could cause what you saw. However, did you measure it in place or after disconnecting from the circuit? Someone suggested I check C914 - I know its 15uF but do you know theAll component information is in the service manual. Section 8-9 (Page 113 in the PDF I am looking at) shows 15uF, 20%, 63V. I don't see why it would cause this issue after a knock but now all the components (including caps) did exceed their expected voltage by a large margin so they could be damaged. For example C971 is rated 50V but was stressed to 63V. Some components will survive brief over voltage, some may be damaged. In particular ICs may go into "latch up" and draw excessive current. Ozan Ozan |
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Re: Tek 2225 that wont power up after a knock :-(
I have identified that Q913 is short circuit between E,B&C and I also suspect Q923, but until I get them out that's as far as I've got.
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I cannot see any bulging caps or burnt components, damaged traces or other obvious issues and I've looked very closely. Someone suggested I check C914 - I know its 15uF but do you know the rating ?? Thanks for the tips. I'm just concerned for the cause - it wasn't powered when knocked. Perhaps it's just coincidence and it was a fault just in waiting ;-) Dave On 16/03/2021 17:51, Ozan wrote:
Hi Dave, |
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
Why did the open filter capacitor destroy the 741s? Surely open filter capacitors is a problem the tester should identify and not itself fail from.
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Larry On 3/16/2021 12:01 PM, ebrucehunter via groups.io wrote:
I resolved the problem. My confusion was cased by the Tek 070-1304-00 August 1974 manual for the TM501 found on TEKWIKI. This earlier manual shows Q10 on the left and Q12 on the right. The later 070-1304-01 June 1985 revision found on BAMA agrees with the configuration of my unit. Either the earlier TM501 units were configured differently or the original Tek documentation was in error. --
Best wishes, Larry McDavid W6FUB Anaheim, California (SE of Los Angeles, near Disneyland) |
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Re: I built a TM500 mainframe tester, and updated the design. Someone might find this useful?
I resolved the problem. My confusion was cased by the Tek 070-1304-00 August 1974 manual for the TM501 found on TEKWIKI. This earlier manual shows Q10 on the left and Q12 on the right. The later 070-1304-01 June 1985 revision found on BAMA agrees with the configuration of my unit. Either the earlier TM501 units were configured differently or the original Tek documentation was in error.
It turned out the 2000 uFd filter capacitor for the +33.5V supply was completely open, causing the TM501 to output a half-wave rectified waveform. This destroyed the 741 op amps in both 15V supplies. I installed sockets for the replacements. This exercise impressed me with the importance of testing these aged frames before plugging-in valuable modules. Fortunately, I did not try and use this one until now. My thanks again to Jared Cabot for this useful tool. Bruce, KG6OJI |
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