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Re: A bewitched voltage divider?
Is it still connected to the 4051 during measurements? Try without any other connections and of course be aware of the DVM load effects. If the 4051 is leaky, it could cause grief. Also try getting a reading from the output of the mux while the divider output is shorted to ground.
Ed |
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Help! 2465A CRT Focus Troubles
Hello
I am at a standstill with figuring out why the CRT of my 2465A is blurry and won't focus. I purchased this unit from Government Planet last summer with the idea that I would probably have to troubleshoot it. I turned it on and it made a screeching sound and had no display. I thought the sound was coming from the fan but no it was the high voltage board. Checked the voltages on J119 and they were all good with the exception of the -15V rail which had high ripple. Decided to recap the LVPS with a kit from Condor Audio. This fixed the -15V rail. Turned it on and there was a blurry dispay but intermittent screeching from the high voltage board. Looked closer at this and discovered that the ceramic of T1970 was cracked in several places. Purchased a new high voltage board from QService and installed it. Now no screeching but the display remains blurry with the Read Out letters wider and taller than they should be and the same for the traces. I have uploaded 2 pictures to the file Amberwave 2465a that shows what I'm talking about. I checked voltages to the CRT socket at pins 8(31V), 12(-108V to -186V) and 13(-192V to -224V) and they look reasonable. DAC reference is right at 10V. When I input a signal into the scope I can just make out that it is a sign wave. I just don't know where to go from here. I have invested a lot of time and dollars in this scope to just give up. It would seem that this isn't a HV board issue as both boards gave a blurry image. Could this be the CRT tube itself or one of the IC's? I would really appreciate some guidance on where to go from here from someone more experienced with these scopes than me Rusty Hilliard W0RGH |
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Re: A bewitched voltage divider?
Gianni,
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According to the schematic, cathode voltage is supposed to be -1600 V. At 1000:1 divider would give 1.60 V, which it does. You say the input is -1510 V. Have you verified the accuracy of the HV probe and "VOM (or whatever meter type in use)?" The resistors there may have drifted. --Robert On 2/20/2025 2:49 AM, Gianni Becattini via groups.io wrote:
Hi Guys, |
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Re: A bewitched voltage divider?
On Thu, Feb 20, 2025 at 4:49?AM Gianni Becattini via groups.io
<Giovanni.becattini@...> wrote: I will be very grateful for any help, I am getting crazy. Thanks GianniThis is how I felt until I discovered that my 485 had a voltage dependent "precision" resistor in the circuit that derives 13V from the 50V rail. See /g/TekScopes/message/113493. I have no idea why this happened, nor how common it is, but apparently it can happen. In your case I guess it could be as simple as some kind of contamination on or around the 10M resistors, which doesn't affect your DMM measurements, but appears at the working voltage? |
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A bewitched voltage divider?
Hi Guys,
I am trying to fix some problems on my 11302, but I am stuck on a problem that seems very simple, but which I cannot overcome: a simple voltage divider. I am probably doing something wrong, but I cannot guess what (I added an album among the photos with the simplified schematic diagram). The 11302 "reads" the CRT cathode voltage using a voltage divider, selected by a 4051 analog multiplexer. It should be simple: the voltage divider is made up of a 20 M ohm and a 20 kohm resistor (the former is actually 2 x 10 Mohm resistors). So the output should be one volt for every 1000 volts in the input (well, 0.999). For me this is not the case: the divider output is significantly higher than it should be (with -1.6 V in the output, the input is actually -1.510 V). Easy, you say, one of the resistors has changed its value over time, but it is not so. I desoldered one extreme of them and they are all very precise. Another hypothesis was that the CRT mesh was causing some problem, but it is not: I disconnected it and nothing changed. I neglected the C1100 and C1420 capacitors because they could only lower the voltage, not make it greater. The last thing I didn't check yet is the dirt on the lower part of the board, but before disassembling it I wanted to hear your suggestions, if you like. I will be very grateful for any help, I am getting crazy. Thanks Gianni |
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Added photo album Bewitched voltage divider (11302)
#photo-notice
Group Notification
Gianni Becattini <Giovanni.becattini@...> added the photo album Bewitched voltage divider (11302) ( /g/TekScopes/album?id=300803 ) : see my emailò
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Re: Tektronix 145 PAL test signal generator - repair (oven control circuit and maybe more)
Hi all
Thanks for your inputs... yes it's mostly for preservation reasons... how many people or institutions are left with a functional Tektronix 145? I initially picked it up for spares but it's so well made it would be sad to trash it if repair is possible. If I can't get the crystal oven to work or other BER situation I can still gut it. I do have old PAL televisions to repair/restore so it could also theoretically serve a purpose. I'm not sure replacing the resistor will help with anything.. it reads within spec, is °C 130~ too hot for a larger resistor? I checked all the socketed transistors and they're OK. The thermistor is not open, though I'm not sure about its value (I should probably remove it out of circuit to check). I will have a look into the power supply section and try to get it within spec before I continue. After 30 mins of waiting, the TP1100 voltage stopped at 3.95 V (the manual says it should come on before 20 mins - the recommended warmup time). Maybe it does need the PSU section dialed in. |
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Re: Extender Card for TM500/TM5000 with Test points on every line.
I have my boards made at PCBWay. They produce extremely high quality boards at very reasonable prices. When gold fingers are involved using the traditional gold over nickel the fingers are electroplated which takes extensive time and Gold is EXPENSIVE. The difference in cost between the 5 board minimum and 25 boards is only about $35, once you cover the extra setup. If I pursue the project, they will also do a 30 degree bevel on the finger end of the board to allow it to fit into the female connector easily. I am investigating a less costly but still rugged finger treatment called Enepig (electroless nickel electroless palladium immersion gold). This finish is cheaper to apply than the the electroplated gold over nickel, but still make a set of boards in the $150 + range instead of the $20+ range.
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Another expensive item is the Female connector. I plan to use the Sullins ECM28DRKN-S!3 which can be ordered from Digikey for $10.72 each, but minimum order is 10 pcs. This very high quality connector uses full bellows Gold over Nickel phosphor bronze contacts. The contacts and the plastic are rated at 125 degrees C. The gold plated 4-pin headers are not cheap, either and 56 of them are required for each extender board. FCI part number 95293--101-04LH (30u" gold over NI) or 95283-801LF (15u" Gold over NI). The Jumpers are also expensive: FCI 65474-001. 56 required, 60 recommended in case you lose a couple. The design is very high quality, but as a result it is not cheap. Actually the construction will be superior to the male end of my Tek 067-0645-02 TM500 extender cable. The male end of their cable did not have the 30 degree bevel which makes it much harder to insert into a female connector than the typical plug in. I am continuing to research the costs for this project, but it is not going to come in at the $50 price of the one on eBay that uses raw copper for the board and fingers, with no test points. Hopefully there will be enough interest to group buy the parts. Steve On 2025-02-18 10:22, Roy Thistle via groups.io wrote:
On Mon, Feb 17, 2025 at 12:56 PM, Eric Garner wrote:Not to dissuade OP from their projectWell... many of us...on this forum... IMO... are hobbyists. |
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Re: Tektronix 145 PAL test signal generator - repair (oven control circuit and maybe more)
Luca,
R1156 is too hot. Replace with a 5W. Look around the TP1100 for bad parts. The thermistor could be open. Dirty pins/sockets could be the problem. Check the ripple in the power supply. At the age of this unit, recapping may be necessary. Mark |
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Re: Tektronix 145 PAL test signal generator - repair (oven control circuit and maybe more)
To fix PAL standard televisions?
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Yes, people are into preserving antique televisions and equipment. Now if 145 PAL does not refer to test equipment for the non-NTSC standard televisions them I am out. Frank DuVal On 2/19/2025 11:44 AM, EB4APL via groups.io wrote:
Excuse me, but why you would want a functional PAL signal generator? |
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Re: Tektronix 145 PAL test signal generator - repair (oven control circuit and maybe more)
Excuse me, but why you would want a functional PAL signal generator?
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El 19/02/2025 a las 17:31, Luca via groups.io escribió:
Hi all --
Este correo electrónico ha sido analizado en busca de virus por el software antivirus de Avast. www.avast.com |
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Tektronix 145 PAL test signal generator - repair (oven control circuit and maybe more)
Hi all
Here /g/TekScopes/topic/107425848 H?kan kindly provided the service manual for this signal generator. I had time to have a look inside and found a shorted cap on the -15V supply (C1200 of A13 board), now the power supply seems to behave a bit better (the 3.6 V rail is still off, at 3.3~ ish Volts) According to the manual the oven temp normal light should come on but this never happens (this circuit doesn't seem to use the 3.6V rail so I ignored it for now) The manual says that TP1100 should be around 4.1-4.2 Volts for the "oven temp normal" light to come on but that never happens.. it hovers around 3.5 V and varies a bit. I noticed that R1156 gets really hot (>100 °C) but I don't know if this is a fault or not. I took the oven apart to check the thermal fuse but it seems ok... so I'm not really sure where to go from here. I updated the album: /g/TekScopes/album?id=296482 Can I plug the oven in without enclosure for testing? Disclaimer: I obviously have no idea what I'm doing... there doesn't appear to be any notable occurences of this SG on the net so I will try to find faulty or out of spec parts and hope any of you have a good idea where to start Thanks Luca |
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Re: electronics help?
Hi All,
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The items are mainly TM500 / 5000 series plug ins and 7000 series scopes and plug ins... Most of which I believe were purchased from the Tek Country store over the last 2-3 decades. She already has a buyer; I'd suspect you will see some of this stuff at the local PNW Ham Radio / Electronics swapmeets soon.??Nothing that is usable will go in the trash.?? Thanks,?Ryan On Friday, February 14, 2025 at 08:23:11 AM PST, icy.dev via groups.io <icy.dev@...> wrote:
Ryan, Please post a list of what she has available!!! Esp if close to Portland. My daughter is there and can pick up for me!!?? |
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Re: KO4BB Manuals not working?
Funny, When I google ko4bb and click on Manuals, I can get to any manual that is a file listed on that page. But if I click on a folder, then it goes to Home page.
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Frank DuVal On 2/18/2025 5:46 AM, Tom Gardner via groups.io wrote:
On Tue, 18 Feb 2025 at 06:23, Sam Reaves via groups.io <sam.reaves= |
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Re: Extender Card for TM500/TM5000 with Test points on every line.
On Mon, Feb 17, 2025 at 12:56 PM, Eric Garner wrote:
Well... many of us...on this forum... IMO... are hobbyists. Probably, I am not very smart... but AFAICT... time, connectors, and fiddling around with shipping, can be expensive... but, high quality PCB are not. On way around the distribution problem is to register a 'project' with a PCB manufacturer, and then anyone can order the PCB. Also, at least down to common components, the PCB manufacturer can also manufacture the thing to that level, and even provide a kit. The connectors for these...ARAIK... are not as much of a problem sourcing anymore. If one is worried about quality, and not their wallet... then buying the Tektronix ones... when they show up... might be a better solution. -- Roy Thistle |
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Re: Extender Card for TM500/TM5000 with Test points on every line.
On Fri, Feb 14, 2025 at 07:49 PM, <info@...> wrote:
Hi: AFAIK... there have been a few projects about/similar to this. If you have the time, and the desire... can you explain why they cost 150.00 each? -- Roy Thistle |
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Re: KO4BB Manuals not working?
On Tue, 18 Feb 2025 at 06:23, Sam Reaves via groups.io <sam.reaves=
[email protected]> wrote: Does anyone know what is going on with ko4bb,com? The owner has been having capacity problems. Due to that I would only make sparing use of a workaround: |
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