Re: Help no longer required finding a Tek 466 power rail short
Morning all.
Think I can resolve this one.
The +15v bridge was over-heating due to U1846, The -8v bridge is overheating due to something on the A5 board. The +5v bridge I'm not yet sure, however there are still the odd situation, such as Q1284 and Q1286 are very hot.
Anyway, I think I should end this thread now, as the original 'power rail short' has been resolved. Not only can I now see the wood, I can now see some of the incricate carved detail upon that wood!
The entire situation arose because the +5v and -8v bridges were running hot and it was decided to upgrade them. And now the same problem remains (although the -8v should be straightforward). If I get stuck, I'll start a new thread.
I cannot thank everyone enough for all the time, support and guidance. There are gems of info in this thread.
Game-changers for me, were printing out the components diagram from the manual and separately colouring in each power rail and also printing out an enlarged +65v section.
I have learned that I need a finer voltmeter.
Maybe even 2 scopes :)
I gained my first experience with a dimbulb tester
I have learned to pay more attention when re-assembling
And not to turn on the scope after disconnecting components
James
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Re: Wanted, Small flexible shaft coupling.
There is a product called "PIG PUTTY" that i believe is the same thing as plumbers epoxy. I have used it for repairs that involved a good deal of strength.
A skilled trade tool and die guy repaired a 30,000 PSI extrusion die with this stuff. It worked for more than a year till it was replaced.
It is machinable, so you can grind it after it has set, use something like a Dremel,or hand files, if you need to do any touch up.
Just prepare the surface with a little sanding and cleaning with solvent. Like alcohol or acetone.
Push it into the crack with a toothpick. Leave some excess on the outer surface.
Wally KC9INK
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Re: Wanted, Small flexible shaft coupling.
I agree with those suggesting somehow making a metal band to go round the OD of the cracked Al coupling. All you really need is something that can take the hoop force and allow the setscrew to do its job (and be accessible for tightening). Another, more complicated option is to pin it together, say, by drilling a tiny hole through the coupling and shaft, and inserting a pin or wire through to take the torque. A dab of epoxy would hold it nicely in place if there's too much lash from imperfect fitting.
I also like the flexible tube coupling methods - I've used this kind of deal on small motor/gearbox drive connections. A plus is that you can get a slip clutch torque limit action, but a minus is that it's hard to get axial force control - you can inadvertently pull the knob and shaft out of the coupling - unless there are other features to limit the travel.
All in all, this is a fairly simple, non-critical, and low speed and torque application, so lots of choices are available. Even a carefully placed, big gob of epoxy over the re-assembled, cracked coupling joint and pot shaft end would probably be good enough, practically speaking. As long as the flexible part of the coupling is intact, it should work pretty well, and you won't see the ugly stuff behind the front panel anyway.
Ed
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Re: Help required finding a Tek 466 power rail short
Perhaps spoke too soon but we are close.
The +15v bridge rectifier is running at scorching hot and the -8 and +5v are not far behind.
this was the initial finding when I had first fixed the scope way back when...
The trace disappears after maybe fifteen minutes and only half appears with the beam-finder there-after.
I'm off to bed, and shall have another look in the morning, but we definitely still have a detail to resolve.
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Re: Help required finding a Tek 466 power rail short
WOOHOO!!!!
Oh my gosh!
IT LIVES!!!!!!
I was in such a hurry earlier that didn't even touch any controls, however turning the storage off, resolves the problem.
Now I need to properly reassemble the A5 board set-up, and all the front panel and controls.
Not sure if this is because it is all half dismantled still, but the 'vertical position' control doesn't raise the wave above the median line
I know it is not yet 100% resolved, but I still lack the words to convey my gratitude.
What a mission! What a challenge!
Have learned invaluable information along the way. Tomorrow, I shall find the correct components, and hopefully the vertical postioning will be resolved.
It is difficult to know who to thank the most....
James
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Found the problem(s). Had tested the tubes some years back on an old emissions tester I have, and they looked "good". Picked up a Philco 7052 Mutual Conductance tester about three years ago, and finally got around to replacing one paper capacitor, and one electrolytic, and checking/calibrating it. The 7052 is just a re-packaged Hickok 533A, so tube data and components/wiring are the same.
Went back to the 130 this evening and checked all the tubes on the 7052 (except the rectifier and VR tubes as the voltages look fine). Lo and behold there were one 6U8 out of spec. (weak, one of the buffers), and V70 was severely out. Since V70 is the multivibrator, I suspect that was the major issue. V110, a 6BH6 is the Guard Voltage tube, and it also proved to be weak. I was fortunate enough to have a sleeve of NOS 6U8A tubes in stock, plus a very strong 6BH6 used tube. Replaced these tubes and the meter will zero with ease and no longer has the wild swings. After about 30 minutes warm-up, it stabilizes quite well.
With a little luck, I will try to calibrate it Wednesday or Thursday.
Thank you all for the guidance.
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On 3/22/22 08:55, Albert Otten wrote: Jerome,
The procedure for adjusting the variable osc. is:
"Set the COARSE ZERO control about 10 degrees above right horizontal,
and the FINE ZERO control at full capacitance, index horizontal to the
right. Set the internal screwdriver control, C2 (see Figure 5-3), at
mid-range, slot vertical. C2 is mounted on the FINE ZERO capacitor. Set
the variable oscillator also to 140 kc by adjusting the tuning slug in
T1 (Figure 5-3). The variable-oscillator signal appears at the GUARD
VOLTAGE terminal."
All that said, I have found several inconsistencies between Tek manuals
for the same device, but of later printing before. The Factory Calibration calls for 20 degrees. But remember that this is merely a preliminary setting before further tuning of T1 is done with the S-30. If the latter works (meter can be zeroed in the iterative process) then the initial setting (degrees) was simply OK.
As for the "bounce", it is definitely not normal, as at times it can
become quite savage, pegging the needle at either end of the scale. If you perform the the procedure in message 126515 to tune T1 then you don't need the display meter at all. After that you can pay attention to the meter problem.
Albert
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Re: Help required finding a Tek 466 power rail short
James,
If you are in storage mode, David T. is right. If not, see if your d-c restorer diodes, CR1444 and CR1445, are bad along with R1445. The diodes can be replaced with 1N4937 and the resistor replaced with a Vishay VR37 series. I think by your description, David T. called it right.
Mark
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Re: Wanted, Small flexible shaft coupling.
I had the very same problem and I solved it using a drop of epoxy and wrapping the broken ALUMINUM piece (not the plastic one) with copper wire and twisted the ends as Jeff said. It was meant to be temporary but it is still there several years later.
Regards,
Ignacio EB4APL
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El 28/03/2022 a las 0:58, Jeff Dutky escribi¨®: Jim,
The metal shells on these flexible couplings seem to be made of aluminum, and are quite small (maybe 1 cm in diameter). Is it really possible to TIG weld so small an item?
I had been looking online for information about soldering aluminum. There are videos showing this being done with special flux and solder, specifically to repair radiator coils, but I was going to try it with two flexible couplings from my 485 that have suffered similar failures. I think that I can heat the parts to the required temperature using my hot air rework station. I just need to get some of the special flux and solder.
The failures appear to be caused by the sharp corner designed into the shell where it engages with the plastic insert. The two failures I have observed on the 485 were on the vertical position controls, whose pots were not at all difficult to turn. I suspect that the sharp corner combined with 50 years of normal mechanical stress resulted in the cracks we see, not over-tightening of the set screws (but I don't know this: the 485 was apparently worked on by someone who did not have the best grasp of what they were doing, or didn't care to do a good job). In any case, the sharp corners clearly nucleate the cracks.
A temporary solution that I have considered, but have not attempted, is to simply wrap the plastic inserts in bus wire and twiste the ends together to achieve the required inward pressure.
-- Jeff Dutky
--
El software de antivirus Avast ha analizado este correo electr¨®nico en busca de virus.
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Re: Wanted, Small flexible shaft coupling.
I repaired a similar flexible coupling by finding some thin-walled aluminum pipe that happened to fit tightly over it. I cut it to length, drilled a hole where the set screw went, and slipped it over the broken part with a little epoxy to hold it in place. Not sure if the outside diameter of this one would happen to be the right size for a given tube but it might be an option.
Thanks,
Barry - N4BUQ
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----- Original Message ----- From: "Jared Cabot via groups.io" <jaredcabot@...>
To: "tekscopes" <[email protected]>
Sent: Sunday, March 27, 2022 6:22:27 PM
Subject: Re: [TekScopes] Wanted, Small flexible shaft coupling. Yeah, this unit was definitely the subject of a few ham-fisted repairs in the
past, including some incorrect re-routing of PCB traces, so I don't doubt the
part I am looking for was set up for failure at that time.
I don't have the means to TIG weld the part (DIY of this type isn't so common
here in Japan, just finding someone to do it to start with isn't easy..) if I
were still back in Australia, I'd have a workshop full of welders to choose
from.
I don't have machining capabilities yet until I get around to building a
workshop, so I was thinking of maybe getting some aluminium pipe or rod and
attacking it with a file and battery drill.
I do have a possible lead on a replacement part though so I'll see how that pans
out first.
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Re: Wanted, Small flexible shaft coupling.
If I imagine it properly, that same kind of coupling is in the 7A26 and 7A18 plugins.? It's? similar to a coupling needed for driving a leadscrew from a stepper for a 3D printer.
1) you could try to fake the aluminum pieces by 3D printing them, then take a piece of sheet rubber and make the gasket.? You may not need that.
2) you could look for a flexible coupler for a 3D printer, perhaps for 3mm shafts, and see if that works.? May or may not insulate which you may or may not need.
Akihabara? could be your friend.
Harvey
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On 3/27/2022 7:22 PM, Jared Cabot via groups.io wrote: Yeah, this unit was definitely the subject of a few ham-fisted repairs in the past, including some incorrect re-routing of PCB traces, so I don't doubt the part I am looking for was set up for failure at that time.
I don't have the means to TIG weld the part (DIY of this type isn't so common here in Japan, just finding someone to do it to start with isn't easy..) if I were still back in Australia, I'd have a workshop full of welders to choose from.
I don't have machining capabilities yet until I get around to building a workshop, so I was thinking of maybe getting some aluminium pipe or rod and attacking it with a file and battery drill.
I do have a possible lead on a replacement part though so I'll see how that pans out first.
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Re: Wanted, Small flexible shaft coupling.
Yeah, this unit was definitely the subject of a few ham-fisted repairs in the past, including some incorrect re-routing of PCB traces, so I don't doubt the part I am looking for was set up for failure at that time.
I don't have the means to TIG weld the part (DIY of this type isn't so common here in Japan, just finding someone to do it to start with isn't easy..) if I were still back in Australia, I'd have a workshop full of welders to choose from.
I don't have machining capabilities yet until I get around to building a workshop, so I was thinking of maybe getting some aluminium pipe or rod and attacking it with a file and battery drill.
I do have a possible lead on a replacement part though so I'll see how that pans out first.
|
Re: Wanted, Small flexible shaft coupling.
Jim,
The metal shells on these flexible couplings seem to be made of aluminum, and are quite small (maybe 1 cm in diameter). Is it really possible to TIG weld so small an item?
I had been looking online for information about soldering aluminum. There are videos showing this being done with special flux and solder, specifically to repair radiator coils, but I was going to try it with two flexible couplings from my 485 that have suffered similar failures. I think that I can heat the parts to the required temperature using my hot air rework station. I just need to get some of the special flux and solder.
The failures appear to be caused by the sharp corner designed into the shell where it engages with the plastic insert. The two failures I have observed on the 485 were on the vertical position controls, whose pots were not at all difficult to turn. I suspect that the sharp corner combined with 50 years of normal mechanical stress resulted in the cracks we see, not over-tightening of the set screws (but I don't know this: the 485 was apparently worked on by someone who did not have the best grasp of what they were doing, or didn't care to do a good job). In any case, the sharp corners clearly nucleate the cracks.
A temporary solution that I have considered, but have not attempted, is to simply wrap the plastic inserts in bus wire and twiste the ends together to achieve the required inward pressure.
-- Jeff Dutky
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Re: Revisited: Help required finding a Tek 466 power rail short
On Mon, Mar 28, 2022 at 12:20 AM, Raymond Domp Frank wrote:
I was wondering whether one other component isn't necessarily broken: R948.
Still talking to myself: Hm, not if pot has been unmoved from position "B ends A", i.e. S948 closed and R948's wiper at the "anode CR949 end" and internal resistance in R948 small enough in that position. Raymond
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Re: Revisited: Help required finding a Tek 466 power rail short
On Mon, Mar 28, 2022 at 12:20 AM, Raymond Domp Frank wrote:
With R948's wiper approaching or reaching CR949's anode, power dissipation
would kill it.
To be more clear: "it" being R948. Raymond
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Re: Wanted, Small flexible shaft coupling.
On Sun, Mar 27, 2022 at 01:43 AM, Jared Cabot wrote: Hi all, I have a DC503 that I have rebuilt except for a shaft coupling that
has broken as they often seem to do.
Does anyone have one of these they are able to sell and send to me here in
Japan?
It looks to me like it might be possible to repair the piece you have. If it's steel, solder or braze it; if it's alum, find someone to TIG weld it. It's likely that it broke because someone overtightened it, which may have seemed necessary because whatever it is driving required too much torque. See if you can lubricate that before you do anything else.
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Revisited: Help required finding a Tek 466 power rail short
Now that the power rail short has been explained (a short between +5V and +65V), I was wondering whether one other component isn't necessarily broken: R948.
We've been told that CR948, CR949 and VR948 have broken down. So, what may have happened? I guess CR948 shorted or started leaking heavily, causing CR949 and VR948 to be connected straight to +65V, when S948 is closed and R948 "against" CR949's anode. This in turn would cause the +65V supply to be overloaded (while supplying current into the +5V), causing it to fall to a about +5V. Since the +65V supply is the reference for the 466's LVPS, all PS voltages broke down. With R948's wiper approaching or reaching CR949's anode, power dissipation would kill it. I haven't thought through if S948 is supposed to close near or in that position. If at the other side (+65V), S948 may have become stuck closed.
A breakdown only in CR949 and/or VR948 but not in CR948 would not cause the power rail (almost) short, whatever the position of the R948 wiper, unless it had a short between both ends, as Mark suspected.
So, as far as I can see, either there's a short between R948's end points, which seems unlikely to be caused by a malfunction in R948 itself, or R948 has been destroyed by the above events. If the former, replacing the defective CR948, CR949 and VR948 would immediately destroy the new CR949 and VR948 but not CR948. If the latter, the 'scope would work ok, just with unadjustable A trigger holdoff.
Any thoughts?
Raymond
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Re: Help required finding a Tek 466 power rail short
Quick check reveals all the LV supplies are still in order
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Re: Help required finding a Tek 466 power rail short
Very quickly as have to go out for the evening.
Changed the components, turned the scope on and appeared a nice clean trace.
After 10 seconds or so the trace faded and the CRT started to fill with intense bright green light.
After reducing the 'intensity' to min, it remained with two separate blurry areas, like unfocused spots on the screen.
No time now to test anything but shall welcome any opinions.
Thanks
James
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Re: Help required finding a Tek 466 power rail short
On Sun, Mar 27, 2022 at 12:59 PM, James55 wrote: 1N4148's are not a problem, but for the 3v Zener, only have the choice
between a 3.3v and a 2.5v until the shops open tomorrow.
3.3V would be fine. Ozan
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Re: Help required finding a Tek 466 power rail short
On Sun, Mar 27, 2022 at 05:19 PM, Mark Vincent wrote:
James,
A 1N4148 will work to replace the 1N4610.
Mark
1N4148's are not a problem, but for the 3v Zener, only have the choice between a 3.3v and a 2.5v until the shops open tomorrow. Would be great just to do a test, just in case I have missed something?
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James55
Jared Cabot
Raymond Domp Frank