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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

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

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?

On Sun, Mar 27, 2022 at 09:38 PM, Raymond Domp Frank wrote:

without that shorted, +5V and +65V wouldn't be shorted together and CR948
and
CR949 wouldn't have blown.

... and neither would VR948.

Correction: Unless CR948 shorted out and then, depending on position of S948 and R948...

Raymond

I think the design lab at a place I worked '94-'96 had one of these. Off line power supply OEM. They used fiber optics I think.

Current employer we've done a lot of work on hybrid electric drives for off-road equipment. 700VDC -> 480v 3ph motor drives, some over 100kW.

All the lab work on that stuff we've used differential to single ended probes made by Tek, Lecroy, and one other brand I forget. Most are Tek ones though. I've looked at a lot of IGBT gate drive waveforms on the inverters with those probes.

On Sun, Mar 27, 2022 at 09:35 PM, Raymond Domp Frank wrote:

without that shorted, +5V and +65V wouldn't be shorted together and CR948 and
CR949 wouldn't have blown.

... and neither would VR948.

Raymond

On Sun, Mar 27, 2022 at 08:49 PM, James55 wrote:

You were spot on, and thankfully I had managed to locate exactly what you had
suggested. In fact, the VR 948 zener is also bad.

It would have to, to make sense of your findings. Don't forget to check R948 (trigger holdoff pot) for a short across, as Mark suggests; without that shorted, +5V and +65V wouldn't be shorted together and CR948 and CR949 wouldn't have blown.

Raymond

Yup, beam finder is what I meant. I cleaned the pots inside and it loosened up enough to turn the knob.

This was really helpful! I took the lid off and used cleaner on the pots and it loosened up!

Mark

I have just seen your post.

You were spot on, and thankfully I had managed to locate exactly what you had suggested. In fact, the VR 948 zener is also bad.

Thank you


James

Can you machine out a brass ring that fits on the outside of it? You might even be able to find a flat washer that has a large inside diameter to fit the outside diameter of the coupling. Double up a few of them for strength. If that is an option, apply some epoxy in the crack before you slip the brass ring (or the washers) over.

I have had some luck with flexible tubing, either on the shaft itself, or
over the top of the broken coupling - it only works if the angle is not too
extreme, but I have been able to make that work in a few cases.

On Sun, Mar 27, 2022 at 1:43 AM Jared Cabot via groups.io <jaredcabot=
[email protected]> 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?




Thanks!
Jared

--
Andy

And with the A5 reconnected to the scope, all the LV rails are once again fine.

So, I have obviosly learnt something during this long thread...

Hat off to you all.

Now just need to find suitable diodes.


James

James,

A 1N4148 will work to replace the 1N4610.

Mark

So, after re-checking all the caps for shorts, and then removing the chips to no avail, I moved on to testing every diode and may have found the problem.

CR948 (Tek 152-0333-00) and CR949 (1N4152) were (and still are) shorted out.

With these two lifted from the circuit we no longer have the low 4Ω reading between the +65 and +5v rails, so fingers crossed it is only these two.

For sure I don't have a 152-0333-00 (1N4610) here, although I do have various diodes here, if anyone has a suggestion as to a temporary replacement, in order to test the scope?


James

Rick,

From my experience, I oil each shaft and set screw outside and inside. Age and electrolysis will cause parts to be stiff or seize. A drop of oil on a small screwdriver end is used to put on in areas where the oil can tip cannot reach. After enough time, there is little to no lubrication left making metal shafts stiff. I have even heated shafts with a soldering iron using the tip near where it is close to the heating element resting on the shaft long enough (a minute or more depending upon the shaft diameter and amount of heat desired to get it loose again) to get it hot enough to make the hard oil a liquid again or it will burn off then add new oil. That has worked to make a shaft that is very stiff to locked to easy to turn again. Shafts and collars that are Al can lock solid due to oxidation and must be replaced.

Mark

James,

On page <7>, there is part of the A5 board in the centre where the 5 and 65V are tied through parts. Check the 948 and 949 parts. Maybe the A Trig. Holdoff pot is shorted from each end, diodes shorted or something wired wrong. I could be wrong about any of these being bad. I would check here first to see if something is bad/wrong then if all are good, move on to other areas. If someone else knows otherwise, jump in. This was my guess where to start.

Mark

Jean-Paul wrote on 3/27/2022 10:14 AM:

Jared send the spec, dimensions photos ?

Perhaps DIY if you have access to lathe, or machine shup.

Perhaps a local Japanese mechanical parts house?

Hello--

Would a short length of flexible tubing (e.g., automobile-engine? gas
line) and a couple of worm-drive clamps serve as a replacement until the real thing shows up?

73--
Brad? AA1IP

Hi all,

Thanks for the suggestions.

Been a busy few days so haven't worked on the scope. Also didn't manage to get the prints I had wanted, but today is a free day, and this will be great practice in problem solving.

Just doing a quick resistance test across the LV rails (with the A5 board connected) reveals that between +65 and +5v there is only 4Ω, whereas with the A5 removed, the measurement is over 4.5kΩ, so for sure that needs to be looked into.
And in case anyone was wondering, the LV rails all return to their correct voltages with the A5 board removed again.



@ Roger,

If you want a quick check on which power rail is causing the problem you can completely and individually isolate +15V, +5V and -8V from the rest of the A5 board by lifting one side of the decoupling inductors L582, L584 and
L585, square 12C on the A5 component layout diagram (they are not shown on schematic <5> but are shown on the power distribution schematic). C582 and C584 are immediate suspects, but you may have already changed
them.

Unfortunately lifting none of the inductors resolved the short and yes the capacitors have recently been changed with 35v tantalums.



Wish me luck...


James

Hi all, I bought an old (I know, caveat emptor) 464 in order to learn how
to use a scope. I followed a simple tutorial that is supposed to show a
flat line sweeping across the screen but I can't get it to show up. If I
press the illum button, I can see the trace for a second. I can control its
vertical and rotation but again, only when I hit the illum button.

Also, the intensity know is REALLY stiff, maybe even stuck.

Any advice on how to start?

Thank you!

Rick