Re: 7623A: Let there be dot


Don Black <donald_black@...>
 

Use all your senses. Look and smell and try to see where the smoke came from. It might not be as bad as you fear.

Don Black.

On 26-Apr-13 9:32 PM, empr1o wrote:
 


Oh Ed, I wish I could implement your recommendation, but I fear the worst.

Last night I was in a state of joy with beams tracing for all four channels. I tried to deal with the back shield and managed to blow a fuse and then when I replaced with another fuse I had on hand from another scope something went dreadfully wrong and a terrible smoke rose from the area around the HV I think---I'm not really sure what failed or where, so I can't say for sure.

The fact is, I think I blew it.

I have another scope that powered up with a blown CRT...back to the drawing board I guess. Hopefully my next patient doesn't die on the table...

--- In TekScopes@..., "Ed Breya" wrote:
>
> Once you figure out the gross failures, I'd recommend swapping the boards associated with the storage function so that those that went with the good CRT are kept. As I recall, there are a number of adjustments for storage mesh bias and flood gun settings, that are specific to the CRT. This may save some grief later, or maybe eliminate doing a lot of adjustments after it's working again.
>
> Ed
>
> --- In TekScopes@..., larrys@ wrote:
> >
> > You should have easily reachable power supply test points on the
> > vertical output board. They are helpful. Far as the shield issue
> > goes, make sure you aren't using 4-40 screws that are too long.
> > The shield goes over the LV regulator board. It often has solder
> > joint issues with the TO-3 series pass transistors. Stressing it
> > can make a supply (or more) go away. You will want a 7Axx in one
> > of the two left slots and a 7BXX in the right. Do you have the
> > manual?
> >
> > -ls-
> >
> >
> >
> >
> > "empr1o" wrote:
> > > Thanks guys. After I posted this I started to question my sanity and
> > > went to check if this was really what was happening. For the record,
> > > I realize that I took the shield off just because it was smashed
> > > up---probably what broke the crt to begin with.
> > >
> > > It really is something like making the last edge that puts the crt
> > > out---it isn't even just the dot, but the whole display--you know, the
> > > identify or <5V or whatever.
> > >
> > > It also can't be any kind of contact with the elements on the board.
> > > I've got bigger fish to fry, like figuring out if anything else is
> > > broken. I'm going to fix it in a spot that is safe and will work and
> > > make my way through the manual to see where I end up.
> > >
> > > Thanks all. This list is great.
> > >
> > >
> > >
> > > --- In TekScopes@..., "Rob" wrote:
> > > >
> > > > The following are best guesses from my experience with 7000 series
> > > scopes in general. I have not however worked on a 7623A..
> > > >
> > > >
> > > >
> > > > 7000 series in general do not sweep w/o plug-ins. Normally the
> > > “dot” is biased to not be visible so w/o plug-ins you don’t see
> > > anything (this can sometimes be overcome by getting the screen to
> > > flash somewhat with the beam finder w/o plug-ins).
> > > >
> > > >
> > > >
> > > > Anyway, I suspect changing the shielding is changing the bias and
> > > hence the dot appears and goes away when it is replaced.. I would
> > > replace the shielding and put a plug-in in and see what happens. If
> > > no-joy start troubleshooting with flow chart in the manual it is very
> > > good for other models.
> > > >
> > > >
> > > >
> > > > Anyway, my best guess. Hopefully helpful
> > > >
> > > > Rob
> > > >
> > > >
> > > >
> > > > From: TekScopes@... [mailto:TekScopes@...]
> > > On Behalf Of bonddaleena@
> > > > Sent: Thursday, April 25, 2013 7:38 PM
> > > > To: TekScopes@...
> > > > Subject: Re: [TekScopes] 7623A: Let there be dot
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > Good question. I have several 7623As. I have a mint one thatd did
> > > this:
> > > > I took the aluminum cover off the back because the fan was a little
> > > noisy. Measuring voltages on be board underneath, I heard a 'snap' and
> > > that was that. Never could get it going again. Have a bunch in various
> > > stages of 'repair', but I did get one going.
> > > > BTW, I bought a whole bunch of misc plug ins for this great old
> > > model, for almost nothing on ePay a while back... all good.
> > > >
> > > > ron
> > > > N4UE
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > >
> > > > -----Original Message-----
> > > > From: empr1o
> > > > To: TekScopes <TekScopes@...>
> > > > Sent: Thu, Apr 25, 2013 8:27 pm
> > > > Subject: [TekScopes] 7623A: Let there be dot
> > > >
> > > >
> > > >
> > > > Hi all.
> > > >
> > > > I preface this message with the disclaimer that I know nothing about
> > > scopes. One must start somewhere...
> > > >
> > > > I've come to own a 7623A that powered up but had a smashed crt. So,
> > > I track down another 7623A with a good tube that isn't powering up and
> > > move the good tube to the powering device.
> > > >
> > > > I power up the re-tubed scope and manage to find a dot. I can't
> > > remember if that happened with or without a plugin (I have a 7818,
> > > 7828 and a 7B53---no idea if those work at all either but that's
> > > another front...)
> > > >
> > > > The dot is a morale boost and I'm even more impressed with the
> > > craftsmanship and design of these things. Swapping crts was a cinch.
> > > >
> > > > My question is about the strange thing that happens next. I had to
> > > pull the board and fan on the back side to push the crt out, and after
> > > putting it all back together I didn't replace the perforated shield
> > > when I fired it out to see what gives.
> > > >
> > > > The next morning, I (reasonably I think) set off to close everything
> > > up properly so I can try to figure out how many of the other broken
> > > puzzle pieces I have can be snap together, and the power light doesn't
> > > come on. I shortly thereafter determine that the thing that is keeping
> > > the scope from returning to its signs-of-life status is the perforated
> > > shield on the back end that covers the board behind the fan. I put in
> > > a less bent cover and the light comes on but no dot. The only way I
> > > get the dot is when the shield is off completely.
> > > >
> > > > What is up with that? Is there something about how that metal shield
> > > fits in that is making a bad connection to the chassis? I tried a few
> > > 7623A shields (in various states of bent and straight-looking---yes, I
> > > have a stack of 7623as) and they all seem to make the same thing
> > > happen.
> > > >
> > > > Can someone tell me how to identify what is happening so I can try
> > > to make it right?
> > > >
> > >
> > >
> > >
> > >
> > > ------------------------------------
> > >
> > > Yahoo! Groups Links
> > >
> > >
> > >
> > >
> >
>


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