Re: 7623A: Let there be dot


 

Hi,

It may be that nothing you did caused a problem. Old capacitors sometimes do not last when operating voltages are restored. Pull the HV module and see what smoked and you may be able to see it run again. Experience is not lost.


Jerry Massengale



-----Original Message-----
From: empr1o
To: TekScopes
Sent: Fri, Apr 26, 2013 6:32 am
Subject: [TekScopes] Re: 7623A: Let there be dot

 

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" <rgwood@> 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
> > >
> > >
> > >
> > >
> >
>

Join TekScopes@groups.io to automatically receive all group messages.