Tektronix 475A DM44 add-on.

[Biggles]

I have a Tektronix 475A scope with a DM44 multimeter unit piggy-backed on top which has been faulty since I acquired it. I have tried to undo the two screws which appear to hold the unit onto the top of the scope but there is something else attached preventing the unit from parting company. Does anyone have any tips on how to get this apart? Thanks.
Alan.

[frsimen]

Alan

I think you need to remove the outer case of the main scope too as the DM44 frame extends beyond the outer case opening.

Paula

[Biggles]

Thanks for the info Paula. I was hoping I wouldn't have to dismantle the whole lot. I will have to allocate a bit more time to investigate it fully. There are no readings at all on the DM44, although the display is lit up and reading 0. I thought there may be an input protection fuse blown or something simple but it looks like it may be a bit more complicated. Cheers.
Alan.

[ColinTheAmpMan1]

It's actually quite easy to take the case off any of the 400-series Tek scopes. Unscrew the screws holding the four feet/cord-wraps and remove them (if they are present - some scopes don't have them). There are also two more screws holding the back-panel on which should be removed, too. The back panel can them be taken off and the case carefully slid backward to remove it.

I say to remove the case carefully, as some wires/connectors, etc. may get disturbed otherwise, especially on DM44 options and the 468, all of which have the "penthouse" extension.

Something else needs attention, too. It is much easier to do all of this if the scope is sitting on its front panel, where all the knobs are located. If you have a front-cover, then using it will prevent damage to the knobs, switches, etc., otherwise, tread carefully.

I would also advocate getting the correct Service Manual for your scope. It can probably downloaded from several places (I would try Tekwiki first), but I prefer the genuine printed type. They are much easier to read because the scanned pdf versions are sometimes not at a good resolution, but also because the fold-out parts are so convenient. Tek manuals are generally not too expensive, say £15 well-spent.

Good Luck, Colin.

[Biggles]

Cheers Colin. I will probably wait until I have some spare time (a rare thing) and have a go at it. I use a separate DVM so it's not critical to fix it. It would just be nice to get it working. At the same time I don't want to cause further problems by removing the case incorrectly, as it's a very good scope.
Alan.

[evingar]

Originally Posted by ColinTheAmpMan1

I would also advocate getting the correct Service Manual for your scope. It can probably downloaded from several places (I would try Tekwiki first), but I prefer the genuine printed type. They are much easier to read because the scanned pdf versions are sometimes not at a good resolution, but also because the fold-out parts are so convenient. Tek manuals are generally not too expensive, say £15 well-spent.

I would agree with this.

If you want to go the download route (for free), the service manual can be downloaded directly from Tek

https://uk.tek.com/manual/475

[Biggles]

Thanks for the tip. I will try that before I start work on it. I have about five or six scopes of various pedigrees to repair on the "round tuit" pile but the 475A is a favourite. I rely on my Marconi 2955 RF test set a lot which has a basic scope on it too but it just extends to audio work. My main aim is to bring my spectrum analyser plug-in/scope back to life but it's just finding the time...
Alan.

[ColinTheAmpMan1]

Be aware that the 475 and 475A are different! The 475 manual may have some similarities, but you will really need the 475A manual. A pdf of the 475A instruction and Service manual for the 475A with DM44 is here:

http://bama.edebris.com/manuals/tek/...ndex-9595.html

Since my 468, which also has the "penthouse" extension on the case, is out of it's case, I just took a look at it. The "penthouse" is spot-welded onto the main part, so the whole thing has to come off...

Colin.

[Biggles]

Thanks Colin, I will take that on board. I have some outside work on at the moment to take advantage of the hot weather (antenna rigging) so it will probably be tackled on the next bout of rain/snow/wind we get.
Alan.