New (old) 2247a enquiry


Richard Merifield
 

Hi All

I could not help myself recently and purchased a Tek 2247a scope that is in superb condition. I have a modern Siglent but have never owned an analog scope.

I popped it open just to have a look. It is spotless, almost shining inside so I closed it back up. It seema to function properly on all channels. My question is whether it is worth replacing anything known to cause future problems? I will have a read of the manuals also.

Regards

Richard


 

Richard,

I have no direct experience fixing a 2247A, though I own a 2252, which is a slightly upgraded version of the 2247. The first principle for most Tek scopes is "if it ain't broke, don't fix it." If your scope is working, don't mess with things on the chance that they might fail later. Every time you put soldering iron to the PCB there is some damage that will occur, just from the heat exposure, so it's best not to do anything that is not actually necessary.

That said, there are a few things that are known to be ticking time bombs. The first is the RIFA safety cap. These tend to fail spectacularly, especially in 250 V mains systems (i.e. most of the rest of the world other than the USA). According to the service manual the 2247A appears to have three Y safety caps (C2213, C2214, and C2217, all PME271Y415 from RIFA) and two more (possibly X?) safety caps (C2215 and C2216, both F1772-415-2000 from Vishay). I would replace the RIFAs on sight, whether or not they are cracked and crazed. The Vishays I would leave alone.

Another thing to do, that doesn't not involve outright replacement of anything, is to open the scope up and give it a thorough visual inspection. Specifically look for leaking caps, in a scope of this age specifically leaking surface mount electrolytics. Look for damage to the PCB around such surface mount caps. You may need to use a magnifying glass or loupe. If you find any leaking caps or damage to the PCBs then you are justified in replacing them (maybe all of them, especially if they all look like they are the same part, even if only some of them have failed).

You would be well advised to take pictures of everything as you do the visual inspection, both so that you know how things were assembled, and so you can refer back to the images of the internals without having to open the scope up again.

-- Jeff Dutky


Richard Merifield
 

On Wed, Jun 23, 2021 at 08:21 PM, Jeff Dutky wrote:


well advised to ta
Thanks Jeff. I will pop it open again and inspect as you suggest. The RIFA safety caps seem like an obvious replacement.

I was originally put off once I saw all the ribbon cables etc that need to be removed to get to the power supply board. I will take my time and do some reading etc Its far more complex than the old solid state amplifiers I have been playing with :)

Regards

Richard


tekscopegroup@...
 

The highest priority preventive repair for any of the 224x scopes (2245, 2246/A, 2247A, and I am not also sure if the later model 2252 also requires it as well, is to replace all the rectifier diodes on the LV power supply board (total 17 diodes) that have either ZM or ZS marked on them as they are well known to get leaky after some time and might fail. Original part number is 152-0400-00 (MB2501), and a good replacement would be to use MUR160 600V 1Amp 50nS diodes (Mouser PN 821-MUR160).

Oh, and in case its not obvious to someone, DO NOT use common 1N400x series diodes as a replacement for this application, they are way too slow and will not work in this case that requires fast switching. MUR-160 or any 1Amp and 200-600PIV equivalent fast switching diode will work just fine.

The LV power supply board is located in the middle of the scope and can be accessed by temporarily removing the top board that you will see when you open the scope. While you have that board out you might as well closely examine all the electrolytic caps for any sign of leakage. Or you could just replace the usual ones and be done with it, as sooner or later you will have to deal with this.

And finally, while you have access to the big main board, check the voltage on the Lithium battery and see if it might need replacement. Anything under 3V is suspect. Fortunately in these scopes that battery does not back up any critical calibration constants, it just allows the scope to boot up with the same configuration that you used before shutting down.

-----------


Dave Wise
 

Would UF4005 be okay? (Fast-recovery version of 1N4005.)

Dave Wise

From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of tekscopegroup via groups.io
Sent: Thursday, June 24, 2021 10:19 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] New (old) 2247a enquiry

The highest priority preventive repair for any of the 224x scopes (2245, 2246/A, 2247A, and I am not also sure if the later model 2252 also requires it as well, is to replace all the rectifier diodes on the LV power supply board (total 17 diodes) that have either ZM or ZS marked on them as they are well known to get leaky after some time and might fail. Original part number is 152-0400-00 (MB2501), and a good replacement would be to use MUR160 600V 1Amp 50nS diodes (Mouser PN 821-MUR160).

Oh, and in case its not obvious to someone, DO NOT use common 1N400x series diodes as a replacement for this application, they are way too slow and will not work in this case that requires fast switching. MUR-160 or any 1Amp and 200-600PIV equivalent fast switching diode will work just fine.


Phil Wong
 

-----Original Message-----
From: TekScopes@groups.io <TekScopes@groups.io> On Behalf Of Dave Wise
Sent: Thursday, June 24, 2021 1:41 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] New (old) 2247a enquiry

Would UF4005 be okay? (Fast-recovery version of 1N4005.)

Dave Wise

From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of tekscopegroup via groups.io
Sent: Thursday, June 24, 2021 10:19 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] New (old) 2247a enquiry

The highest priority preventive repair for any of the 224x scopes (2245, 2246/A, 2247A, and I am not also sure if the later model 2252 also requires it as well, is to replace all the rectifier diodes on the LV power supply board (total 17 diodes) that have either ZM or ZS marked on them as they are well known to get leaky after some time and might fail. Original part number is 152-0400-00 (MB2501), and a good replacement would be to use MUR160 600V 1Amp 50nS diodes (Mouser PN 821-MUR160).

Oh, and in case its not obvious to someone, DO NOT use common 1N400x series diodes as a replacement for this application, they are way too slow and will not work in this case that requires fast switching. MUR-160 or any 1Amp and 200-600PIV equivalent fast switching diode will work just fine.


Richard Merifield
 

Great, thanks. I can access these articles-37 diodes conveniently

https://www.jaycar.com.au/diode-sf37-600v-3a-d027-pack-10/p/ZR1090?pos=12&queryId=8d18e5369eae728d1aa35a1416d10e86&sort=price-desc

They appear a suitable choice ?

Regards

Richard


tekscopegroup@...
 

On Thu, Jun 24, 2021 at 10:40 AM, Dave Wise wrote:


Would UF4005 be okay? (Fast-recovery version of 1N4005.)

Dave Wise
UF4005 or 1N4936 both should work fine. Any 1Amp 200-600PIV fast switching diode will work.


Richard Merifield
 

I have noticed the traceand cursor lines dip down slightly from left to right. They have a slight curve to them. Is there an adjustment that can be made to fix this easily ? The service manual is a little overwhelming.

Regards

Richard


tekscopegroup@...
 

If nothing else, sounds like you need to perform the trace rotation which is a screw trim adjustment which can be accessed from the front panel between the Focus and Readout control knobs just under the CRT face. That adjustment should allow you to get the trace even with the "horizon". If there is also any "bowing" on the trace you might need to perform the Geometry adjustment first, which as far as I remember is inside the scope. I don't have the SM manual handy so best you take a look into it. Manual is available here:

https://w140.com/tekwiki/index.php/2247A


Richard Merifield
 

Thanks, that fixed it. Bit embarassing, should have read the user manual before looking at the service manual.