Repair broken Tek 485 or buy good used 2465/A/B?

The 485 is a really excellent scope, and the problem you describe should be fairly easy to repair. There's no sense in upgrading, as a beginner you probably won't use a large portion of the features the 485 provides even.

I had the same problem with my 485. Took me a few hours to isolate (due to the disassmebly required) but it was caused by a shorted tantalum cap. I used to fix T & M equipment for a living, so I may be more adventurous than you. The 485 is a classic, probably the best portable scope ever made. I bet if you got your head and hands in the 485 you could find and fix the problem.

Good luck

--
Mike McGinn		
"more kidneys than eyes"
Registered Linux User 377849

snipped-for-privacy@gmail.com wrote in news:8617845e-5625-4187-a7df- snipped-for-privacy@n20g2000hsh.googlegroups.com:

at least with pots,you can always sub something in.

the 2445/65 series was the best portable scope TEK ever made. BUT,because TEK stopped making their custom ICs/hybrids,they had to stop making the scopes.There's also a problem with failing horizontal output amp ICs(A TEK-made IC).

Not if you can get the parts for the 2465,and have a service manual. ;-)

"robust"?? the 2445/65 was better built,IMO.

*IF* you got a fully working 2465 for what the 485 cost to repair,I'd go with the 2465. then look for a 2nd for parts support.

the one thing that worries me about your 485 is the attenuator HF switch contacts;they lose tension,and the white plastic cam follower that holds the gold contact to the spring arm degrades over time,to the point the contact falls off. you can't get them anywhere except from salvaging a dead scope. Intermittent attenuators were a very frequent problem with the 485.

One note;the 2445/65 sometimes came with Options that have separate op and service manuals;there will be a sticker on the rear denoting what options were installed,if any.Stuff like counter/timer,TV trigger,DMM,and a RARE word recognizer option.I never saw one of those.

--
Jim Yanik
jyanik
at
kua.net

I agree 100 percent.

My first guess would be one or more of those imfamous tantalum gumdrop caps have decided to turn into short circuits. These are on the power supply PCB on the bottom. Save yoursefl some grief and replace them all (maybe 2 dozen). I have just been putting in aluminum electrolytics. Not sure how much difference it makes.

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Or can I just stick with tantalum replacements? Mouser shows some, though I have no idea values.

*tantalum*&Ntx=mode+matchall&Ns=P_SField&Mkw=tantalum&N=1323038%203805535&Ntk=Mouser_Wildcards

I assume radial termination style?

You say you've been putting in AL 'lytics. Do tants come polarized?

Say I go with Nichicon AL 'lytic radials. Is there a preferred series? They have all kinds...

Agreed, and I bet a nickel the issue is that there is too much dust and dirt providing leakage paths in the high voltage section. Have the tech give it a good cleaning and you will probably be fine.

I'm still using a Tek tube scope at work and it's always been flawless although the calibration guys hate me.

--scott

--
"C'est un Nagra.  C'est suisse, et tres, tres precis."

[snip]

Stay away from the 2465A/B at all costs. Some time during the production of the A series, they sold the hybrid operation. Quality of the hybrids dropped precipitously, leading to a near 100% failure rate. These hybrids available only occasionally at extreme cost. The 2465 also has cooling problems.

The original 2465 is better, but spares are still a bitch.

Regards, Bob Morein (310) 237-6511

be

Hi James. I had a 485 many years ago to use for field work ( not that easy schlepping it around the country). I think it had a 250 MHz bandwidth. It's really packed so be careful when attempting repairs. Starting with checking the low voltage power supplies is a good idea. Also be careful if sending it out prepaid for service. Check the service place thoroughly for references and for viable guarantees. The 485 is a professional scope that way exceeds the hobbyists requirements. So if you can repair it reasonably, you will own a classic gem.

Cordially, west

>

"West" wrote in news:OQ53j.37950$Xg.23109@trnddc06:

if you ship it anywhere,**pack it very well**,with at least 3-4 inches of padding on EVERY side,top,and bottom.

Using loose peanuts is a great way to have your scope smashed up. Better to pack the peanuts in plastic bags,making "pillows" and place those around the scope.

I've seen plenty of poorly packed instruments,and UPS/FedEx/DHL/USPS is not liable for poorly packed items.

--
Jim Yanik
jyanik
at
kua.net

I'm an expert on these things. The 485 is the best portable analog scope ever made. It is arguably the best analog scope ever made, though the 7904 series competes well on the bench. Do anything you can to keep one working. There is no substitute for a 485/7904, and I've used them all, including $50,000 digital ones. For repairing analog electronic oddities, digital frequently simply doesn't work.

A 485 is 350 MHz scope.

The 2465 is a very poor substitute, though a good scope.

Doug McDonald

Hi Doug,

Thanks for your thoughts.

Do you do repairs on these scopes? Or does anyone in the group know some noteworthy techs I can send my scope to for repair?

It seems most here think I should just stick with the 485. I have no problem with that. However, it's good that I brought this thread up as now I've learned that there may be issues with the 485 to be concerned about, namely the attenuator problem Mr. Yanik has brought up (that is somewhat disconcerting).

BTW, how long do the CRTs last on these scopes?

Doug McDonald wrote in news:fiku3a$bjf$ snipped-for-privacy@news.ks.uiuc.edu:

Oh?

IMO,the 485 is much worse than a 2465,having lots of flaky attenuator problems,a bitch of a power supply repair-wise,and less accuracy than the

2465 series.And you get a better CRT display with the 2465. The 2465 was the best portable scope TEK ever made.What killed it was TEK selling off the ICO/Hybrid plant to Maxim,and Maxim cutting TEK's throat by forcing a last-time buy on TEK-made ICs. The 485s are getting really old,the HF switch contacts are degrading and unavailable. The 2465 is more serviceable -if you can get the parts. the 485 has the same problem.

I worked for TEK for 21.5 years in their Field Service centers repairing and calibrating these scopes.I'd much rather work on a 2465 than a 485.

485s were a PITA even when TEK was still issuing the mod summaries on fiche.There were SO many ECO changes,you couldn't keep up with them all.

I agree about the 7904 lab scopes being great.Had one on my bench.

--
Jim Yanik
jyanik
at
kua.net

snipped-for-privacy@gmail.com wrote in news:fc628060-369a-4006-8372- snipped-for-privacy@e23g2000prf.googlegroups.com:

Too many variables. How long does a light bulb last?

--
Jim Yanik
jyanik
at
kua.net

I no longer recommend owning or using Tektronix analog scopes, period. Yes, they were very well built, but none of them are 100% supported and they all lose the same parts. The hybrid issue is a big one, but CRTs, attenuators, and high voltage parts on all solid state Teks are getting unavailable even through the back channels.

If some company decided to FULLY SUPPORT certain Tek models, guaranteeing availability of every part from new production-or at least every part that is getting scarce-I'd say yes.

Ironically you can still get every possible part for many tube Teks, but the size, weight, power draw and heat make them nonstarters. That is why the parts are available.

Buy a new scope.

New scopes are expensive, used Teks in good working order are relatively cheap and still offer excellent performance. There's millions of them out there and parts units can still be found. If you're a business with budget to burn then yes, buy a fancy new scope, but if you're a hobbyist on a budget, you can't beat an old Tek.

There is only one problem: there are no "new scopes" that will substitute for a 485/7904 for some purposes of work on analog signals. Period. They don't exist.

We don't know what the use of the original poster is supposed to be. The "have to have analog" ones generally involve visual detection of rare events in analog signals. The dead time of fast digital scopes can cause hopelessly great "down time fraction" for this.

For most purposes digital scopes are fine.

Doug McDonald

I agree 100%!!!!!!!! Buy a brand new chinese scope with no support, and throw it away when it dies. Repeat till you're tired of using crap, then buy a used US made scope.

--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida

See my original post:

"In the past, I have serviced tube amplifiers for friends. Right now I have a 3M (Mincom) M56 professional multitrack tape recorder I am currently in the process of aligning."

Probably going forward, much of the same.

Jim Yanik a écrit :

Totally agree on the 2465.

As for the DSOs, the OP clearly don't know what good ones can do. See the DSA/11k plugins series. That's simply the best scope I've seen. Period.

I currently have a setup with a DSA and one 11A34 and one 11A33 diff plug-in from which I *measure* signals at the 10uV level with excellent accuracy (has been checked against some calibration tooling). But the truely amazing parts are the plug-ins (11A33 & 11A34 checked) recovery from deep saturation. Right now after a 200mV step down to 0V (on a 1mV/div scale), both plug-ins show not more than 40uV thermal tail and recovers from saturation in under 50ns. All this being very well behaved and hence can be well compensated for, pushing the performances one step further.

We're trying to find a 'modern' DSO doing that: nada, nothing. The last we've tested (DPO7054 @ euro 15K) showed near 2mV thermal tailing after a 200mV step.

What I wonder is what did make Tek losing the art of those exceptional input stages...

Now, try to do this with a 485 or a 2465. And no, a 7K series with a

7A22 PI can't do that either (too much drift and not enough BW).

--
Thanks,
Fred.