My $35 TDS460 Oscilloscope Repair Project

[Smoky]

[andy3055]

Looks promising!

[Smoky]

Thanks Andy!

I would classify this particular TDS460 as their "base" model. It's not loaded with any of the extra options like FFT, RS-232/Centronics, etc. I detail these scopes to the max! From the inspection of every trace down to the polishing of every screw. I take great pride working on this American-made equipment!

Ultimately, my goal was to have one extra TDS oscilloscope for "high-voltage" measurements, but now I have three! Last year, my Sencore SC-61 oscilloscope kicked the bucket. With the Sencore 10x Lo Cap probes, I could measure up to 3KVDC. For some reason, the digital read-out on the SC-61 started flashing, and without warning, it stopped working all together.

Since my passion is working on mono tube amplifiers, I was put out of commission. Here's one of two Six Pac mono audio amplifiers that I recently restored.

Two weeks ago, I made an offer on a brand new Tektronix probe. It's a P5100. What was a plus too was that the cover of the package had the same color scheme printed on these older TDS scope's users and service manual binders. Anywho, the seller accepted my offer.

The P5100 is rated up to 2500VDC and it's not big and clunky either. I'm going to use this probe with one of the TDS420's on a separate bench in my garage. I also own a P6009 100x probe that is good to 1500VDC. I'm also going to buy a nice differential probe package too as I learn more about this electronics stuff

Here's a look at my next mono tube amplifier repair project. Cary Audio CAD 211 FE's. The B+ averages around 1380VDC in these things. I traded labor for them a few years back 

[andy3055]

You seem to spend a lot of time on these. I used to do the same when I was younger. But since moving to the US,  I have not done much. Most people I know have the more modern stuff. The only person I know who has a hybrid amp is one of work friends who bought an Ampeg SVT 4 last year from a swapmeet. That is the one I fixeed for him and busted the scope by leaving it on overnight accidentally. I just finished fixing the scope a few days back.

[andy3055]

BTW, what did you use to clean the boards in that scope?

[Smoky]

It all started when a professor from NC State gave me his non-working TDS420 three years ago!

I have a ton of classic audio equipment and I needed to learn how to use an oscilloscope. So what better way to learn electronics than to fix the oscilloscope you intend to learn from

I scrub the PC boards with Dawn dish-washing detergent and used an air compressor and a heat gun to blow them dry.

The #1 problem that I have found after restoring these three scopes is the way the traces will rot under the SMD's when the electrolyte streams down the board.

If you find a crusty solder joint, scrape it down to the pad. Flux it and let it boil-off. Clean with alcohol and inspect it. Chances are, the pad has lost continuity. Tin/repair.

Over the weekend, I couldn't resist buying this on Ebay:

https://www.ebay.com/itm/Tektronix-671-1685-11-Acquisition-Board/174009826066?hash=item2883cb3b12:g:R0EAAOSwlkFdZB1t

It is the exact same Acquisition board that's in this TDS460, part number and version. Shipping costed more than the board!

It looks to be a very good condition too.

...with all of the leftover parts that I have, I guess another TDS460 is in my future 

Btw, here's a P6101 probe attached to the probe compensation post on the rebuilt TDS460.

I also put a square wave into it from the Siglent waveform generator.

...and here are the three Tektronix scopes that have been meticulously restored. Two TDS420's and one TDS460.

Here's a test that I performed on the three at the same time. All were warmed up and SPC was executed. I limited bandwidth on all three scopes to 20mHz and 20.0 MS/s. The Siglent waveform generator was set to a Sine wave of 15Hz at 2Vrms.

All three scopes read 15Hz on all 4 of their channels. The frequency would bounce around slightly but the center measurement was 15Hz.

The voltages:

TDS420, Serial #B021008

Ch 1, 1.980
Ch 2, 1.982
Ch 3, 1.982
Ch 4, 1.982

TDS420, Serial #B020953

Ch 1, 2.004
Ch 2, 2.004
Ch 3, 2.004
Ch 4, 2.000

TDS460, Serial #B021375

Ch 1, 2.002
Ch 2, 2.000
Ch 3, 2.008
Ch 4, 2.008

[andy3055]

Thanks for sharing the story. Very nice work!

[james_s]

I would classify this particular TDS460 as their "base" model. It's not loaded with any of the extra options like FFT, RS-232/Centronics, etc. I detail these scopes to the max! From the inspection of every trace down to the polishing of every screw. I take great pride working on this American-made equipment!

Nice to see I'm not the only one who does that. I've restored about half a dozen Tek DSOs of various series, they always clean up real nice. I'm a big fan of the older Tek scopes, the TDS700 and TDS3000 are my favorites. One of these days I still need to get out my TDS460 again and see if I can solve the SPC failure, that's the only remaining issue it has.