Restoration of a dumpster Tektronix 2465B oscilloscope :: SunEstra
By the top of June 2023, I got here throughout an attention-grabbing discovering within the dumpster I normally look as much as.
An enormous blue beast was laying there, a Tektronix analog oscilloscope.
I used to be not anticipating to discover a scope in that dumpster as I normally solely discover some pc peripherals and elements after I’m fortunate sufficient.
Nevertheless, this outdated analog scope was there, in fairly fine condition, with its blue probe pocket on the highest, the unique Tektronix deal with, and its entrance cowl.
As soon as I’ve eliminated the entrance cowl, I uncover the unit’s entrance panel, unveiling a Tektronix 2465B 400MHz unit.
A CRT analog oscilloscope from the 90′.
I used to be hooked.
The unit is beautiful, have a look by your self!
With its 400MHz bandwidth, it outperforms my common digital scope Rigol DS1054Z which has a 50MHz bandwidth.
I might use it for particular designs the place high-frequency alerts are used.
For instance, I might consider the standard of digital – sq. – alerts the place my digital scope would have filtered close to basic harmonics frequencies shamelessly.
I needed to take it residence to check it.
On the primary start-up, the scope began blinking on many LEDs of the entrance panel, making relay clicking noises, then obtained caught with a inexperienced LED mild on the ADD mode with nothing displayed on CRT. Wah wah wah wahhhhh…
Possibly it was only a dangerous begin. I imply, trendy units may boot and get misplaced on observe each day.
This time, after placing the scope OFF and again ON afterward, it boots!
However yikes… readout is inconsistent, may seem, after which disappear straight away.
Measured alerts are noisy as hell, even with the GND coupling, the sign appears noisy and shakes across the zero reference.
I used to be skeptical of the scope capability.
After a second reboot, for the sake of certainty, it obtained caught once more into the ADD mode.
After an intense internet search, I discovered many threads devoted to the scope, such because the EEVBlog teardown thread.
Earlier than digging right into a deeper troubleshooting course of when folks had show issues with fading out intensities, step one was to take a look at the grid bias parameter of the CRT.
“The adustment of grid bias controls the depth or brightness of the sample on the face of the tube, simply because the grid bias controls the plate present of an amplifier tube, and at cut-off the sample is totally extinguished”
I first needed to teardown the scope by unscrewing and dragging the scope’s blue case off to entry the CRT grid bias potentiometer. Whereas powered on, I tweak the potentiometer in a single path and observe the adjustments on the CRT. Because the scope had booted into a transparent show and the ADD LED was on, I now perceived a written message on the display screen.
TEST FAILURE 05-40
Yup, one thing was flawed. By studying the scope manual, within the Upkeep part, web page 234, we will learn that the take a look at issues the principle board, as proven beneath.
We acknowledge the habits of the entrance panel with the ADD LED being lit as described within the desk.
The error code 40, which typically turns to 44 on totally different boots, corresponds to Optimistic stage too constructive, no matter it means.
On web page 237, two paragraphs summarize the take a look at case perimeter, as follows:
Because the take a look at checks a number of options, I select to carry out a visible examine of PCBs within the scope.
As I checked out PCBs contained in the scope, I encountered a collection of leaky capacitors on the A5 board.
The A5 board referred to the Management board, as talked about within the documentation.
Two areas on the board obtained leaky electrolytic caps.
Right here is a photograph of the primary space recognized.
As we will see, the leakage appeared to oxide on a number of SMD elements.
The IC with the inexperienced sticker is the DAC talked about within the take a look at examine.
It’d clarify why the take a look at is failing, because the leaky capacitors might need derived {the electrical} traits of neighbor elements, and even broke them.
The identical goes for the second space, as pictured beneath.
The primary space are may be present in C1, the second in K1, as seen on the board structure beneath:
Utilizing this structure, I used to be capable of finding element references on board, which can be helpful to compose the invoice of supplies for the substitute.
A Wiki web page additionally exists for the scope, on TekWiki.
The latter displays many exterior hyperlinks, together with the EEVblog thread and others.
One in every of them is known as 2465B SMD capacitor leak restore, which tells the precise drawback and find out how to restore it.
This leakage is named a plague for this scope collection.
The doc is absolutely good, however don’t match my actual drawback: his areas of leakage are bigger, then I compose my substitute record with an enough invoice of fabric.
After figuring out the leaky caps and contemplating lifeless neighbors, I used web page 305 which is the invoice of supplies of the unique board.
I’ve looked for equivalence of all recognized elements on RS to compose my invoice of fabric for the substitute.
Right here is the BOM in CSV file.
I had typically to exchange 1206 packages with 0804 ones because of lack of alternative.
I changed the aluminum electrolytic capacitors with tantalum ones.
This alternative is debatable, as tantalum might burn, or produce a micro-explosion, unsure whether it is means higher than an electrolyte leakage.
In case you obtained to do that substitute too, take into consideration getting a polymer one.
The electrolytic capacitors that I discovered had a 2917 package deal, uncertain of what was the unique package deal dimension for the leaked capacitors, I select this one as a trial.
To carry out this operation, I’ve upgraded my setup with a hot-air and soldering station: a Yihua 858D and 937D.
I all the time had stationless soldering iron up to now however I discovered it was limiting when it comes to doable operation and extremely irritating.
The recent-air gun will ease the desoldering a part of SMD elements, particularly for built-in circuits.
I carried out the substitute in a single afternoon. After eradicating elements with the hot-air gun and a pair of twizzle, I tidied solder pads with solder wick.
Throughout the course of, I notice that many solder pads obtained away with electrolyte-affected elements, particularly within the first space, as proven beneath. The red-rounded space reveals 2 lacking solder pads for a ceramic capacitor that was extremely broken by the electrolyte leakage.
The little pink arrow reveals my very own mistake whereas eradicating a resistance that was not even to get replaced, ouch!
I had to purchase one other half in 0804 package deal, barely littlier than the unique 1206, so I might resolder it by scratching the hint that go between the 2 pads of the resistance.
After cleansing the areas, it was time to solder the substitute elements.
I began with elements which have contemporary and clear pads.
First shock: rattling, the transistor that I selected is a package deal SOT-523 as an alternative of SOT-23.
I had no alternative on the time, the identical reference was solely obtainable on this package deal, so I believed that it was the identical.
This was more difficult however nonetheless, the SOT-523 packages did match within the SOT-23 solder pads.
One other shock: some solder pads appeared not linked to their traces, because the continuity tester was failing whereas I used to be attempting to solder passive elements.
I recognized a micro-rupture not seen between them, therefore I scratched the hint to reconnect the pad with the hint.
I did the identical for the lacking pads: I scratched the associated hint, tin them, after which introduce the element to solder them.
The result’s fairly as dangerous because the preliminary state of affairs: it should work, however it isn’t elegant. Not an issue.
Tada! Now the scope is appropriately booting and doesn’t fail on a take a look at.
I didn’t carry out any calibration take a look at, so I have no idea how its present calibration is by 2023.
Nevertheless, it seems like this scope has nonetheless some power in its SRAM battery to retailer its calibration values.
That is one other source of problems with this series of scope.
Fortuitously, I would not have to go by way of this in the present day.
