Author Topic: First Scope: Tek 2445  (Read 682 times)

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Offline SynViksTopic starter

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First Scope: Tek 2445
« on: March 26, 2023, 07:51:24 am »
*Edit* As I'm new here I'm not entirely sure if this is the proper sub forum for this thread. Feel free to move it to the correct one if isn't, mods.

Don't really have a pressing need for a scope, but wanted to look at some PWM waveforms and found a 2445 locally for a Benjamin. Came with two P6137 and two P6131 probes, operator and service manual.



Powered up looked at a few waveforms via the test port:





https://youtu.be/QbkXAeunESk

Haven't used an analog scope before but some of the traces seem a bit fuzzy, and as seen in the video some wobble. Also the traces seem to be shifted over a bit such that the horizontal shift knob needs to a bit turned for the trace to be centered. Fan speed seem to be constant for a while but then slowed and varied in speed. CRT focus seemed a little uneven; adjusting focus for the center resulted in blurrier edges.

After using it for an hour heard a pop and disgusting smoke, unit was still displaying a trace but I turned it off pretty quick. Usual suspects in the powersupply board seem to be at fault:



Also removed a seemingly innocent electrolytic from the board and found some nastiness underneath:


Checked several of the larger resistors and found them to be out of tolerance. Common to replace these? How many resistors should I check?


Processing board and motherboard look fine. I tried the "tap on the heatsink" thing for the hybrids but doings so resulted in no observable changes on the CRT, so they should be in good shape:



So a recap of the power supply boards seem to be in order. Seems like it would be a good idea to replace some resistors as well, and I'll have to fix the broken fan shaft collet (what a bizarre design). Big question is how far beyond that should I go? Is there anything on the processing board I should replace?

Also found this note wedged in the service manual referencing PN 119-1445-02 (Digital Attenuator input amplifier). Not sure if this means there's an issue with the CH 2 attenuator, whether it was taken care of... Any thoughts on what kind of symptoms would show if the attenuator amplifier were failing?

« Last Edit: March 26, 2023, 08:40:40 am by SynViks »
 

Offline jonpaul

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Re: First Scope: Tek 2445
« Reply #1 on: March 26, 2023, 01:42:58 pm »
Bravo for the fine post and purchase

Suggest you post all to tekscopes2 and tekscopes @ groups.io

many Tektronix scopes afficanados and ex factory engineers are techs

Use a sig gen to check every range of Vertical V/div to test attenuator

The yellow cracked VDE capacitors at  the power supply input are firebombs  and must be replaced!!!!

bon courage

Jon

An Internet Dinosaur...
 


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