Tektronix 2225 vertical display problem - Page 1
Forum section: electronics / repair

author: AndrewEp17
author_rank: Contributor
timestamp: April 25, 2024, 06:19:27 am
content: Hello, this is my first post. I bought a broken Tektronix 2225 to fix it for fun and the tube works and it has a trace but when I input a signal to either channel it displays a wave form but its barely there. I replaced pretty much every capacitor in it other than a few in the power supply. I checked the voltages and they seem to be correct. But i have to check them again. I think it might be a bad IC or transistor in the vertical amplifier or something and I was wondering if anybody here has any idea of what part would cause this. I included some pictures of channel 1 with and without a 1khz square wave. It doesn't look any better no matter what i change.

author: MathWizard
author_rank: Super Contributor
timestamp: April 28, 2024, 06:28:54 am
content: Hi there, do you have another scope, or signal tracer ? Here's a service manual with schematic's. I'd try and trace the signal into the attenuation/pre-amp section, and then the main vertical pre-amp and driver section.I have no idea what this site is, but the 216page 14MB pdf is too big to upload.http://bee.mif.pg.gda.pl/ciasteczkowypotwor/Tek/2225%20SM.pdf

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: April 28, 2024, 06:37:17 am
content: Possibly a burnt input resistor. Some other guy somewhere here had a burnt input resistor on a 22xx series scope. It's soldered directly on the BNC so not hard to check.

author: AndrewEp17
author_rank: Contributor
timestamp: May 01, 2024, 02:02:04 am
content: Quote from: MathWizard on April 28, 2024, 06:28:54 amI have a rigol ds2302a and I actually ended up fixing it by doing that! I looked at the schematics before but i didn't think of tracing the input signal until you said that haha. i looked at those parts of the schematic and i knew it probably wasn't going to be in one of the preamps because both channels had the same issue. So I ended up tracing it back to Q256 in the vertical amplifier which is the last transistor the signal goes into to drive the deflection plate of the CRT. I removed Q256 and Q257 from the circuit, both were 2N3866. i thought i was going to to have to buy more until i saw that the emitter pin had broken off probably from heat and I tested them with a meter and they seemed to be good so i decided to solder a wire directly to the metal case of the transistors and soldered them to the bottom of the board and that ended up fixing it! thanks for the advice!also i will put them back in correctly i only soldered them to the bottom to test them

author: AndrewEp17
author_rank: Contributor
timestamp: May 01, 2024, 02:05:00 am
content: Quote from: BlownUpCapacitor on April 28, 2024, 06:37:17 ami checked both channels and the resistors are the correct value but one looked a little dark and the paint was chipped so i will probably replace those as well. thanks for the advice!

author: AndrewEp17
author_rank: Contributor
timestamp: May 01, 2024, 02:46:10 am
content: It said the picture was to big for my previous reply so here is a picture of the 2225 displaying a triangle from my function generator

author: MathWizard
author_rank: Super Contributor
timestamp: May 01, 2024, 04:12:29 am
content: Ok well that was an easy fix then. Yeah I like fixing some stuff too, but so far, most problems have seemed pretty straight forward or sort of boring. I guess because nothing had any big amount of damage, like a drink spilled on it.I'm working on a stereo right now, making a schematic. Now it's about time to test the PCBs for issues. Or maybe check some capacitors 1st, it is pretty old.