Products > Test Equipment
Tektronix 2235 repair thread
lowimpedance:
I recently had both a 2235 and a 2235A open on the bench and one significant physical difference is the switching transistors heat sink on the non 'A' version is only around a third the size of the one in the 2235A. And when running these heat sinks get very hot indeed. Also noted while looking up info on these old timers that there is provision for a fan and some people have retrofitted one successfully. Although they did not indicate which direction the air flow would be ???. I guess that would be inwards?.
David Hess:
Tektronix used a couple of different configurations to power the fan when it was included. It is 13.6 volts on the 2236 and 8.6 volts on the 2230 and 2232. The older fans used the custom brushless DC motor shared with other older Tektronix instruments with a really impressive looking and performing impeller. At some point they changed to using a standard tubeaxial fan.
The fans on my 2230s and 2232s blow outwards but if I installed one from scratch, I would probably configure it to blow inward with a dust filter on the outside.
I think what happened is that Tektronix did a "final" design of the 2 channel 22xx series with the 2235A, 2236A, and early 2232 released in 1990 where as many assemblies were shared as possible. The 2235 and 2236 were the oldest models of the 22xx series so they brought them up to the standard of the "new" 2232. The 2213 and 2215 do not count as the oldest because they were more like prototypes and quickly replaced by the 2213A and 2215A which came out *after* the 2235.
TERRA Operative:
I made my fan blow inwards, easy to filter and it blows air directly onto the hot bits.
Tek specify a 20ohm resistor, but I used a 10ohm IIRC to adjust the speed of the fan I used.
I made a thread about mine, and a video, I managed to cross reference the parts in the Tek service bulletin to modern parts and mine is working well.
I didn't swap the line filter module yet, but I found a shop selling TDK-Lambda brand filters for about $10, so I might grab one and stick it in.
Links below for reference:
https://www.eevblog.com/forum/repair/tektronix-2235-upgrades/msg1862394/#msg1862394
I'll be following this thread for further upgrades, I can't help tinkering where I shouldn't... :-/O
floobydust:
I don't think the Tek pre-reg PSU is properly understood. It looks like a flyback converter but has a resonant winding/cap C908, I think for low EMI.
The TL594 oscillator might have to be bang on. But the components differ in models:
2215: R920 20k + 1800pF C920 27.8kHz?
2235: R919 11k + 1800pF C919 50.5kHz?
2235A: R918 was hand-picked for frequency, not sure of the target.
I would rather have the supply working properly instead of adding a noisy fan. I like a silent scope.
I did make a mistake and replace C908 with a part 10X bigger 2,200pF, the PSU MOSFET ran much hotter.
bd139:
Yeah I don’t want a fan in this. My main digital scope is a TDS210. Another silent item. The TDS210 actually replaced my DS1054Z because it was quieter and did the job fine! I was hoping to have the TDS210 and 2235 on the bench and leave it at that. Get rid of the other four scopes! :)
2235 targets 60Khz apparently. I was wondering if the frequency was related to loading. Higher loading, higher switch frequency.
I have all the parts in now to fix the power supply however this might not happen until the weekend due to other things I need to do.
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