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Apparently not... I didn't have a schematic on hand for the 2225, and assumed it would be similar to other scopes that tek made with triplers. But, the 2225, being the economy model, is not exactly a

Easy support for DC operation makes more sense than what I originally thought which was that Tektronix got tired of the problematical 2235 design. Plus the 2247A series and then the 24xx series

Huh? Are we talking about the same oscilloscope? The 2225 (and the 2235 series) does not rely on any feedback between the high voltage outputs for the CRT and the regulator or at least I do not see

I suspect the design rationale for the 2225 being how it is was is that it supports a low voltage DC input as option 07 (not fitted to mine) as well as line voltage. Ergo they picked an intermediate

Chuck, Thanks for the advice on the 494AP. Thankfully mine is in good working order. All of the caps in the power supply have been changed just as you suggested and the fan is running as it should. It

If you have a 494P with problems, let me suggest that a prophylactic replacement of all of the power supply electrolytic capacitors is a very good idea. The 494 family has a very high number of watts

Gang, I rarely say much on this forum, but I lurk a lot and always learn things from your adventures. It really pleases me to know that you do not toss these jewels in the e-waste like some do. I have

Thanks Chris, That is a nice looking scope you have so it's no wonder you put the effort into repairing it! We all learned some new things through the kindness of Chuck Harris and other members. Your

The 2225 HT consists of the inverter transformer with a separate wired tap (rather than via board) which flies out straight to the multiplier which is a good inch away from everything. No spark gap

I think you are correct. Hopefully, the bad capacitors were allowing the HV to go way, way higher than normal operation requires, and any arc-trails will be a non issue. Depending on how you removed

The locations of the C953 and C983 capacitors you changed today, fits directly into the 'power supply losing regulation' line of thinking. Plus you have regained proper control over the CRT with the

Indeed we did learn from Chuck (thanks Chuck!). I shall refrain from doing that in future. I suspect the original issue was the power supply losing regulation or oscillating and providing a slightly

Hi Chris, I'm happy to hear that the arcing problem was resolved, and that your 2225 has been restored nicely. In a couple of hours this morning it went from bad to good in a way that I don't

Turns out I was being an idiot. I had missed replacing four capacitors: C915, C914, C953, C983. The last two were Philips axial 030's which are notoriously problematic. I replaced them with some

When the multiplier is disconnected, so is the HV sensing resistor chain used for feedback. The disconnected sensing resistor chain tells the control circuit that the HV is lower (zero) than the

Just to add, it only consistently arcs when the multiplier is disconnected. If you leave it connected it arcs on startup for a few seconds and momentarily on shut down and occasionally when running

Well it looks like bad news. I replaced all the capacitors and that has solved a number of ills with the rails. Nice stable DC coming out now with virtually no ripple. Display is nice and crisp (when

Indeed. It's a rather safer design although you still have the be careful because the inlet board and HT are very close to the main switching converter so no live probing in that department. There are

The 2225 switching power supply is one of the very rare exceptions to this and is not an off-line switching power supply. The input to the switching power supply is isolated from the line by a 60 Hz

I don't really know about the Tektronix power supply, but I had a similar problem a few years ago in my IFR-1500 Communications Service Monitor. In the IFR power supply, and I believe this is true for