A few weeks ago my Tek 2245A 4 channel 100Mhz scope stopped working, I have the manual so thought it might be a straightforward fix. Now although I have used all sorts of Tek equipment for many years, the only thing I know about their repair is that by the time its does go wrong, it's usually ready for the skip and they have very complicated power supplies.
I've attached a photo of the circuit, all the primary side capacitors were replaced as they were dried out, high ESR. The PSU consists of a two part regulation system, a "pre-regulator" chopper which produces a regulated 44V DC supply to run an "inverter" which provides the secondary supplies through a transformer which also isolates the mains. The pre-regulator works OK the 44V rail is present but a bit low at 41V, but reading the circuit description this is probably due to there being no load. I've checked all the components in the secondary "inverter" but it just will not oscillate, the only items not checked are the transformers, but I've measured them as best I can and they don't look to be faulty and aren't that highly stressed by high voltage, the CRT anode is supplied by a doubler module from a 2.7Kv pulse. I've checked all secondary rectifiers and capacitors and I'm fairly confident the fault does not lie there. I say fairly confident, because since looking at various sites on the internet regarding repair of this type of scope, lots of people suggest that some diodes can become partially leaky but measure OK, of course many suggest carpet replacement of most components, but I don't fancy that.
Does anyone have any suggestions ? I've tried it on load, off load, dummy loads etc, and if it wasn't for such a variation in the required supply rails I'd have a go a building a replacement from modules, the high voltage circuitry has been disconnected and checked and I've even used an external 44V DC supply (as suggested in the manual) and it still won't work !
These scopes are available second hand and of course the modern Chineese offerings are good value, but I like this scope and know how to use it and would like to see it work again.
I suspect you've already found these two threads, but in case not, perhaps they might be of use.
https://www.eevblog.com/forum/repair/dead-power-supply-in-a-tek-2245a/
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/
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If it proves to be a real pig to fix (like the timebase board can be) then I can thoroughly recommend these people in Rhodes - Dinos is very helpful and friendly.
https://www.qservice.tv/vpasp/shopdisplaycategories.asp?id=28
Thanks for the replies, I had found the first EEV forum post when I first had the fault, however re-reading the full thread it seems the symptoms are exactly the same as mine, which leads me to the conclusion that the flyback transformer is faulty, it is available for $44 shipped to the UK. If I order one I'll keep everyone posted.
Could a rewind be easier/cheaper? There are several guys who will rewind, Ed Dinning and Mike Barker to name 2 on the BVWS membership list.
Boater Sam
I had three tek scopes given to me a few years ago - all had handwritten labels on "Not designed to be repaired - scrap" - obviously a disgruntled engineer! I managed to get them going and passed them on. On the day job, I still have a 2252 , which occasionally acts weird when first switched on, as one trace is always miles off view, but a quick twiddle of the position knob gets it sorted, and it sill performs ok.
My own 2252 I passed on about 15 years ago, which I regret, as I'd bought a Tek LCD 'scope (model escapes me). The LCD is still working well today.
I have a 2445B which developed a timebase fault and the board was subsequently sent off to QService - who fixed it. Amongst other faults was the dreaded Dallas NOVRAM. Dinos at QService did recommend going through the PSU on it, which I am yet to do.
Life has got in the way.
