I was doing some tinkering last night when the big cap on my 2235 scope PSU blew
up: bad smelling smoke, and browny electrolite made its way to the IEC socket _
external side (bottom).
I switched it off as soon as I heared the fatidical (fffffft!) sound and hinted
the smoke.
Apart from that, the CRT side wall of the scope felt medium hot, though I
don't know if that's normal.
Do anybody knows if blown PSU caps take away other components when they
fail? I inspected the surrounding area but didn't see any obviously failed-
looking components. And I saw tons of protection devices on the circuit... It
would be certainly a ton of luck that the problem was just an aging capacitor
(marked 1NE30 dunno what date is that) and solved by its simple replacement...
any opinion?
I bought it used on December (from USA, I live in Spain). I opened and
inspected it when i got it and was marvelled at its shape and clean layout,
there were no signs of repair, and everything looked nice and clean.
up: bad smelling smoke, and browny electrolite made its way to the IEC socket _
external side (bottom).
I switched it off as soon as I heared the fatidical (fffffft!) sound and hinted
the smoke.
Apart from that, the CRT side wall of the scope felt medium hot, though I
don't know if that's normal.
Do anybody knows if blown PSU caps take away other components when they
fail? I inspected the surrounding area but didn't see any obviously failed-
looking components. And I saw tons of protection devices on the circuit... It
would be certainly a ton of luck that the problem was just an aging capacitor
(marked 1NE30 dunno what date is that) and solved by its simple replacement...
any opinion?
I bought it used on December (from USA, I live in Spain). I opened and
inspected it when i got it and was marvelled at its shape and clean layout,
there were no signs of repair, and everything looked nice and clean.
you can get a service manual from www.w7fg.com -- the cause is probably not just the capacitor itself -- did you have adequate ventillation.
markp said:
highly unlikely that "old age" afflicted a 2235. sometimes the power supplies in the TEK scopes of 2XXX series will go out due to heat stress. that's why I asked if there had been adequate ventillation.
the 22XX series of scopes are still repairable, but they are so inexpensive ($200 - $400) it hardly seems worth the effort unless you are going to do it yourself.
I didn't expect that amount of replies in such a short time! you guys are great 
Now the answers:
* It died after an hour of so of work, not on power on.
* It had adecuate ventilation, this is a portable scope, and it was placed at about 30 degrees to the flat surface (table) it was laying on (handle bar below chassis).
However, the PSU side of the chassis was only slightly warm; where temperature was certainly above the rest was on the rear CRT side.
* It had an appropiate (I'd swear still the original) fuse.
I'll try to check the rectifiers and will replace the cap.
Are the tek service manuals worth? Are they simply schematics or do they include troubleshooting procedures, etc?
Now the answers:
* It died after an hour of so of work, not on power on.
* It had adecuate ventilation, this is a portable scope, and it was placed at about 30 degrees to the flat surface (table) it was laying on (handle bar below chassis).
However, the PSU side of the chassis was only slightly warm; where temperature was certainly above the rest was on the rear CRT side.
* It had an appropiate (I'd swear still the original) fuse.
I'll try to check the rectifiers and will replace the cap.
Are the tek service manuals worth? Are they simply schematics or do they include troubleshooting procedures, etc?
what!?!? that makes a ton of sense! I couldn't see goop on the PCB, and I wondered how in earth could the goop reptate to the IEC socket and reach out without leaving traces near the cap.
Also, what I was doing was measuring back EMF from electric motors to determine achieve RPM, could that be the thing that aided in frying the IEC?
This scope has "lived" always in the US, and I have used it here in Europe only a dozen times... so what you say makes a lot of sense. I wish!!!
When you say "IEC EMI filter" you mean the whole IEC socket? or is the filter detachable?
I happen to have some spare IEC sockets including filters at hand...
Also, what I was doing was measuring back EMF from electric motors to determine achieve RPM, could that be the thing that aided in frying the IEC?
This scope has "lived" always in the US, and I have used it here in Europe only a dozen times... so what you say makes a lot of sense. I wish!!!
When you say "IEC EMI filter" you mean the whole IEC socket? or is the filter detachable?
I happen to have some spare IEC sockets including filters at hand...
The main power supply in the 2235 is a switching type. Those supplys are more likely to blow the switching transistors out long before a capicator drawing alot of current would fail. Parts are difficult to get for any CRT based Tektronix scope as Tektronix discarded all of their spare parts to the surplus makets a number of years back. Buying another scope of the same model number os about the only way to aasure yourself parts availability. There also a few places on the net that specialize in spare parts for test gear and probably the largest is Sphere up in Canada.
http://www.sphere.bc.ca/test/index.html
Mark
P.S. I forgot to mention that in repairing TEK scopes and many others such as H-P and Fluke the main problem is lack of availability of the many custom I'C's that were used in them. These are not re-labeled I'C's but actually custom designed and manufactured by Tektroniz and others. These Chips, some are hybrids, allowed them to meet or exceed the published specifications and manufacture test equipment using normal assembly line production methods. Most TEK scopes far exceed their published specs. My 465B is good to about 150 mhz!
http://www.sphere.bc.ca/test/index.html
Mark
P.S. I forgot to mention that in repairing TEK scopes and many others such as H-P and Fluke the main problem is lack of availability of the many custom I'C's that were used in them. These are not re-labeled I'C's but actually custom designed and manufactured by Tektroniz and others. These Chips, some are hybrids, allowed them to meet or exceed the published specifications and manufacture test equipment using normal assembly line production methods. Most TEK scopes far exceed their published specs. My 465B is good to about 150 mhz!
The IEC socket at the back of the 2235A is actually an EMI filter. I opened the case, unscrew the filter, desoldered the 3 mains wires, threw out the filter, and wired directly to mains. Switched it back on and it worked.
When I bought it used, I was cautioned to use a step down transformer to 110V. I forgot about it and about half an hour or so after switching it on, there was this hissing, smoke and blackish brown mess bubbling out of the IEC socket. I wasn't even measuring anything, just powering it up.
A friend of mine also bought the 2235A the same time. He ran it off a step down transformer (110V) and no problems. Seems the EMI filter doesn't like 240V. Strange.
Mark A. Gulbrandsen said:
I have used the fellow whose email address is: oscilloscopes@aol.com to get some spare parts. ( a crt for a 2215) he also repairs scopes -- but he's in California.
Not to argue but, dealing with 1000's of Tek waveforms and vectorscopes everyday it is very common to have a PS cap die on power up if the unit had been running for years without being turned off then turned off and re-powered(after being moved etc). The electrolyte in the cap collapses when power is removed and it has dried out over the years. I agree the custom sip IC's are hard to find but they are rarely the culprit. Bridges go but not that often, then the switching transistor after that. More ofter the stupid power switch will break or the shaft will bend so it doesnt push hard enough.
mcp, I owe you a beer!! It was the IEC socket. I happened to have a spare, replaced it and... voila! I got my scope back! 
I wouldn't have thought in ages it was the IEC socket, I've never seen a IEC to smoke and spread electrolyte in my life... the fact the electrolyte made its way to the outside was even more puzzling to me. Is that electrolyte? Do IEC filtered sockets contain it??
I haven't tested the scope thoroughfully yet, but after a couple of quick tests it seems to be fine. I guess that was the only component that could burn without taking away more components!
BTW if these scope series suffer from heat stress, its is advisable to aid the PSU cooling actively? i.e. adding a fan? there seems to be a place for placing one, but I'm wonder if it would induce noise?
thanks again to everyone!
I wouldn't have thought in ages it was the IEC socket, I've never seen a IEC to smoke and spread electrolyte in my life... the fact the electrolyte made its way to the outside was even more puzzling to me. Is that electrolyte? Do IEC filtered sockets contain it??
I haven't tested the scope thoroughfully yet, but after a couple of quick tests it seems to be fine. I guess that was the only component that could burn without taking away more components!
BTW if these scope series suffer from heat stress, its is advisable to aid the PSU cooling actively? i.e. adding a fan? there seems to be a place for placing one, but I'm wonder if it would induce noise?
thanks again to everyone!
2 pukka:
No, heat stress is rarely known. No fan needed (except you live in a desert like area).
But if you want to do your 2235
(and 2213/2215/2213A/2215a/2235A, if others read this thread)
some real favour
: Once the little "cage" containing the psu is opended, look for the FET in the SMPS, a small TO-220 cased one with a withish/brownish plastic "molex" connector connecting S, D, and Gate. 
Cut off the molex, and solder the wires directly to the FET.
Reason: The molex weakens during the years. contacts get worse, heat builds up. Sooner or later the plastic turn to charcoal. This fries the circuit, most often the FET. sometimes more (Gate resistor TL594 switchmode IC on the board, etc.)
Done this on almast 20 of these scopes (all failed with FET and molex)
Al the best with your 2235 - it's a real well designed scope, and a perfect analog workhorse!
No, heat stress is rarely known. No fan needed (except you live in a desert like area).
But if you want to do your 2235
(and 2213/2215/2213A/2215a/2235A, if others read this thread)
some real favour
: Once the little "cage" containing the psu is opended, look for the FET in the SMPS, a small TO-220 cased one with a withish/brownish plastic "molex" connector connecting S, D, and Gate. Cut off the molex, and solder the wires directly to the FET.
Reason: The molex weakens during the years. contacts get worse, heat builds up. Sooner or later the plastic turn to charcoal. This fries the circuit, most often the FET. sometimes more (Gate resistor TL594 switchmode IC on the board, etc.)
Done this on almast 20 of these scopes (all failed with FET and molex)
Al the best with your 2235 - it's a real well designed scope, and a perfect analog workhorse!
2 pukka:
No, heat stress is rarely known. No fan needed (except you live in a desert like area).
But if you want to do your 2235
(and 2213/2215/2213A/2215a/2235A, if others read this thread)
some real favour
Cut off the molex, and solder the wires directly to the FET.
Reason: The molex weakens during the years. contacts get worse, heat builds up. Sooner or later the plastic turn to charcoal. This fries the circuit, most often the FET. sometimes more (Gate resistor TL594 switchmode IC on the board, etc.)
Done this on almast 20 of these scopes (all failed with FET and molex)
Al the best with your 2235 - it's a real well designed scope, and a perfect analog workhorse!
hey tekman
i got a trek 2225 working great except the trace rotation pot, i haven't seen it on service manual, any thought on how to fix it?
regards wolf
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