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2465 - impending U800 failure?
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Hello all,
I haven't posted to this list in a long time but have just been lurking, I'm afraid. One of my trusty 2465s has started to give trouble. It's serial number 102481. I bought it used, surplus about 10 years ago and it's had plenty of hard use since, being my daily workshop scope. I've never even undone the case screws - it's Just Worked, and stayed spot-on accurate. I think the tube is a bit tired, since the trace loses focus at high brightness and it's impossible to get the whole screen (corners and centre) exactly in focus at the same time, though it's always been like that and it's good enough. Yesterday, I switched it on to use it, and it came up as usual but after a couple of minutes the entire display, readouts and all, suddenly jumped off the right hand side of the screen and stayed there. I could just about see the left hand end of the trace by winding the horizontal position all the way over to the left, and the scope was clearly still working otherwise: the bit of trace I could see responded to input signals and adjustments of the controls. I noticed also that pressing the 'beam find' button put the display back in the centre, but shrunken as I'd expect. I tried the scope again a little later on and the display came back, but tried it again today and it worked for a few minutes then suddenly jumped off to the right again. I do have the service manual for it, but before I start digging in, are these the typical symptoms of U800 failure? Searching the group, it seems that U800 failure tends to push the display to the left, and I haven't seen anyone document how 'beam find' behaves in that case. Thank you in advance Chris Cambridge, UK -- |
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Bob Koller
The first thing, always, is to check the power supply for voltage and ripple, and repair as required. But, the symptom you describe does sound like a failed U800, or, less likely, one of the horizontal deflection plate leads came off the CRT pin. Good Luck! From: cmjones012003 To: TekScopes@... Sent: Thursday, January 17, 2013 1:16 AM Subject: [TekScopes] 2465 - impending U800 failure?
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Hello all,
I haven't posted to this list in a long time but have just been lurking, I'm afraid. One of my trusty 2465s has started to give trouble. It's serial number 102481. I bought it used, surplus about 10 years ago and it's had plenty of hard use since, being my daily workshop scope. I've never even undone the case screws - it's Just Worked, and stayed spot-on accurate. I think the tube is a bit tired, since the trace loses focus at high brightness and it's impossible to get the whole screen (corners and centre) exactly in focus at the same time, though it's always been like that and it's good enough. Yesterday, I switched it on to use it, and it came up as usual but after a couple of minutes the entire display, readouts and all, suddenly jumped off the right hand side of the screen and stayed there. I could just about see the left hand end of the trace by winding the horizontal position all the way over to the left, and the scope was clearly still working otherwise: the bit of trace I could see responded to input signals and adjustments of the controls. I noticed also that pressing the 'beam find' button put the display back in the centre, but shrunken as I'd expect. I tried the scope again a little later on and the display came back, but tried it again today and it worked for a few minutes then suddenly jumped off to the right again. I do have the service manual for it, but before I start digging in, are these the typical symptoms of U800 failure? Searching the group, it seems that U800 failure tends to push the display to the left, and I haven't seen anyone document how 'beam find' behaves in that case. Thank you in advance Chris Cambridge, UK -- http://www.martin-jones.com/ |
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On 1/17/2013 1:16 AM, cmjones012003 wrote:
I tried the scope again a little later on and the display came back, but tried it again today and it worked for a few minutes then suddenly jumped off to the right again.Chris, I don't know how typical, but this is exactly what mine did having I bought it "working" at our local swap meet. I would not say impending, I think it has happened. Eventually I replaced the U800 with one found in a "parts unit" bought on eBay for $125 and all has been fine since. Obviously this required a bit of risk taking. Sources for the horizontal hybrid are few and far between, and I didn't like the alternatives. My "parts unit" has provided a few other things that have come in handy, a spare tube, fan and HV module among others. In the end, I did a complete overhaul, loads of new caps, new battery, and a full calibration, so I'm hoping it will see me out. Yours at least will probably also need a new memory battery if you've had it that long. Dan |
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--- In TekScopes@..., "cmjones012003" wrote:
I could just about see the left hand end of the trace by winding the horizontal position all the way over to the left, and the scope was clearly still working otherwise: the bit of trace I could see responded to input signals and adjustments of the controls. I noticed also that pressing the 'beam find' button put the display back in the centre, but shrunken as I'd expect. Mine did exactly the same - and the effect of the beam finder was similar too. I bought a replacement from a helpful man in California (Ebay seller "2465b"). He advised me that the original IC was mounted with two lock washers between the package and the board. This is a BAD IDEA as it creates an air gap and prevents any cooling that may be had from contact with the board - bolt the replacement directly to the board surface. A little heatsink compound seems to help as well. I also reamed out some of the case cooling holes directly beneath the position of U800 to improve the incoming airflow. There's usually several second-hand U800s on Ebay - but avoid the ones made by Maxim. Not as reliable as the original Tektronix ICs, I understand. John G4FDD |
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2465b helpful? My a*s!
This Russian immigrant is a cheat and charlatan - search back on the forum - and you will see where he has sold perhaps hundreds of 2465-series scopes which were "modified" by him. He cut and mutilated the 2445-series PCB's (unauthorized by Tek), and played games with the filter circuits to make them appear like 2465-series motherboards. He then inserted them into defective 2465-series cases, and represented and sold them as 2465-series scopes. He admitted to doing this, expressed no regret, and was quite arrogant about it. A number of people on this forum were scammed by him. He manages to survive, because he is a slick marketer, as are most charlatans. He outclasses the worst of the Chinese counterfeiters and cheats, and thst's no compliment at all. Avoid him at all costs. |
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I have a working 2232 that I suspect may have originally been a 2224
which is the uncommon 60 MHz version. Besides some cosmetic discrepancies, the fastest analog sweep speeds have an awful lot of horizontal displacement although that may be a calibration issue. Once my other 2232 is up and running, I will do a careful comparison between them. I do not have any data on the 2224 to use but it may be possible to tell by checking the vertical response temperature compensation networks which are different between the 100 MHz and 60 MHz oscilloscopes which use the same hardware. On Sun, 20 Jan 2013 06:21:59 -0000, "dehav7" <yachadm@...> wrote: 2465b helpful? My a*s! |
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Tom Jobe
¿ªÔÆÌåÓýHi David,
The 2224 conversion to a 2232 has come up before on this
group.
Denis Cobley provided lots of information about this issue
years ago, and Jack Rouse discovered that it came down to
the?presence of jumper W3400 on the storage board to turn?a 2224 into
a 2232.
The 2224 has W3400 removed, the 2232 has W3400 installed (the
jumper is just a piece of wire).
It was believed that the firmware was the same for the 2221A,
2224 and 2232, and that the firmware chip determined which scope?it was
installed in by the presence/absence of?some?jumpers. Someone studied
the ROM image and said that this all seemed to be true.
Also, you needed to cut the thin plastic face overlay to
expose the additional switches?across the top, just to the right of the
CRT.
A pointed hobby knife and some extra square buttons from
another 222x was all it took.
I did one or two of these 2224 to 2232 conversions using this
information and?everything seemed to work perfectly.
Jumper W3401 is on the A10 board and is shown at location 3A
on the 2232 schematic number <15> titled "Digital Acquisition and
Memory".
Physically W3401 is located at 2F on the A10 board
layout.
You might?consider checking that your 2224/2232 has W3401
installed before you do your bandwidth testing.
tom jobe...
PS Every time I go through the Tekscopes message archive, I
marvel at all of the fine posts put up by Denis Cobley. There must be a thousand
of them and they are all informative. I sure wish Denis was back on
Tekscopes.
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Sounds very much like the U800 issue.
About six months ago a posted about baking some U800s that had failed this way and was able to rejuvenate them. I put one of the U800s in a test scope and it's still working to this day. I'm amazed. --Victor --- In TekScopes@..., "cmjones012003" wrote: [SNIP]
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I sold an apparently working U800 to a list member from an old 2445. Though the scope seemed to function just fine on initial testing, he later emailed this back:
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"I left FB after doing just a quick test at 1ms/Div. After more testing I discovered that it is very noisy at 10X when time base is faster than 5ns/Div after a quick 2 minute warmup. This Horz Amp is not usable." So I refunded his money. What I take this to mean is that the U800 can be failing or not meeting specs even without total failure. Just something to keep in mind. Chip --- In TekScopes@..., "victor_j_silva" wrote:
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Hi Chip,
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That was me! I do remember because you were very nice with the refund even though I had left Pos FB already. Not many would do that. I have seen three main failure modes on U800: 1. The trace shifts to the left (operator's left when looking at the CRT) as the scope warms up, usually 5 to 10 minutes. These are the ones I baked and revived! 2. The chip is very noisy, by this I mean there is a lot of jitter on a very fast step response so that on every retrace the horizontal position of the rising waveform will vary by 500ps to 1ns. Unlike a good U800 which will show the retrace at the same position. 3. Outright dead. The U800 you sold me was failure #2 type. --Victor --- In TekScopes@..., "random.path" wrote:
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Is all of this heat related? One of the first things I did when getting my 2465BDM was strap a very large heat sink to the U800 chip with good quality thermal compound and very secure mounting. It's larger then the chip. It runs just over room temperature with the case on. I measured it with a type K probe through the vents and touching the middle of the heat sink with a dab of thermal compound over a half hour or so time frame.
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I do notice mine drifts a tiny tiny bit on warm up, one or two mm to the left. It later snaps back about 1mm to the right. Jeff On 1/20/2013 2:00 PM, victor_j_silva wrote:
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Doubtful it's heat related. The chip runs at ~117F with no heatsink, that's pretty low.
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Search for U800 you'll find hundreds if not a thousand posts on the subject. Be careful with how large a heatsink you attach to the studs. A little bang on the bottom of the scope and you'll short out the -5V supply. --Victor --- In TekScopes@..., Jeff Machesky wrote:
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Thanks Victor, the heat sink is actually electrically isolated. It also has just enough clearance that you would really have to do some damage to the scope in order to get it to impact. Good piece of advice none the less.
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Jeff On 1/20/2013 3:45 PM, victor_j_silva wrote:
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Dave C
Last time 'round on this topic I designed a heatsink that contacts only the metal tab parts of U800, not the plastic body. This is the intended (I think) means of getting the heat out of the chip.
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The drawing of this heatsink is in the Tekscopes files page on the Yahoo Groups web site. Look for a folder titled "U800". Its in there. Dave -=-=-=- On 20 January 2013, at 2:05 PM, Jeff Machesky wrote:
Is all of this heat related? One of the first things I did when getting |
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Removing the heat from the plastic should in turn drop the temperature of the metal fin some. Now does that produce undesirable thermal shifts, no idea. In my case I'm pulling heat from a little of both, but mostly the plastic.
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So what does baking the chip actually fix? I know some IC's are sensitive to humidity, but this is usually only just before the high temperature of a reflow oven. The trapped moisture can cause defects when heated. Jeff On 1/20/2013 6:07 PM, Dave C wrote:
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It may fix some of the U800s that have failed:
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Please search this forum: "U800 baking" This has been discussed ad nauseam. --Victor --- In TekScopes@..., Jeff Machesky wrote:
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Thanks Victor, interesting thread. If it is humidity based then I'm glad I live in Arizona. Seams like leaving them for a long time packed in silica gel might also help. Interesting in any event.
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Jeff On 1/20/2013 6:37 PM, victor_j_silva wrote:
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On 18/01/2013 00:45, livingj2 wrote:
--- In TekScopes@... <mailto:TekScopes%40yahoogroups.com>,Further to this, I've now had chance to look inside the offending scope. In the fault condition, one of the outputs of U800 wanders up to about 60V and nothing else seems to change. Power supplies are all present, correct and clean. Cooling the chip makes the display drift back towards the centre, so I think it's the culprit. Interestingly, the chip is a Maxim one with a 1995 date code, and it shows signs of having been replaced before, given that all the other date coded chips in the scope are 1983. I'll start looking for a replacement, or maybe try the baking technique since I have nothing to lose... Chris |
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Hi John,
I have really been wondering about those star washers myself. They seem to defeat the purpose of the foil on the PCB considerably. I am working on a U800 failure now and have some concerns about removing them. #1 maybe they are there to keep the board from long term heat damage. #2 maybe with the air flow coming directly through the cabinet holes some goes under the IC. If anyone really knows anything about this I would greatly appreiate a reply. In regard to purchasing any hybrids from eBay be very carefull they are not refurbished. There is one or two places in Asia that bakes these hybrids to re-stick the wire bonds. U800 was the first IC I am aware of this being done. Later the channel switch and others were done. Sphere BC offers this service and they are honest that it may only be a short term fix. Also it does not always fix the IC. Personally I have not used them and hope I never need to. Respectfully, Dan Shores --- In TekScopes@..., "livingj2" wrote: horizontal position all the way over to the left, and the scope was clearly still working otherwise: the bit of trace I could see responded to input signals and adjustments of the controls. I noticed also that pressing the 'beam find' button put the display back in the centre, but shrunken as I'd expect. but tried it again today and it worked for a few minutes then suddenly jumped off to the right again. are these the typical symptoms of U800 failure? Searching the group, it seems that U800 failure tends to push the display to the left, and I haven't seen anyone document how 'beam find' behaves in that case. Mine did exactly the same - and the effect of the beam finder wassimilar too. I bought a replacement from a helpful man in California (Ebay seller "2465b"). He advised me that the original IC was mounted with two lock washers between the package and the board. This is a BAD IDEA as it creates an air gap and prevents any cooling that may be had from contact with the board - bolt the replacement directly to the board surface. A little heatsink compound seems to help as well. I also reamed out some of the case cooling holes directly beneath the position of U800 to improve the incoming airflow. made by Maxim. Not as reliable as the original Tektronix ICs, I understand.
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Chris
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Beam Find will center and shrink the display. The display may look fairly well centered with the U800 failure. What you describe souns like a U800 failure, however at least check your power supplies first. Also make sure one of your horizontal CRT wires are not loose. Good luck, Dan --- In TekScopes@..., "cmjones012003" <chris@...> wrote:
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David Hess
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