I use acetic acid (vinegar) to clean alkaline battery residue and baking soda in solution to clean acid battery residue.
I have a wash bottle of both on the work bench.
I follow this up by flooding the area with distilled water with the board angled such that the contaminated area is closest to the bottom.
This is followed by cleaning the area with IPA then warming with a hot air gun.
Ensure that you neutralize any residue that has made its way into vias.
If the board is multi layer and the residue has gotten into the inner layers, the board may take heroic efforts to salvage it.
Glenn
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Show quoted text
On 8/5/2018 2:45 PM, Richard L. Wurdack wrote:
Did someone here suggest Ammonia (Ammonium Hydroxide solution, Washing Ammonia) as a way of removing the crud from failed alkaline battery corrosion?
Dick
--
-----------------------------------------------------------------------
Glenn Little ARRL Technical Specialist QCWA LM 28417
Amateur Callsign: WB4UIV wb4uiv@... AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"
|
Did someone here suggest Ammonia (Ammonium Hydroxide solution, Washing Ammonia) as a way of removing the crud from failed alkaline battery corrosion?
Dick
|
Hi Roy, As odd as it might sound, the 2215 is very unlike the 2215A (in many ways) and what is known about adding a simple cooling fan does not apply to the 2213 and 2215 as well as many of the other small 22xx scopes that were made around the world. Even common scopes like the 2213A do not have this undocumented fan circuitry on the mainboard. The common 22xx scopes this fan modification applies to are the 2215A, 2235 and the Military version of the 2235, the AN/USM-488 and probably the 2235A as well. The component numbers are printed on the mainboard of the 2215A and the 2235, but the markings are gone on the military version even though the unused fan circuitry is there. Higher models such as 2236, 2230, 2232, 2221 come with a fan and a fan circuit that is similar. Some are half wave like the 2236, others are full wave like the 2232. Of the ones I have seen, they all use pin 20 on the main transformer, and also use pin 22 if it is a full wave supply on that particular model. Below is a document from 2008 that explains the fan circuit and components I used, and includes some of the good input I got from other Tekscope members back then. (Unfortunately the photo album capability on this group will not allow posting this related document with the photos because it is not an 'image' file) tom jobe... PS I have installed the fan circuit on quite a few 22xx scopes in the last 10 years, and the uF value of the capacitor does not seem to matter much, nor does going to a full wave supply make much difference in the end result. Adding another diode over to pin 22 of the transformer, on the bottom side of the mainboard is all you need to get a full wave supply if you want to try it, and a photo of that will also be added to Leo's photo album after I edit the file names to help explain what is in each photo. I see someone else has posted some photos on this same subject to Leo's album but with no hint of what you are seeing in the file names. Components I have used include: CR965 = ultra fast diode, one amp R965 = 3 ohm resistor, 1/4 Watt C965 = 100uF to 1000uF capacitor Recently the question was asked "was there an optional fan for the AN/USM-488 oscilloscope (the military version of the 2235)? and some off line discussion led to some interesting findings that a few of you might like to hear about. There was no optional fan as far as anyone seems to know, but there are some unused traces and solder pads on the mainboards of the 2215A, 2235, and USM-488 (and other similar 22XX's), that appear to have been made for a power source to run such a fan. On the 2215A and 2235 I was looking at, the component numbers were silk screened on the mainboard in these empty locations, and these component numbers are not in the electrical parts listings or shown on the schematics I looked at. The USM-488 does not have the markings on the mainboard, but all of the same traces and solder pads are there. Looking at the front of the oscilloscope, these component locations are near the right edge of the mainboard, just in front of the aluminum plate that is the heat sink for the two inverter transistors and the one MOSFET of the inverter. It is a half wave supply coming from pin 20 (the 8.6 volt winding) of the main transformer to the cathode of diode CR965. The anode of CR965 connects to the resistor R965 which becomes the minus pin of the 2 pins called P9965 (which is where the fan plugs in). The positive pin of P9965 is connected to ground and a capacitor C965 goes between the plus and minus pins of P9965 to smooth the half wave power. (the fan's positive supply is ground, and the fan's negative supply comes from this negative supply circuitry) I did not know what to do for component values so I studied the full wave supply for the 2232 fan and my electronic text books for awhile, and came up with these values. CR965 is a one amp diode, R965 is a 3 Ohm resistor, and C965 is a 1000 uF capacitor. The resistor limits the current to protect the diode at start up, and the capacitor was probably intended to be fairly large as the capacitor mounting holes are on 0.3" centers (7.6 mm). The capacitor for the 2232 full wave fan supply is a 4700 uF, so 1000 uF seemed like a reasonable place to start, and it physically fit in there nicely. The fan is a 60 mm / 12 volt computer style fan, and it fastens to the inside of the back of the metal case where the air holes and the square 50 mm hole pattern is. All of the 60 mm fans seem to have the 50 mm bolt pattern, and I happened to find one fan that had threaded inserts in the four holes so no nuts were even required. The fan is on the inside of the case blowing the air outwards just like your computer does. I did this fan experiment on a 2215A I have been working on for some time. With this modified oscilloscope running, the fan is getting about -8.4 volts, which keeps it fairly quiet yet it does move some air, and there is about 60 mV of ripple at the fan connection. Next I thought I would try making this a full wave fan supply, so I added another identical diode and a piece of wire (all in shrink tubing), to the back of the mainboard. This second diode's cathode connected to pin 22 of the main transformer (the other end of the 8.6 volt winding) and went over to the end of resistor R965 where the first diode CR965 connects. The full wave arrangement delivers about -8.6 volts (up from -8.4) and the same 60 mV ripple so it seemed foolish to bother with the full wave configuration and I removed it. In one of my books it talked about how you need about 0.5 volts of ripple in the first stage of a power supply to make sure both diodes are actually working, and I only had 60 mV. tom jobe ¡. tom jobe wote Hello John, Your mathematical explanation helps makes more sense of this for me. This morning I was reading in one of my older text books about all of this, and they gave a rough formula to figure out the approximate capacitor required for a given ripple on a half wave rectified 60 Hz sine wave circuit. C = It/V where "C" is the capacitor size in Farads, "I" is the load in amps, "t" is the time in seconds, and "V" is the allowed ripple in volts. If you plug in .12 for the fan load in amps, times .000050 for the 50 uS period of 20 kHz, and divide by .05 for 50 mV of ripple, it shows you that you only need 120 uF The square wave would have a higher RMS value than the sine wave, so I guess the capacitor could probably be even less, maybe only 100 uF?... if I haven't messed this calculation up somewhere! If there is no real downside to leaving the 1000 uF capacitor in there? I think I will just leave it alone, and move on. I've had a good time with this project, and I thank you for your help! tom jobe... tom jobe wrote: Hello John,
Thank you for the additional insight into the capacitor sizing. I'm in
way over my head, so I can use all of the help I can get to understand this!
One thing I failed to mention was that this transformer runs at 20 kHz,
and the winding you are connecting the fan to is an approximately 19 volt
Peak to peak square wave with a period of 50 uS. (this square wave meters 18.4 VAC with an RMS DVM)
OK. The same formula applies, but the dT is 25 or 50 uS. With a square, the cap will be oversized. The square wave is fairly symmetrical, and when it was being rectified
full wave, the resulting trace (without a capacitor) was not a perfect straight line of course, but it wasn't bad. The full wave rectified square wave trace is made up of approximately straight pieces on the tops and bottoms of the square waves with little glitches in-between every 25 uS, so the smoothing probably does not require nearly as much capacitor as a full wave rectified sine wave, or half wave rectified square wave would. Correct. I was surprised at how the ripple did not change much when the fan
Supply was changed back to half wave rectification, but I guess the fan uses so little power (0.12 amp?) that the capacitor does not get pulled down very much in the 25 uS between half wave pulses. The ripple depends on the load current and the cap size. With a square wave, current is supplied throughout the cycle, hence the lower ripple. Arthur pointed out in another reply to this subject, that 1000 uF is
probably far too much capacitor for this little fan supply. What made me
start with 1000 uF was two things, one was that a study of the similar
full wave fan supply in a 2232 has 4700 uF (was Tektronix trying to tell me
something?), and the other thing was the mounting holes for the
capacitor were on 0.3 inch centers so the smaller capacitors would not sit down on
the board properly because their lead centers are closer together at 0.2
inch or less. Also. I could not see that it would hurt anything to have a larger
capacitor if the current was limited through the diode at start up, even
though I am questioning my choice of resistor size at just 3 ohm. (the
2232 uses 2.7 ohms of resistance with a 4700 uF capacitor)
tom jobe....
The charging current is roughly 1/2 x 19 = 9.5 V peak. The resistor is 3 ohms, so the current is limited to about 3 amps. I = C dV/dT, soI/C = dV/dTso3 / 0.0047 = 14,100V/sec = 0.014 V/uS so in 25 uS (1/2 period)it rises 25 x 0.014 = 0.35 V that's about 1V in 3 cycles or 10 V in 30 cycles, which seems reasonable. Best, -John
PS I'm not trying to design anything here, I'm just trying to learn the
basics with small projects like this, and I thank all of you for helping
me.
----- Original Message -----
From: "J Forster" <jfor@...>
To: <TekScopes2@...>
Sent: Saturday, February 02, 2008 7:18 PM
Subject: Re: [TekScopes2] Optional fan for the 2235 or USM-488?
[snip]In one of my books it talked about how you need about .5
volts of ripple in the first stage of a power supply to make sure both diodes
are actually working, and I only had 60 mV.
It is good fun learning about electronics with this fine Tektronix
gear!
tom jobe...
No. If you look at the waveform to a capacitor input filter on a 60 Hz
line, you should see an increased voltage bump every 1/120th of a
second. If you see one every 1/60th of a second, it's a half wave rectification.
The amplitude depends on the C size and load current:
I = CdV/dTso dV = I / C dT
dV is roughly the P-P voltage of the ripple
dT is the interval between charging pulses(1/60 or 1/120 second)
SO:
dVincreases w/ current drawand decreases w/ capacitor size.
Best,
-John
Hello Arthur, Yes, the diodes I used came from a junk 2235 mainboard, and they were rectifier diodes from one of the secondary supplies. I checked them on the curve tracer and they seemed to be identical. You are right about getting almost peak voltage across the large 1000 uF cap. Thanks for your help! tom jobe... On 8/4/2018 7:47 PM, Roy Morgan wrote: Tom,
I would want to do this fan modification to my 2215. A modest amount of cooling can help electronics life span a lot.
So I¡¯d be most grateful for the pictures you have.
Thanks in advance.
Roy Morgan
k1lky68@... <mailto:k1lky68@...>
On Aug 4, 2018, at 8:08 PM, tom jobe <tomjobe@... <mailto:tomjobe@...>> wrote:
Hello,
Do not forget that scopes such as the 2215A and the 2235 have the fan drive circuitry you need already printed on the mainboard,...
I have some photos of the above modifications that I can send to anyone directly on request.
|
BTW...have a read on this snubbing guide, especially concerning contact bounce which exists no matter how 'crisp' the switch action is.
|
On Sun, Aug 5, 2018 at 11:50 AM, Vincent Trouilliez wrote:
On Sun, Aug 5, 2018 at 12:38 AM, satbeginner wrote:
I had a quick look on the 2232 schematics
The 2232 has a full wave rectifier (CR965 & CR967 coming from pin 20 and 22 of the transformer)
That's true for the early units, which drive the fan at 8.6V via the a middle
tap and the two +/- 8.6 rails.
But I see there was a different wiring for later 2232's : this time it's
running at a slightly higher voltage : 10V. It's across the +/- 5V rails and
doesn't use the middle tap/ground, hence a 4 diode bridge.
I don't know why they changed the wiring. Either they felt they needed a bit
more voltage and/or they decided that running a noise factory such as a fan,
from the 8.6V rails that power the sensitive analog stuff, was far from ideal,
even though the fan is wired upstream of the LC filtering networks.
and a capacitor C965 and a current limiting resistor R965 installed to power the additional fan.
At least this bit is common to both designs...
Based on the empty room on my 2215A PCB it looks like they only planned a half
wave rectifier?
There is room for 1 diode coming from pin 20 of the transformer, 1 capacitor
and 1 resistor and a 2-pin connector for the fan. OK ! So yet another wiring arrangement ! LOL
So in short... in all cases they put that 2.7ohm resistor in series, and that
big 4700uF cap across the fan... but as far as voltage source goes, you pretty
much tap the secondaries in any way that you see fit, so long as you tap
straight from the transformer pins so that the crap/electrical noise from the
fan can still be filtered downstream by the LC PI networks, and keep the
delicate analog stuff of the scope happy.
Well that's how I understand it so far...
Will try this, Yes, keep us posted, and take some waveforms and measurements to see how this
crude single wave rectification performs... and of course measure ripple
before/after the mod, to make sure it's still within specs ^^
Regards,
Vincent Trouilliez
Un saludo,
Leo
Hi Vincent, I took some pictures of the empty spaces on my PCB and how I filled them with the three components and the connector. The pictures and the additional schematics are added to my album /g/TekScopes/album?id=64919For now I cannot measure any (extra) ripple because I do not have the fan yet.. :-) To be continued, Leo
|
On Sun, Aug 5, 2018 at 12:38 AM, satbeginner wrote: I had a quick look on the 2232 schematics
The 2232 has a full wave rectifier (CR965 & CR967 coming from pin 20 and 22 of the transformer) That's true for the early units, which drive the fan at 8.6V via the a middle tap and the two +/- 8.6 rails. But I see there was a different wiring for later 2232's : this time it's running at a slightly higher voltage : 10V. It's across the +/- 5V rails and doesn't use the middle tap/ground, hence a 4 diode bridge. I don't know why they changed the wiring. Either they felt they needed a bit more voltage and/or they decided that running a noise factory such as a fan, from the 8.6V rails that power the sensitive analog stuff, was far from ideal, even though the fan is wired upstream of the LC filtering networks. and a capacitor C965 and a current limiting resistor R965 installed to power the additional fan. At least this bit is common to both designs... Based on the empty room on my 2215A PCB it looks like they only planned a half
wave rectifier?
There is room for 1 diode coming from pin 20 of the transformer, 1 capacitor
and 1 resistor and a 2-pin connector for the fan. OK ! So yet another wiring arrangement ! LOL So in short... in all cases they put that 2.7ohm resistor in series, and that big 4700uF cap across the fan... but as far as voltage source goes, you pretty much tap the secondaries in any way that you see fit, so long as you tap straight from the transformer pins so that the crap/electrical noise from the fan can still be filtered downstream by the LC PI networks, and keep the delicate analog stuff of the scope happy. Well that's how I understand it so far... Will try this, Yes, keep us posted, and take some waveforms and measurements to see how this crude single wave rectification performs... and of course measure ripple before/after the mod, to make sure it's still within specs ^^ Regards, Vincent Trouilliez
Un saludo,
Leo
|
On Sat, Aug 4, 2018 at 07:56 PM, Roy Morgan wrote: Vincent,
This is certainly a mod I want to do to my 2215. A modest amount of air improves the life of electronics a lot.
I¡¯d be grateful to get the pictures you have, with my thanks.
Roy Morgan Hi Roy, It was Tom Jobe (which you quoted) who offered this info, not me ;-P I am interested in it too ! :-) As for posting Photos, I think it's much better to put them in a clearly/explicitly named, dedicated album, because of it is of general interest for sure. Vincent Trouilliez
|
Hello,
I had a quick look on the 2232 schematics and my 2215A board layout:
The 2232 has a full wave rectifier (CR965 & CR967 coming from pin 20 and 22 of the transformer) and a capacitor C965 and a current limiting resistor R965 installed to power the additional fan.
Based on the empty room on my 2215A PCB it looks like they only planned a half wave rectifier?
There is room for 1 diode coming from pin 20 of the transformer, 1 capacitor and 1 resistor and a 2-pin connector for the fan.
Will try this,
Un saludo,
Leo
|
Hi, I for sure want to add a fan too! The album I made is open for the group, so you can simply add the pictures here: /g/TekScopes/album?id=64919Un saludo, Leo
|
Tom,
I recommend posting on groups.io
George
BTW, you owe me a lunch time visit...
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Show quoted text
On Aug 4, 2018, at 5:08 PM, tom jobe <tomjobe@...> wrote:
Hello,
Do not forget that scopes such as the 2215A and the 2235 have the fan drive circuitry you need already printed on the mainboard, but it is un-documented in the service manual.
You just populate the half wave fan circuit with a few components, and put a 60mm 12 volt fan on the back panel, on the two fan mounting holes that are already there.
This Tektronix fan circuitry drives the fan at a much reduced voltage, so noise is not a problem.
About those large resistors under the CRT that often scorch the mainboard... on the later production 22xx scopes Tektronix raised those resistor up so air could get in underneath them.
You can easily raise your your existing resistors by removing them and attaching some simple extensions to the resistor's leads. Do check the value of your existing resistors to make sure they have not been cooked too much and had the value changed before you raise them. Also consider raising them at alternating heights so you don't make a "wall" of side by side resistors that is just up higher.
My guess is that the burnt mainboards are in scopes that were run 24/7 and had the scope installed in a level position, so there was no 'chimney' effect to make the heat rise through the scope.
I have some photos of the above modifications that I can send to anyone directly on request. If you want these photos to be posted elsewhere, you can do it.
tom jobe...
On 8/4/2018 6:58 AM, Vincent Trouilliez wrote:
No idea about FET temperature, as I have no way to measure temperatures yet ! A thermocouple for my DMM and a simple IR "gun" are on my list of things to buy, but the thing is sooooo long, no idea when I will get round to it ! ;-)
As for discoloration/overheating, I don't see any sign of it on my scope, anywhere. All power resistors look sparkling new and so does the PCB in their vicinity. I guess that only means my scope happens to be a low hour unit.
These beefy resistors overheating in the 2215 and 2215A ans 2235 scopes, as per your findings, is probably due to the fact that these 3 scopes are among the few 22XX scopes which did not have a cooling fan.... what a "coincidence" ! ...
Well I can only speak for my personal 2215, which definitely does not have a fan. However I just downloaded the service manual of both the 2215A and 2235 to have a quick look at their mechanical parts list, and they indeed do not seem to have a cooling fan. All these 3 scopes being so closely related technically (the 2215 being an updated 2215 AIUI, and the 2235 just being a 2215 with improved B/W), I guess it's consistent.
Probably why some people advise to add a cooling fan, especially since the back of the cabinet/chassis already provides the "grill" where a cooling fan would go. So it's not that big of a job as far as mechanical integration goes, at least.
All that being said, unless your scope is not working properly (other than SMPS issues I mean), then I don't see any emergency to replace those resistors. Unless of course your aim is to spend time and money to make the scope as good as it can get, and as reliable in the long term as can be.
If so then yes, I guess adding a cooling fan and replacing those resistors wouldn't hurt. While doing so, you could fit higher wattage resistor (a size up), since space is not at a premium in this area of the scope, from what I can see on my 2215. Also you could try and raise the resistor off the board by half an inch or so, to improve cooling a bit and keep them from burning the PCB any further.
I remember a discussion on here not so long ago, about dedicated tools used to form the leads of (these very ?) power resistors to raise them from the PCB.
Don't ask me to dig out that thread though...my searching skills are not that good... but it's there... somewhere...
I remember it because I found it cool to have a nice little tool to be able to form the leads "cleanly", in a professional looking manner. Will definitely get one of these tools some day...
As for my 2232, was involved indeed, especially since it was my first "meaty" repair experience (definitely more than just replacing a blow fuse I mean ! LOL) , and had zero working knowledge of the 22XX scopes not even SMPS in general...
Still, I need to get back to that scope, to recap the PSU, as well as try to get rid of the SMPS annoying whine issue, and another issue also, where the trace on the CRT look "dotted" at some sweep speeds. Never a dull moment with this old 2232 ! ^^ But that will be for later...
Regards,
Vincent Trouilliez
|
Vincent,
This is certainly a mod I want to do to my 2215. A modest amount of air improves the life of electronics a lot.
I¡¯d be grateful to get the pictures you have, with my thanks.
Roy Morgan
k1lky68@... <mailto:k1lky68@...>
toggle quoted message
Show quoted text
On Aug 4, 2018, at 8:08 PM, tom jobe <tomjobe@... <mailto:tomjobe@...>> wrote:
Hello,
Do not forget that scopes such as the 2215A and the 2235 have the fan drive circuitry you need already printed on the mainboard, but it is un-documented in the service manual¡.put a 60mm 12 volt fan on the back panel, on the two fan mounting holes that are already there. I have some photos of the above modifications
|
As an aside....i had to snub a massive desulfator pulse of about 600A that delivered significant back emf from cable and battery inductance.
I was unable to quantify it until I placed a pulse diode good to 2KA and feed a 2200uF cap and measure the Cap voltage rise over time.
Eventually had to place an automotive lamp of 25W to dissipate the energy.....worked well....lamp hits just north of 13V.
I improved the design recently with a redundant lamp.
|
Hi Fabio I sent the picts in an email to you PM but comcast has changed there email to a new system so I'm not sure if you got it or not.
Jim
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Show quoted text
On August 3, 2018 at 12:23 PM Fabio Trevisan <fabio.tr3visan@...> wrote:
Hi Jim,
Feel free to send me the pictures (PM to fabio.tr3visan@...).
I will be glad to post it to the photos area of Tekscopes.io, and reply to you with a link to the folder.
Rgrds,
Fabio
On Fri, Aug 3, 2018 at 03:07 PM, Jim Olson wrote:
Fabio I have the pictures but I'm not using any kind of photo posting service
it's gotten to complicated and I don't post much to forums anyway so can I
send them to you and you can post them up?
Jim
On August 3, 2018 at 7:26 AM Fabio Trevisan <fabio.tr3visan@...> wrote:
Hello Jim,
I owed and restored a 464 with DM44 (now given to a friend) and I don't
think there are any other "optional" boards linked to the presence (or
absence) of the DM44.
The only optional boards that apply to the 464 / 466 are:
A. The optional DC inverter board (option 7)... That one can't co-exist with the DM44 (the inverter uses the same windings on the main transformer that are
used to power the DM44).
B. The composite video Sync Separator (Option 5), which bears some relation to the A5 sync board and could explain some changes.
I did hear once, from someone of this group, there was two versions of the
A5 Sync board... one that used the Tunnel Diodes, and another one which used a
Custom Tek IC to discriminate the trigger edge.
I`m not sure, but maybe this is what the -01 means...
I've never landed my eyes, however, on a schematic of the latter, or a later manual that included both.
But regardless of this board versioning, It seems rather odd to me that the
connections to the J6 are disconnected, and more so, that there is no
connection between the top and bottom side THROGUHOUT the board...
Moreover, there's nothing about the DM44 vs power to the A5 Trigger board... The DM44 takes its power from its own power supply and it's neither fed by the
A5 board, nor the A5 board feeds it.
Yet, the only reason I can think of for the through hole plating is missing throughout the board is, either a mass murderer technician stripped them off
by careless unsoldering, or yet, that it's a prototype board...
If it's the latter case, it could explain many things...
Maybe you can take a picture, post somewhere and link it here.
KRgrds,
Fabio
On Thu, Aug 2, 2018 at 11:40 PM, Jim Olson wrote:
I have a question about the A5 trigger generator sweep logic board
differences. I have two 466's with out the DM44 with the same trigger
board
670-3324-00 boards. I have a 464 with a DM44 with the 670-3324-01 board
and it
is vastly different from the 466 boards. All the DC voltage traces from
J-6
are disconnected all the through holes are unsoldered so there is no
interconnection from top to bottom through out the board. There appears to
be
no cable connection to the board from the DM44 to supply these?
The DM44 manual parts list's don't show that part number used for the
464/466
with the DM44 it shows the later 466 board and I can not find the optional
boards listed in the service manuals listed in the DM44 one.
The installation sheets for installing the DM44's don't list different or
optional boards used like the service manuals do?
So whats up with this bunch of missing info here!
Jim O
|
Hello,
Do not forget that scopes such as the 2215A and the 2235 have the fan drive circuitry you need already printed on the mainboard, but it is un-documented in the service manual.
You just populate the half wave fan circuit with a few components, and put a 60mm 12 volt fan on the back panel, on the two fan mounting holes that are already there.
This Tektronix fan circuitry drives the fan at a much reduced voltage, so noise is not a problem.
About those large resistors under the CRT that often scorch the mainboard... on the later production 22xx scopes Tektronix raised those resistor up so air could get in underneath them.
You can easily raise your your existing resistors by removing them and attaching some simple extensions to the resistor's leads. Do check the value of your existing resistors to make sure they have not been cooked too much and had the value changed before you raise them. Also consider raising them at alternating heights so you don't make a "wall" of side by side resistors that is just up higher.
My guess is that the burnt mainboards are in scopes that were run 24/7 and had the scope installed in a level position, so there was no 'chimney' effect to make the heat rise through the scope.
I have some photos of the above modifications that I can send to anyone directly on request. If you want these photos to be posted elsewhere, you can do it.
tom jobe...
toggle quoted message
Show quoted text
On 8/4/2018 6:58 AM, Vincent Trouilliez wrote: No idea about FET temperature, as I have no way to measure temperatures yet ! A thermocouple for my DMM and a simple IR "gun" are on my list of things to buy, but the thing is sooooo long, no idea when I will get round to it ! ;-)
As for discoloration/overheating, I don't see any sign of it on my scope, anywhere. All power resistors look sparkling new and so does the PCB in their vicinity. I guess that only means my scope happens to be a low hour unit.
These beefy resistors overheating in the 2215 and 2215A ans 2235 scopes, as per your findings, is probably due to the fact that these 3 scopes are among the few 22XX scopes which did not have a cooling fan.... what a "coincidence" ! ...
Well I can only speak for my personal 2215, which definitely does not have a fan. However I just downloaded the service manual of both the 2215A and 2235 to have a quick look at their mechanical parts list, and they indeed do not seem to have a cooling fan. All these 3 scopes being so closely related technically (the 2215 being an updated 2215 AIUI, and the 2235 just being a 2215 with improved B/W), I guess it's consistent.
Probably why some people advise to add a cooling fan, especially since the back of the cabinet/chassis already provides the "grill" where a cooling fan would go. So it's not that big of a job as far as mechanical integration goes, at least.
All that being said, unless your scope is not working properly (other than SMPS issues I mean), then I don't see any emergency to replace those resistors. Unless of course your aim is to spend time and money to make the scope as good as it can get, and as reliable in the long term as can be.
If so then yes, I guess adding a cooling fan and replacing those resistors wouldn't hurt. While doing so, you could fit higher wattage resistor (a size up), since space is not at a premium in this area of the scope, from what I can see on my 2215. Also you could try and raise the resistor off the board by half an inch or so, to improve cooling a bit and keep them from burning the PCB any further.
I remember a discussion on here not so long ago, about dedicated tools used to form the leads of (these very ?) power resistors to raise them from the PCB.
Don't ask me to dig out that thread though...my searching skills are not that good... but it's there... somewhere...
I remember it because I found it cool to have a nice little tool to be able to form the leads "cleanly", in a professional looking manner. Will definitely get one of these tools some day...
As for my 2232, was involved indeed, especially since it was my first "meaty" repair experience (definitely more than just replacing a blow fuse I mean ! LOL) , and had zero working knowledge of the 22XX scopes not even SMPS in general...
Still, I need to get back to that scope, to recap the PSU, as well as try to get rid of the SMPS annoying whine issue, and another issue also, where the trace on the CRT look "dotted" at some sweep speeds. Never a dull moment with this old 2232 ! ^^ But that will be for later...
Regards,
Vincent Trouilliez
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One more possibility for the failures in the 2465x scopes.? The inrush thermistors are effective only when they are cold.? Turning off and immediately back on means there will be inrush current.? The thermistors will still be hot from recent operation, yet the storage capacitors will be discharged from the last power down cycle.? I would not think this could be a significant problem but it does happen.
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On ?Saturday?, ?August? ?4?, ?2018? ?04?:?44?:?03? ?PM? ?CDT, M Yachad <yachadm@...> wrote:
Gentlemen
Thank you all so much.
I have learnt so much stuff about a subject about which I knew almost nothing.
Important points:
SMPS does not have inductive kick, therefore a capacitor across the on-off switch poles is not useful.
Inductive kick is present on Linear power supplies, and therefore an X-Y cap is useful across the switch poles.
The user should make snappy contact, without delays, when activating a push-push switch, and/or install a firmer spring.
Relay contacts should be examined to see if the circuit can benefit from two diodes resulting in 2x Vf, or diode + resistor.
Menahem
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Gentlemen
Thank you all so much.
I have learnt so much stuff about a subject about which I knew almost nothing.
Important points:
SMPS does not have inductive kick, therefore a capacitor across the on-off switch poles is not useful.
Inductive kick is present on Linear power supplies, and therefore an X-Y cap is useful across the switch poles.
The user should make snappy contact, without delays, when activating a push-push switch, and/or install a firmer spring.
Relay contacts should be examined to see if the circuit can benefit from two diodes resulting in 2x Vf, or diode + resistor.
Menahem
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On 8/4/2018 4:30 AM, satbeginner wrote: On Sat, Jul 28, 2018 at 08:18 PM, Bert Haskins wrote:
Ringing test To check transformers.
The transformer must be removed first.
To do this you apply a small!!! pulse across one winding and observe the
amount of ringing.
This will show a lot of ringing on a good transformer.
If you don't have a good function generator, one of the 74xx14 pulse
generator/buffers can be made to work.
Example of waveform:
And then short one of the other windings.
This should make a great! difference in the appearance of the pulsed trace.
You can also try wrapping one or more turns of wire around the core and
shorting them.
If this checks out OK, I would very carefully check all of the other
parts around T906.
This method does take some practice but it is a great tool to have.
-Bert Hi Bert, Vincent and others,
The ringing test made sense to me, its is relying on the fact a coil has an inductance, so a steep current change will cause voltage to shoot up. (snubber tread all over :-)
But as soon as one of the windings has a short, this will dampen the whole thing.
I did the test, and it looks as if my transformer is still OK!! :-)
So, while waiting for parts (the FET's & Diodes) I ordered, I started looking in my stack of -over the years- harvested PS boards to see if I could find some useable parts.
I found for the diode a HER105 (400V, 1A, 75ns, 1,3V) and for the FET a P9NK70ZFP (700V, 7,5A, and faster rise- and fall times, 17ns - 13ns, 1 - 1,2 Ohm RDSon)
Based on the 200ns rise- and fall times the switcher is using and I measured before they should be OK.
The good news: it's working again!
The bad news: the FET gets rather warm, temperature goes up to 68 degree Celsius, which should be OK, but I just don't like these temperatures that hi gh. (Higher ON-resistance?? )ty Remember, this same basic circuit used in the 2230/32 scopes where there is a much! higher load on the PS. The fet runs warm but not hot. The hot fet is most likely from slower turn on/off, been there, had that. This really! raises the operating temp. Sorry I can't remember the fet that I ended up using, but I did hand select it using a verity of test methods..
So I have decided to not leave these parts in, but replace them with the faster diode and lower On-resistance FET when they arrive.
I also removed the brown, plastic TO-220 cover, and put in a small heatsink on both sides.
The FET's I ordered are full plastic TO-220 housing, so I don't need extra insulation.
I also ordered a 70mm 12V fan that I will put in, much like it's bigger brother, to create some airflow.
I took some pictures of the working scope: /g/TekScopes/album?id=64919&p=pcreated,,,20,1,0,0
To be continued,
Un saludo,
Leo
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No idea about FET temperature, as I have no way to measure temperatures yet ! A thermocouple for my DMM and a simple IR "gun" are on my list of things to buy, but the thing is sooooo long, no idea when I will get round to it ! ;-)
As for discoloration/overheating, I don't see any sign of it on my scope, anywhere. All power resistors look sparkling new and so does the PCB in their vicinity. I guess that only means my scope happens to be a low hour unit.
These beefy resistors overheating in the 2215 and 2215A ans 2235 scopes, as per your findings, is probably due to the fact that these 3 scopes are among the few 22XX scopes which did not have a cooling fan.... what a "coincidence" ! ...
Well I can only speak for my personal 2215, which definitely does not have a fan. However I just downloaded the service manual of both the 2215A and 2235 to have a quick look at their mechanical parts list, and they indeed do not seem to have a cooling fan. All these 3 scopes being so closely related technically (the 2215 being an updated 2215 AIUI, and the 2235 just being a 2215 with improved B/W), I guess it's consistent.
Probably why some people advise to add a cooling fan, especially since the back of the cabinet/chassis already provides the "grill" where a cooling fan would go. So it's not that big of a job as far as mechanical integration goes, at least.
All that being said, unless your scope is not working properly (other than SMPS issues I mean), then I don't see any emergency to replace those resistors. Unless of course your aim is to spend time and money to make the scope as good as it can get, and as reliable in the long term as can be.
If so then yes, I guess adding a cooling fan and replacing those resistors wouldn't hurt. While doing so, you could fit higher wattage resistor (a size up), since space is not at a premium in this area of the scope, from what I can see on my 2215. Also you could try and raise the resistor off the board by half an inch or so, to improve cooling a bit and keep them from burning the PCB any further.
I remember a discussion on here not so long ago, about dedicated tools used to form the leads of (these very ?) power resistors to raise them from the PCB.
Don't ask me to dig out that thread though...my searching skills are not that good... but it's there... somewhere...
I remember it because I found it cool to have a nice little tool to be able to form the leads "cleanly", in a professional looking manner. Will definitely get one of these tools some day...
As for my 2232, was involved indeed, especially since it was my first "meaty" repair experience (definitely more than just replacing a blow fuse I mean ! LOL) , and had zero working knowledge of the 22XX scopes not even SMPS in general...
Still, I need to get back to that scope, to recap the PSU, as well as try to get rid of the SMPS annoying whine issue, and another issue also, where the trace on the CRT look "dotted" at some sweep speeds. Never a dull moment with this old 2232 ! ^^ But that will be for later...
Regards,
Vincent Trouilliez
|
Ed makes a good point on AC power push-push switches. When they become sluggish it is a problem. Replace them if possible. Cleaning with IPA may help but may just contaminate the PCB. One thing that has helped for me is to replace the front spring with a somewhat stronger spring to get the slide action response as originally present. The switch becomes stiffer but moves between positions fast. Spring replacement can usually be done without dismounting the switch.
Kevin
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Hi Vincent,
I will wait for the proper parts, but after the test of the transformer I wanted some confirmation I was on the right track.
Question: do you have an idea of the temperature of the FET in your scope?
According to the datasheet, the FET installed now should be able to work up to 120 degrees Celsius, but like I said, I don't want stuff to be (so) hot.
Talking about hot: there is some discolouration of the PCB of the area around R256 - R259 and R266 - R271 (Vertical deflection circuit) and the second area around R888 - R 891 (Intensity, Focus & Blanking) .
I will check these too.
Looking for pictures of other 22xx scopes show that it's mostly the 2215A and the 2235 that seem to have the exact same thing going on, like this one here:
Several pictures of eg. a 2213 do not show the discolouration.
BTW, I read your 2232 repair story, that was quite a lot more work than I had to go through with my 2215A!!
Thanks for that information,
Un saludo,
Leo
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Ancel
satbeginner
Vince
Glydeck