Date   

Re: Tek 2230, almost fixed but with a problem out of my competences

Albert Otten
 

I've just measured the resistance across C9410 (storage board) and got around
175ohm (low?) in both 1k and 4k mode
Seems fine. Take into account that R7506 goes to -8.6VL, not to GND. Better short -8.6VL to GND for such a measurement. Then you will read about 140R.
Albert


Re: 5440 PS transistor selection

Szabolcs Szigeti
 

Hi,

Be careful, the calibration instructions are dispersed in multiple places
in the manual, probably because the 5440 mainframe was originally a two
part unit, with the display and the mainframe section. To fully
calibrate, you'll need a special plugin, the 067-0680-00 calibration
fixture. So check all parts of the manual, not only the Adjustments section!

Indeed the plugins for the 5000 series can be used in the 5400 series, but
not the other way around. There are some 5000 series plugins with Readout
(no N in the model number), they will work in both, but obviously readout
will only be available in the 5440.

For the 5CT1N check there are two capacitors that in some units are under
rated and will cause a lot of interesting results and sometimes smoke. I
had to replace them in my unit, they were already blown when I got the
plugin. See: http://hakanh.com/dl/docs/hardtofind/CT1N.pdf

I actually very much like the 5440 scope, obviously no match for a 7000
series, but has a very nice large and sharp screen, and some fairly nice
plugins.

Szabolcs


Dave Peterson via groups.io <davidpinsf=yahoo.com@groups.io> ezt írta
(időpont: 2021. jún. 15., K, 16:52):

Thanks Harvey,

I did discover the plug-in incompatibility when I tried installing the
5440 plug-ins in the 5111A. Jeff Dutky pointed me to the pertinent section
of the Tek Wiki that describes this.

In that I also found that the 5111A plug-ins are "forward compatible" and
work in the 5440. I was a tad surprised to see the 5A26 from the 5111A gave
readouts on the 5440. While tuning up the 5440, on a lark, I used the 5A26
from the 5111A and the 5A48 from the 5440 to prove I could get four
channels showing at once with 5 readouts. The time base is a delayed 5B42,
but can't do "dual" A/B sweeps. (That'd be 8 sweeps! :P) But it did prove
the scope could do the 4 channels. FWIW. I don't have much experience with
these scopes, so I don't even know if a dual delayed sweep time base is
available or possible. I rather doubt it. So I don't think there's a
lower-right quadrant readout to be had. I digress. Readouts are a whole
other thread!

The calibration procedure in the 5440 manual is rather brief, but it does
include a HV voltage check, which was within spec. The 5A48 need some very
slight tweaking to bring CH1 & CH2 into agreement and get the step
attenuator adjustments spot on. Once it was tuned it did very well with
edge compensation and provides very nice sharp traces across the volts/div
range. Noise, of course, shows up below 5mV/div. But that's to be expected
(see my other posts about my large FM interference from local broadcast
tower).

The horizontal cal seems a bit deficient, and the time base should be
calibrated too. It also has some knob damage to the delayed time/div
portion that I'll need to fix. And some switch maintenance. It'll need to
be partially disassembled to get at them. These issues are minor and don't
appear to affect the horizontal performance. The timing accuracy and
stability are good.

Perhaps I need to check the 5CT1N supplies in the center slot of the 5440?
Could it be a supply issue in the curve tracer? The cal does have one
swapping the vertical plug-in back and forth between the left and right
slots to verify vertical position and gain. And I ran through the volts/div
ranges with a PG506 in both slots. Both producing accurate and sharp
traces. But that doesn't guarantee the 5CT1N is happy, does it. The shorted
tantalum decoupling cap was right next to the center slot, for what that's
worth. I replaced it with a 50v tantalum with the same 1uF value.

I'll have to run through a 5CT1N check-out in the 5440, now that you've
brought that up Harvey. Thanks for the suggestion.
Dave


On Tuesday, June 15, 2021, 07:22:50 AM PDT, Harvey White <
madyn@dragonworks.info> wrote:

You might want to check on this, but the 5000 series plugins and the
5400 series plugins were not supposed to be interchangeable. I think you
certainly couldn't use a 5400 series in a 5000, and I *think* that the
reverse is true.

They are not the same scope series, from what I know.

Fat blurry traces indicates that the supply voltages are off, the HV is
likely strange, etc. Not sure, but I'd do a very close read on the manual.

Harvey


On 6/15/2021 1:25 AM, Dave Peterson via groups.io wrote:
To wrap this case:

I ordered a set of replacement MJE800 equivalents from Mouser for
6-bucks-n-change. Got a few nice Pomona jumpers with micro-grabbers to
justify the shipping.

Walter suggested offline that my problem was more likely a short
downstream. Guess what: Walter's a good guesser. The issue turned out to be
a shorted 1uF tantalum decoupling cap on the main interface board on the
-30v supply. As a reminder: the blazing hot MJE800 was the -15v supply.
Odd, but lesson learned: interacting regulators may do unexpected things.

This was part of a electrolytic recapping and 152-0488-00 replacement.
Not necessarily bad, but one of those, "while I'm in there I might as well
..." exercises.

With everything reassembled the PS came up fine on the bench with a
variac and meters wired up to monitor ac and dc voltages and currents.
Everything came up with no problem and supply current stayed down around
150mV. Regulated voltages were a bit over-range, but unloaded.

After reassembling the scope I was able to run through the calibration
procedure. +/- 30v supplies came down to in-range and adjusted to within
10mv. Other supplies are now in spec. I now have a nicely working 5440
scope.

However, and I haven't figured out why yet, the original purpose of this
scope was to run a 5CT1N curve tracer. The curve tracer works nicely (very
sharp traces) in a 5111A, but in the 5440, which otherwise works at full BW
with clean traces, produces fat ugly blurry curve tracer lines. WTF? A
puzzle to be solved. Rather frustrating after all the work.

One final lesson learned in this exercise: plug-in curve tracers are
relatively low power small signal devices. The Q880 that I thought was
shorted was just under driven by the 5CT1N. It can only go up to 20mA Ic,
but the MJE800 Darlington transistors drive 4A with several hundred mA Ibe.
The plug-in can only put out 1mA steps at most. And being Darlingtons they
also have an elevated Vbe, which seemed to not function at all at low Ibe
steps. What I interpreted as a shorted collector-emitter was just the first
step driving full vertical range. More careful examination of the MJE800
datasheet and curve tracer settings showed the transistor actually never
even got out of saturation. To a 5CT1N it does kind of look like a short.
Beginners, eh?

Thanks to all who helped, and hope my lessons learned help others down
the road.
Dave















Re: Tek 2230, almost fixed but with a problem out of my competences

Pitpat
 

I've just measured the resistance across C9410 (storage board) and got around 175ohm (low?) in both 1k and 4k mode


Re: Tek 2230, almost fixed but with a problem out of my competences

Pitpat
 

Also I've measured between C6441(also C6440 and C6442) and gnd a resistance of about 4.9 kohm (board A11A2 ).


7104 versions, and vertical amplifier issue

cmjones01
 

A couple of years ago I picked up a 7104 with the full set of plugins
(7B10, 7B15 and two 7A29s, one of which has the elusive option 04
variable delay) at a bargain price in an industrial disposal auction.
I didn't have time to do anything with it at the time and so put it in
the attic. I've just got it out again and experimented with it a bit.
The good news is that quite a lot of it seems to work. I've had a
trace and readout on the screen. All the controls and the plugin
connectors need a good dose of contact cleaner, as is to be expected,
but there's a more persistent fault.

The vertical deflection only seems to work about half the time. It
either works normally, or everything gets shunted up above the top of
the screen. The beam finder reveals that everything's still there,
just too high to see. With the beam finder enabled, I can see that
trying to move the trace downwards with the Y plugins' vertical
position control first moves it downwards, until about half way, then
it starts moving up again. At no point is it visible without the beam
finder.

I've checked the power test points on the vertical deflection board
under the fault condition, and all rails (+50/+15/+5/-15/-50) are
fine.

While I'm here, are there multiple versions of the 7104 hardware?
Because my scope seems to have a different vertical board to the one
in the paper manual I've got. The one in the manual has fewer Hypcon
devices than mine has, and at least one connector is numbered
differently.

Thank you
Chris


Re: Tek 2230, almost fixed but with a problem out of my competences

Pitpat
 

Hi, it's been quite a while!
Yes albert you are once again right i confirmed your theory about the Miller C. the floating volatages becames progressively faster with the sweep setting, I guess i've followed the wrong white rabbit...
I've noticed that some of the 1k A mode sweep readout got unlocked and now all the settings seems to work (in this particular configuration) with the exception of the slowest ones (0.1s 0.2s 0.5s)
I'm now suspecting something in the 1k/4k selector ciruitry... I'm still quite bothered by toose slightly low ARES1 voltages....
What do you think?


Re: RSA3308A Update

Bruce Lane
 

No worries. I've since located the manufacturer of the board, and got a
user manual. As for the SSD, I have some already. It'll be cheaper to do
a PATA/SATA adapter than go for an actual PATA SSD.

Thanks.

On 15-Jun-21 09:33, nj902 wrote:
I am sorry I won't be able to disassemble my unit to inspect the CPU.

I don't believe there was any obvious difference in appearance between the board in the machine and the drawings in the service manual.

The machine is running on an SSD. Finding a new one of the right size with a parallel interface was easier back when I got my instrument.

There is one on ebay now.

eBay item number:
203101179448
--
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)


Re: PG506 repair question.

Andy Warner
 

The first round of candidates for Q745/755 in the PG506 high amplitude
output section arrived today.
I have uploaded screenshots using the BD179G parts.

https://groups.io/g/TekScopes/photo/265034/3246294 is 10us period,
amplitude max, terminated into 1MOhm.
https://groups.io/g/TekScopes/photo/265034/3246295 is the same, but
terminated into 50Ohm.

The good news is that the full amplitude output is now restored, I think
Ozan's current-based analysis was right on the money here, and without the
ability to dump the current with both transistors, the full output voltage
swing was not possible.

Note the rise and fall times, which preclude the 1us period being any use
at all - the amplitude of the output signal is limited by the rise and fall
times.
This is clearly shown in https://groups.io/g/TekScopes/photo/265034/3246296

I think I clearly need to look for faster parts than the BD179G. That has
an F(t) of 3MHz, while the venerable old D40E7 has F(t) of 230MHz.
I think I have one more chance at reworking the Q745/755 pads before I
start lifting traces.

As an aside, the aberration on the falling edge at low frequencies (which I
now accept as a fact of life) goes away when terminated in 50Ohm.

On Tue, Jun 15, 2021 at 11:44 AM Andy Warner <andyw@pobox.com> wrote:

I have another off list confirmation that the falling edge of the high
amplitude waveform, at least on first gen PG506's, routinely has an
aberration as shown in: https://groups.io/g/TekScopes/photo/265034/3242704
The exact period & amplitude it kicks in at varies between units, but for
the next person that trips over this: it seems like it is just part of the
design, and the rising edge is the one that matters for this particular
unit's role in life.

On Mon, Jun 14, 2021 at 9:14 PM Andy Warner <andyw@pobox.com> wrote:

Thanks for the additional verification, and advice on diodes.

Given the data points from the group, I plan to ignore the falling edge
artifact, and focus on getting the amplitude correct once I have
replaced D745/755 with modern parts.

On Mon, Jun 14, 2021 at 8:07 PM Tom Norman <jtnorman@fire2wire.com>
wrote:

HI Andy-

I wanted to follow through on my earlier response. My PG is serial
B035037, so similar to Dan's I think. It also shows the same negative
going edge distortion you show in your posted picture at 100 Hz, and
pretty
well cleans up around 250 Hz. Output voltage into 1 Meg is 64V P-P, at
maximum amplitude setting, across the frequency range of the
instrument.

I too saw the reference to the rising edge being the "reference" edge,
so
after repairing the PS issue, I just accepted that they (Tek designers)
didn't care too much about what was happening to the negative going
edge
at
longer periods. It's good to know that at least two of you are seeing
a
similar thing. My ignorance is keeping me from understanding why the
designers would have chosen to regulate the entire switching supply
rather
than just locally regulating a fixed -72 rail.

And on the -72 supply diode replacement, I ended up just trying some
1N914
diodes, which seem to have worked well. Also used those to replace
CR80
and CR125, which had taken an absolute beating as a result of the
strange
switching transients that resulted from the "backflow" due to the slow
rectifier recovery times. 1N4148 seems like it would work too.

Tom






--
Andy





--
Andy





--
Andy


Re: Type 284

Chris van Lint
 

Gidday,

As I mentioned, I am downsizing.  I have a 284 in perfect working condition and before ditching the non working one I thought to check if someone wants to have a go at fixing it. I think I have got a prospect in Melbourne.

Cheers,

Chris

On 16/06/2021 06:09, Stephen Bell wrote:
Why not try fixing it? The 284 is a very useful piece of gear for calibrating or adjusting high performance scopes.

I repaired mine a couple of days ago and it wasn't too difficult - just cleaning up a few switch connections and the internal connections in the air line.

If you do part it out definitely save the air line with the tunnel diode assembly and termination resistor assembly. Both items are unobtainium and I am sure another forum member could use these to repair their own 284s.




Re: Type 284

Stephen Bell
 

Why not try fixing it? The 284 is a very useful piece of gear for calibrating or adjusting high performance scopes.

I repaired mine a couple of days ago and it wasn't too difficult - just cleaning up a few switch connections and the internal connections in the air line.

If you do part it out definitely save the air line with the tunnel diode assembly and termination resistor assembly. Both items are unobtainium and I am sure another forum member could use these to repair their own 284s.


Re: 491 Spectrum Analyzer with Custom Modifications

Miguel Work
 

Hi! Is your 491 complete? With cover and all the mixers attenuators and cables? -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Dick Benson Enviado el: martes, 15 de junio de 2021 16:34 Para: TekScopes@groups.io Asunto: Re: [TekScopes] 491 Spectrum Analyzer with Custom Modifications Jeff, >> I'm just curious if anyone can shed some light on what the >> modification >> is and does (or if anyone on this group was the >> purchaser, because that would be cool.) I suspect the "Custom Modifications" are that abomination sitting on top of the analyzer. But, that said, there are no obvious connections. >> I was not the purchaser (sadly, the price was very good). I have a working, stock (unmodified) 491 that I would be happy to sell you for $290 plus shipping. I am located near San Jose CA. Contact me off list if interested. Dick Benson Sent from a Virus, Logic, and Mask Free Bunker deep within The Utopian State of California Scanned by McAfee and confirmed virus-free. Find out more here: https://bit.ly/2zCJMrO


Re: 491 Spectrum Analyzer with Custom Modifications

Miguel Work
 

It seems like a FM AM demodulator with manual tuning switch and tuning pot. I have two 491, is an interesting artefact :) https://entangledwaves.wordpress.com/2014/07/09/tektronix-491-spectrum-analyzer-teardown-and-analysis/ -----Mensaje original----- De: TekScopes@groups.io [mailto:TekScopes@groups.io] En nombre de Jeff Dutky Enviado el: lunes, 14 de junio de 2021 20:33 Para: TekScopes@groups.io Asunto: [TekScopes] 491 Spectrum Analyzer with Custom Modifications I saw this 491 on the auction site yesterday with a custom modification. Pictures here https://groups.io/g/TekScopes/album?id=265112 The listing ended last night. I was not the purchaser (sadly, the price was very good). Here is a link to the original listing https://www.ebay.com/itm/184704993611?nma=true&si=RZU6h9umVBH9zpUNGWIszvRCZ2M%253D&orig_cvip=true&nordt=true&rt=nc&_trksid=p2047675.l2557 I'm just curious if anyone can shed some light on what the modification is and does (or if anyone on this group was the purchaser, because that would be cool) -- Jeff Dutky Scanned by McAfee and confirmed virus-free. Find out more here: https://bit.ly/2zCJMrO


Re: PG506 repair question.

Andy Warner
 

I have another off list confirmation that the falling edge of the high
amplitude waveform, at least on first gen PG506's, routinely has an
aberration as shown in: https://groups.io/g/TekScopes/photo/265034/3242704
The exact period & amplitude it kicks in at varies between units, but for
the next person that trips over this: it seems like it is just part of the
design, and the rising edge is the one that matters for this particular
unit's role in life.

On Mon, Jun 14, 2021 at 9:14 PM Andy Warner <andyw@pobox.com> wrote:

Thanks for the additional verification, and advice on diodes.

Given the data points from the group, I plan to ignore the falling edge
artifact, and focus on getting the amplitude correct once I have
replaced D745/755 with modern parts.

On Mon, Jun 14, 2021 at 8:07 PM Tom Norman <jtnorman@fire2wire.com> wrote:

HI Andy-

I wanted to follow through on my earlier response. My PG is serial
B035037, so similar to Dan's I think. It also shows the same negative
going edge distortion you show in your posted picture at 100 Hz, and
pretty
well cleans up around 250 Hz. Output voltage into 1 Meg is 64V P-P, at
maximum amplitude setting, across the frequency range of the instrument.

I too saw the reference to the rising edge being the "reference" edge, so
after repairing the PS issue, I just accepted that they (Tek designers)
didn't care too much about what was happening to the negative going edge
at
longer periods. It's good to know that at least two of you are seeing a
similar thing. My ignorance is keeping me from understanding why the
designers would have chosen to regulate the entire switching supply
rather
than just locally regulating a fixed -72 rail.

And on the -72 supply diode replacement, I ended up just trying some
1N914
diodes, which seem to have worked well. Also used those to replace CR80
and CR125, which had taken an absolute beating as a result of the strange
switching transients that resulted from the "backflow" due to the slow
rectifier recovery times. 1N4148 seems like it would work too.

Tom






--
Andy





--
Andy


Re: RSA3308A Update

nj902
 

I am sorry I won't be able to disassemble my unit to inspect the CPU.

I don't believe there was any obvious difference in appearance between the board in the machine and the drawings in the service manual.

The machine is running on an SSD. Finding a new one of the right size with a parallel interface was easier back when I got my instrument.

There is one on ebay now.

eBay item number:
203101179448


Re: 491 Spectrum Analyzer with Custom Modifications

nj902
 

The 491 is an interesting historical artifact.

For that purpose, you would be far better off with an un-molested one like Dick has.


Re: 5440 PS transistor selection

Dave Peterson
 

Thanks Harvey,

I did discover the plug-in incompatibility when I tried installing the 5440 plug-ins in the 5111A. Jeff Dutky pointed me to the pertinent section of the Tek Wiki that describes this.

In that I also found that the 5111A plug-ins are "forward compatible" and work in the 5440. I was a tad surprised to see the 5A26 from the 5111A gave readouts on the 5440. While tuning up the 5440, on a lark, I used the 5A26 from the 5111A and the 5A48 from the 5440 to prove I could get four channels showing at once with 5 readouts. The time base is a delayed 5B42, but can't do "dual" A/B sweeps. (That'd be 8 sweeps! :P) But it did prove the scope could do the 4 channels. FWIW. I don't have much experience with these scopes, so I don't even know if a dual delayed sweep time base is available or possible. I rather doubt it. So I don't think there's a lower-right quadrant readout to be had. I digress. Readouts are a whole other thread!

The calibration procedure in the 5440 manual is rather brief, but it does include a HV voltage check, which was within spec. The 5A48 need some very slight tweaking to bring CH1 & CH2 into agreement and get the step attenuator adjustments spot on. Once it was tuned it did very well with edge compensation and provides very nice sharp traces across the volts/div range. Noise, of course, shows up below 5mV/div. But that's to be expected (see my other posts about my large FM interference from local broadcast tower).

The horizontal cal seems a bit deficient, and the time base should be calibrated too. It also has some knob damage to the delayed time/div portion that I'll need to fix. And some switch maintenance. It'll need to be partially disassembled to get at them. These issues are minor and don't appear to affect the horizontal performance. The timing accuracy and stability are good.

Perhaps I need to check the 5CT1N supplies in the center slot of the 5440? Could it be a supply issue in the curve tracer? The cal does have one swapping the vertical plug-in back and forth between the left and right slots to verify vertical position and gain. And I ran through the volts/div ranges with a PG506 in both slots. Both producing accurate and sharp traces. But that doesn't guarantee the 5CT1N is happy, does it. The shorted tantalum decoupling cap was right next to the center slot, for what that's worth. I replaced it with a 50v tantalum with the same 1uF value.

I'll have to run through a 5CT1N check-out in the 5440, now that you've brought that up Harvey. Thanks for the suggestion.
Dave

On Tuesday, June 15, 2021, 07:22:50 AM PDT, Harvey White <madyn@dragonworks.info> wrote:

You might want to check on this, but the 5000 series plugins and the
5400 series plugins were not supposed to be interchangeable. I think you
certainly couldn't use a 5400 series in a 5000, and I *think* that the
reverse is true.

They are not the same scope series, from what I know.

Fat blurry traces indicates that the supply voltages are off, the HV is
likely strange, etc.  Not sure, but I'd do a very close read on the manual.

Harvey


On 6/15/2021 1:25 AM, Dave Peterson via groups.io wrote:
To wrap this case:

I ordered a set of replacement MJE800 equivalents from Mouser for 6-bucks-n-change. Got a few nice Pomona jumpers with micro-grabbers to justify the shipping.

Walter suggested offline that my problem was more likely a short downstream. Guess what: Walter's a good guesser. The issue turned out to be a shorted 1uF tantalum decoupling cap on the main interface board on the -30v supply. As a reminder: the blazing hot MJE800 was the -15v supply. Odd, but lesson learned: interacting regulators may do unexpected things.

This was part of a electrolytic recapping and 152-0488-00 replacement. Not necessarily bad, but one of those, "while I'm in there I might as well ..." exercises.

With everything reassembled the PS came up fine on the bench with a variac and meters wired up to monitor ac and dc voltages and currents. Everything came up with no problem and supply current stayed down around 150mV. Regulated voltages were a bit over-range, but unloaded.

After reassembling the scope I was able to run through the calibration procedure. +/- 30v supplies came down to in-range and adjusted to within 10mv. Other supplies are now in spec. I now have a nicely working 5440 scope.

However, and I haven't figured out why yet, the original purpose of this scope was to run a 5CT1N curve tracer. The curve tracer works nicely (very sharp traces) in a 5111A, but in the 5440, which otherwise works at full BW with clean traces, produces fat ugly blurry curve tracer lines. WTF? A puzzle to be solved. Rather frustrating after all the work.

One final lesson learned in this exercise: plug-in curve tracers are relatively low power small signal devices. The Q880 that I thought was shorted was just under driven by the 5CT1N. It can only go up to 20mA Ic, but the MJE800 Darlington transistors drive 4A with several hundred mA Ibe. The plug-in can only put out 1mA steps at most. And being Darlingtons they also have an elevated Vbe, which seemed to not function at all at low Ibe steps. What I interpreted as a shorted collector-emitter was just the first step driving full vertical range. More careful examination of the MJE800 datasheet and curve tracer settings showed the transistor actually never even got out of saturation. To a 5CT1N it does kind of look like a short. Beginners, eh?

Thanks to all who helped, and hope my lessons learned help others down the road.
Dave






Re: 491 Spectrum Analyzer with Custom Modifications

Dick Benson
 

Jeff,

I'm just curious if anyone can shed some light on what the modification
is and does (or if anyone on this group was the
purchaser, because that would be cool.)

I suspect the "Custom Modifications" are that abomination sitting on top of
the analyzer. But, that said, there are no obvious connections.

I was not the purchaser (sadly, the price was very good).
I have a working, stock (unmodified) 491 that I would be happy to sell you
for $290 plus shipping.

I am located near San Jose CA. Contact me off list if interested.

Dick Benson



Sent from a Virus, Logic, and Mask Free Bunker deep within
The Utopian State of California


Re: 5440 PS transistor selection

Harvey White
 

You might want to check on this, but the 5000 series plugins and the 5400 series plugins were not supposed to be interchangeable. I think you certainly couldn't use a 5400 series in a 5000, and I *think* that the reverse is true.

They are not the same scope series, from what I know.

Fat blurry traces indicates that the supply voltages are off, the HV is likely strange, etc.  Not sure, but I'd do a very close read on the manual.

Harvey

On 6/15/2021 1:25 AM, Dave Peterson via groups.io wrote:
To wrap this case:

I ordered a set of replacement MJE800 equivalents from Mouser for 6-bucks-n-change. Got a few nice Pomona jumpers with micro-grabbers to justify the shipping.

Walter suggested offline that my problem was more likely a short downstream. Guess what: Walter's a good guesser. The issue turned out to be a shorted 1uF tantalum decoupling cap on the main interface board on the -30v supply. As a reminder: the blazing hot MJE800 was the -15v supply. Odd, but lesson learned: interacting regulators may do unexpected things.

This was part of a electrolytic recapping and 152-0488-00 replacement. Not necessarily bad, but one of those, "while I'm in there I might as well ..." exercises.

With everything reassembled the PS came up fine on the bench with a variac and meters wired up to monitor ac and dc voltages and currents. Everything came up with no problem and supply current stayed down around 150mV. Regulated voltages were a bit over-range, but unloaded.

After reassembling the scope I was able to run through the calibration procedure. +/- 30v supplies came down to in-range and adjusted to within 10mv. Other supplies are now in spec. I now have a nicely working 5440 scope.

However, and I haven't figured out why yet, the original purpose of this scope was to run a 5CT1N curve tracer. The curve tracer works nicely (very sharp traces) in a 5111A, but in the 5440, which otherwise works at full BW with clean traces, produces fat ugly blurry curve tracer lines. WTF? A puzzle to be solved. Rather frustrating after all the work.

One final lesson learned in this exercise: plug-in curve tracers are relatively low power small signal devices. The Q880 that I thought was shorted was just under driven by the 5CT1N. It can only go up to 20mA Ic, but the MJE800 Darlington transistors drive 4A with several hundred mA Ibe. The plug-in can only put out 1mA steps at most. And being Darlingtons they also have an elevated Vbe, which seemed to not function at all at low Ibe steps. What I interpreted as a shorted collector-emitter was just the first step driving full vertical range. More careful examination of the MJE800 datasheet and curve tracer settings showed the transistor actually never even got out of saturation. To a 5CT1N it does kind of look like a short. Beginners, eh?

Thanks to all who helped, and hope my lessons learned help others down the road.
Dave





Re: Challenging 2465 PS repair

satbeginner
 

Sorry Siggi,

I forgot to mention you as well, it was your remark that led me into checking the actual situation with the two fuses and connectors.

However, at the moment I am nowhere near checking the 5VD...

Again, thanks,

Leo


Re: Challenging 2465 PS repair

satbeginner
 

Hi Ozan, Jon,

I did not have time the last few days, but I hope to look further today.

I can confirm the triangle is at the switching frequency.
The 594 is at roughly a 20uS period, and the secondary part is at double that time, the 4013 is dividing that nicely, so appr. 40uS.

My last test was to go backwards in the flowchart, so I connected the Regulator board, and powerup the combo, and switched it off really quick ;-) because of some smoke.

It came from the LR1060 and R1072, so I have to check some more :-)

My plan for this afternoon is:

Remove a working Power Supply from one of my 2465's, and split the boards and perform the test using just the Primary Load to check for that ripple. so we know if the manual is right or not.

BTW, I figured out what the description means by using TWO 2Ohm resistors:
The manual says to connect them to connectors J232 and J303 between the 5V and Gnd.

Well: my PS board does have the 2 fuses, but only the J232, connector J303 is not there, the tracks and space to mount a connector is there, but the space is empty, and based on the solder, was never there.
So I think the PS should be able to run just fine during test with One 2 Ohm resistor as load, but I can connect the second one behind the second fuse just as a check.

Thanks for your feedback, to be continued,

Leo

3701 - 3720 of 187116