Date   

Re: tektronics 2465b 400mhz nvram battery info

Chuck Harris <cfharris@...>
 

By "the rest" I mean the rest of the 256 words
in the block.

-Chuck Harris

Chuck Harris wrote:

If your copy program uses any ram, it will put
its very own data in the NVRAM.

The NVRAM is mostly used as the data space for
the CPU, ... data, heap, stack..., and as such is
refreshed every time the scope is powered up.
There is only a very small portion (170 14bit words)
that is calibration constants. I would suggest that
the rest is the front panel state, and the timers,
and a checksum.

-Chuck Harris

ADas via Groups.Io wrote:
Hi SImone,
What you are describing is right way to use the copy program. It doesn't matter which program "ramhigh.dat" or "ramlow.dat" is run first since they copy independently the upper half and lower half of the old nvram memory locations. . Remember once one of the programs is run, which is on the fresh nvram, take the fresh nvram out, read it with the programmer to obtain data from locations 200hex to 11ff hex inclusive. The data from these locations obtained using "ramhigh.dat" contain copy the upper 4000 decimal bytes of the old nvram and "ramlow.dat" will contain the lower 4000 decimal bytes. Once the copied data (on the fresh nvram) is copied out using the programmer, program the "ramhigh.dat" (assuming ramlow.dat used first), into the fresh nvram and repeat the procedure described to obtain the second half of the old nvram contents.
cheers
Das



Re: tektronics 2465b 400mhz nvram battery info

Chuck Harris <cfharris@...>
 

If your copy program uses any ram, it will put
its very own data in the NVRAM.

The NVRAM is mostly used as the data space for
the CPU, ... data, heap, stack..., and as such is
refreshed every time the scope is powered up.
There is only a very small portion (170 14bit words)
that is calibration constants. I would suggest that
the rest is the front panel state, and the timers,
and a checksum.

-Chuck Harris

ADas via Groups.Io wrote:

Hi SImone,
What you are describing is right way to use the copy program. It doesn't matter which program "ramhigh.dat" or "ramlow.dat" is run first since they copy independently the upper half and lower half of the old nvram memory locations. . Remember once one of the programs is run, which is on the fresh nvram, take the fresh nvram out, read it with the programmer to obtain data from locations 200hex to 11ff hex inclusive. The data from these locations obtained using "ramhigh.dat" contain copy the upper 4000 decimal bytes of the old nvram and "ramlow.dat" will contain the lower 4000 decimal bytes. Once the copied data (on the fresh nvram) is copied out using the programmer, program the "ramhigh.dat" (assuming ramlow.dat used first), into the fresh nvram and repeat the procedure described to obtain the second half of the old nvram contents.
cheers
Das


Re: 7B53A broken switch (mixed mode switch)

Fabio Trevisan
 

Hello Max and Phil,
I've been recently through a very similar case, to the exception that on my 7B53A, the upper part of the switch, as well as the rolling golden contact pin, and its pressure spring, were all still present... on;y that the switch was already open on one side.
I posted pictures back than that you can still see here:
https://groups.io/g/TekScopes/album?id=35474

To Phil, if you're to disassemble your parts 7B53A to get a switch to Max, I endorse what Max said; it's simple to detach the "A6-Sweep Circuit Board" from the back of the "A1 Interface Circuit Board", to get access to the solder pads of the switch and further endorse that, putting it back together is the hardest part, because you will need to align some 20 pins on different spots of the two boards, in order to be able to pull them together again... But if it's a parts unit, maybe you won't want to have all the trouble... just keep the boards apart, or bend the pins.

To Max, my advice to you is, while crimping the tabs of the upper metal cover back in place, around the switch's bottom part to hold them both together, be careful and don't apply too much pressure on the plier. The bottom part looks like plastic, but it's bakelite, and as you know, it's hard and strong, but it breaks easily.
I managed to break mine and I had to be creative to glue the two broken pieces into one again, in a way that would stand being crimped and yet, survive the day-to-day stress... I think I was lucky and it ended up well, but you better be cautious while crimping the metal tabs back, around the bakelite bottom piece.

all the best,
Fabio


Re: tektronics 2465b 400mhz nvram battery info

Gif Sim
 

thank you
Das

the most complicated part for my skills
is the combination ,with hex editor , of the two halves obtained with your program


I'm waiting for all the components and then I'll try
you did a great job
I think it's the simplest and easiest method of all

thank you very much for the help you give on the group !!

Simone


Il 10 aprile 2018 alle 21.52 "ADas via Groups.Io" <amitabhad@...> ha scritto:

Hi SImone,
What you are describing is right way to use the copy program. It doesn't matter which program "ramhigh.dat" or "ramlow.dat" is run first since they copy independently the upper half and lower half of the old nvram memory locations. . Remember once one of the programs is run, which is on the fresh nvram, take the fresh nvram out, read it with the programmer to obtain data from locations 200hex to 11ff hex inclusive. The data from these locations obtained using "ramhigh.dat" contain copy the upper 4000 decimal bytes of the old nvram and "ramlow.dat" will contain the lower 4000 decimal bytes. Once the copied data (on the fresh nvram) is copied out using the programmer, program the "ramhigh.dat" (assuming ramlow.dat used first), into the fresh nvram and repeat the procedure described to obtain the second half of the old nvram contents.
cheers
Das



Re: 7904 Mainframe damaged

JJ
 

Right Dave. There is enough room to scope the regulator board on top while
the PSU is hanging out the back of the mainframe.

On Tue, Apr 10, 2018 at 4:01 PM, David DiGiacomo <daviddigiacomo@...>
wrote:

I forgot to mention that you don't actually need to build a load board
to work on a 7904 power supply. The cables are long enough that you
can let the PS module trail out the back of the scope onto the bench,
and get decent access to most of it.




Re: 7904 Mainframe damaged

JJ
 

Bob, I found that the diodes seem OK when I disconnected one lead and
measured both resistance and diode forward and reverse voltage. I found
that the short across those two diodes was due to a shorted capacitor on
the rectifier board - I was actually measuring the winding tap resistance
through a weird path. I reconnected the PSU back into the mainframe after
changing the cap. There was no glory - a very low tick coming from the
supply.

I'll need to continue debug by following the procedure in the that
document. I measured the resistances in z-axis board as the procedure
indicates while the PSU was out of the mainframe - they are pretty much in
line - a couple of resistances were much higher than the table - none were
lower . I'll measure them now while the power supply is in the mainframe,
Also, I get different results using a VOM and a DVM. Maybe there's
something wrong with my VOM - it's pretty old. Is a VOM required to get the
proper measurements as indicated in the table?

.Best,
John

On Tue, Apr 10, 2018 at 2:41 PM, Robert Hay <bobh@...> wrote:

They say in the article that a low resistance indicates a problem in the
mainframe which is true if you are looking at something shorting to
ground. But, in your case I would not discount that high current caused a
open circuit while trying to get back to the source. I suppose you already
looked for any signs of burning or smoked components, leads, traces, etc.

Bob.



On 4/10/2018 7:44 AM, JJ wrote:

Yes the resistances were very high. According to that doc, the issue
should
be on the PSU. I'm going to put the PSU back into the mainframe, connect
the cables, and make those voltage measurements on the LV regulator board.
I didn't check for voltages before taking the PSU out because I didn't
know
at that time that the PSU needs to be under minimum load.

I found a shorted cap C1360 on the rectifier board (+54v filter cap on
output of Pi filter). I'm going to lift one lead to ensure it's the
problem. I'm also going to validate that the two power diodes that I found
are shorted - by disconnecting the wires going to those diodes and
measuring. If the diodes are bad, I'll replace the bad 10A diodes with two
5A diodes in parallel temporarily - hoping that's OK, I'll then hook up
the
mainframe's cables to the PS and check the voltages. I think the 3 cables
are long enough for the PSU to hang out the back. If not, I plan on making
extender cables.

Best,
John

On Tue, Apr 10, 2018 at 10:16 AM, Robert Hay <bobh@...> wrote:

Have you checked resistances as suggested in the Service Scope article?

And then voltages with the supply outside the scope but still connected?

Bob.


On 4/10/2018 6:38 AM, JJ wrote:

Hi Tony, So, based on your findings, you have confirmed that the the PSU
needs to be under load in order to be functional. I will check all the
caps
on those 3 boards as well. Thank you for the info - it's very, very
helpful.
I hope the experts on this forum can help you out with the remainder of
your 7904's issues.

Best,
John

On Tue, Apr 10, 2018 at 9:29 AM, Yiu On Tony C via Groups.Io <
tonycheung_hk@...> wrote:

Hi JJ :

I am from Hong Kong ! I just complete the repair of PSU of TEK7904 , I
am
lucky , I find a SHORT E-Cap. once I replace it and turn on PSU alone ,
It
still sound shut-down ! once I connect to main unit , it come normal .
I found few E-Cap short on A9 H amp board, A2 Main interface board and
A12 Rectifier board
For the power diode , I did check each by de-solder the to wire only .
My 7904 still have other issue , H ok but the read-out still error in
units , Y are not function -- position knob no response .

RegardTony CheungAPR 10 2018


From: JJ <jajustin@...>
To: TekScopes@groups.io
Sent: Tuesday, April 10, 2018 7:16 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Dave, I went through hundreds of files in the files section of the
archive
and wasn't able to identify the schematic describing the minimum
loading
requirements for power supplies. Tried searching, browsing, ad nauseum!
No
glory. Are you sure that Jerry uploaded it?

Best,
John

On Mon, Apr 9, 2018 at 4:54 PM, Dave Daniel <kc0wjn@...> wrote:

On some of the 7xxx supplies (SMPS supplies, I believe), one needs to
put

a minimum load on the power supply output in order for the supply to

work.
I don't remember if that is true for the 7904 power supply.

Jerry Massengale built one of these loads. I think he uploaded a copy
of
the schematic to the files section back in maybe2015.

DaveD


On 4/9/2018 12:22 PM, JJ wrote:

I removed the power supply from the mainframe - it's on my bench.
First,

I'll remove the wire from the diode terminal and check to see if the

diode
is actually shorted as others have suggested. I was thinking of
replacing
the 10A diodes with two 5A diodes in parallel that I have available in
my
parts bin temporarily to see if I get all the other voltages back -
right
now there are no voltages at the test points of the rectifier board
and

the
low voltage regulator. I wouldn't think there would be that much
load
with
the supply removed? That way I can continue to debug. Thoughts?

On Mon, Apr 9, 2018 at 2:06 PM, Jeff Urban <JURB6006@...>
wrote:

Incidentally, that stuff about the mini EMP is not very likely. Nott

only
does it actually have to happen at a strength to do something, it also

needs to be oriented the right way to do something. Also I erred
about
the
vaporized foil on the board, it was about ½ cm., not inch.

Anyway, if you are sure about the diodes I guess you know what to
do,

if
possible. It might be rough to gt everything hooked back up for a live

test
without actually assembling it. Changing the diodes right away ? You
could
do that. And of course watch for mounting screws that also function
as

a
ground, that has tripped me up a couple of times.

Since you have one + and one - diode bad, assuming you don't have a

short
to ground, I would check see if there is a short between the + and -

legs
of that supply. At this time I have no idea what those sources feed
but

it
could be a series arranged push pull output to something and while
both
of
the output devices could be shorted, the load isn't low enough

impedance,
or maybe even electrostatic, to read a short to ground. It happens.















Re: 7904 Mainframe damaged

David DiGiacomo
 

I forgot to mention that you don't actually need to build a load board
to work on a 7904 power supply. The cables are long enough that you
can let the PS module trail out the back of the scope onto the bench,
and get decent access to most of it.


Re: 7904 Mainframe damaged

David DiGiacomo
 

On Tue, Apr 10, 2018 at 5:15 AM, JJ <jajustin@...> wrote:
Dave, I went through hundreds of files in the files section of the archive
and wasn't able to identify the schematic describing the minimum loading
requirements for power supplies. Tried searching, browsing, ad nauseum! No
glory. Are you sure that Jerry uploaded it?
There was nothing uploaded, it was a short and sweet message:

I used 4 ohms on both 5V, 20 on both 15V, and 500 on both 50V. It is
not critical, you could probably get by with only 2 ohms on 5v.

Jerry Massengale


Re: tektronics 2465b 400mhz nvram battery info

ADas
 

Hi SImone,
What you are describing is right way to use the copy program. It doesn't matter which program "ramhigh.dat" or "ramlow.dat" is run first since they copy independently the upper half and lower half of the old nvram memory locations. . Remember once one of the programs is run, which is on the fresh nvram, take the fresh nvram out, read it with the programmer to obtain data from locations 200hex to 11ff hex inclusive. The data from these locations obtained using "ramhigh.dat" contain copy the upper 4000 decimal bytes of the old nvram and "ramlow.dat" will contain the lower 4000 decimal bytes. Once the copied data (on the fresh nvram) is copied out using the programmer, program the "ramhigh.dat" (assuming ramlow.dat used first), into the fresh nvram and repeat the procedure described to obtain the second half of the old nvram contents.
cheers
Das


Re: tektronics 2465b 400mhz nvram battery info

Gif Sim
 

ciao mirco

what programmer do you use for nvram?


I'm not very experienced with the programming
I'm waiting for all the components to arrive
then I will try with the method tested by adas

which I think is the easiest method


saluti
Simone Minelli


Il 10 aprile 2018 alle 20.49 "zoldanmirco via Groups.Io" <zoldanmirco@...> ha scritto:

Ciao Das

Thanks for your help now I get everything I need and I go with the procedure that you have
tested, in the next few days I communicate the results.
Ciao
Mirco



Re: tektronics 2465b 400mhz nvram battery info

zoldanmirco@...
 

Ciao Das

Thanks for your help now I get everything I need and I go with the procedure that you have
tested, in the next few days I communicate the results.
Ciao
Mirco


Re: 7904 Mainframe damaged

bobh@joba.com
 

They say in the article that a low resistance indicates a problem in the mainframe which is true if you are looking at something shorting to ground.  But, in your case I would not discount that high current caused a open circuit while trying to get back to the source.  I suppose you already looked for any signs of burning or smoked components, leads, traces, etc.

Bob.

On 4/10/2018 7:44 AM, JJ wrote:
Yes the resistances were very high. According to that doc, the issue should
be on the PSU. I'm going to put the PSU back into the mainframe, connect
the cables, and make those voltage measurements on the LV regulator board.
I didn't check for voltages before taking the PSU out because I didn't know
at that time that the PSU needs to be under minimum load.

I found a shorted cap C1360 on the rectifier board (+54v filter cap on
output of Pi filter). I'm going to lift one lead to ensure it's the
problem. I'm also going to validate that the two power diodes that I found
are shorted - by disconnecting the wires going to those diodes and
measuring. If the diodes are bad, I'll replace the bad 10A diodes with two
5A diodes in parallel temporarily - hoping that's OK, I'll then hook up the
mainframe's cables to the PS and check the voltages. I think the 3 cables
are long enough for the PSU to hang out the back. If not, I plan on making
extender cables.

Best,
John

On Tue, Apr 10, 2018 at 10:16 AM, Robert Hay <bobh@...> wrote:

Have you checked resistances as suggested in the Service Scope article?

And then voltages with the supply outside the scope but still connected?

Bob.


On 4/10/2018 6:38 AM, JJ wrote:

Hi Tony, So, based on your findings, you have confirmed that the the PSU
needs to be under load in order to be functional. I will check all the
caps
on those 3 boards as well. Thank you for the info - it's very, very
helpful.
I hope the experts on this forum can help you out with the remainder of
your 7904's issues.

Best,
John

On Tue, Apr 10, 2018 at 9:29 AM, Yiu On Tony C via Groups.Io <
tonycheung_hk@...> wrote:

Hi JJ :
I am from Hong Kong ! I just complete the repair of PSU of TEK7904 , I am
lucky , I find a SHORT E-Cap. once I replace it and turn on PSU alone ,
It
still sound shut-down ! once I connect to main unit , it come normal .
I found few E-Cap short on A9 H amp board, A2 Main interface board and
A12 Rectifier board
For the power diode , I did check each by de-solder the to wire only .
My 7904 still have other issue , H ok but the read-out still error in
units , Y are not function -- position knob no response .

RegardTony CheungAPR 10 2018


From: JJ <jajustin@...>
To: TekScopes@groups.io
Sent: Tuesday, April 10, 2018 7:16 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Dave, I went through hundreds of files in the files section of the
archive
and wasn't able to identify the schematic describing the minimum loading
requirements for power supplies. Tried searching, browsing, ad nauseum!
No
glory. Are you sure that Jerry uploaded it?

Best,
John

On Mon, Apr 9, 2018 at 4:54 PM, Dave Daniel <kc0wjn@...> wrote:

On some of the 7xxx supplies (SMPS supplies, I believe), one needs to put
a minimum load on the power supply output in order for the supply to
work.

I don't remember if that is true for the 7904 power supply.

Jerry Massengale built one of these loads. I think he uploaded a copy of
the schematic to the files section back in maybe2015.

DaveD


On 4/9/2018 12:22 PM, JJ wrote:

I removed the power supply from the mainframe - it's on my bench. First,
I'll remove the wire from the diode terminal and check to see if the
diode
is actually shorted as others have suggested. I was thinking of
replacing
the 10A diodes with two 5A diodes in parallel that I have available in
my
parts bin temporarily to see if I get all the other voltages back -
right
now there are no voltages at the test points of the rectifier board and
the
low voltage regulator. I wouldn't think there would be that much load
with
the supply removed? That way I can continue to debug. Thoughts?

On Mon, Apr 9, 2018 at 2:06 PM, Jeff Urban <JURB6006@...> wrote:

Incidentally, that stuff about the mini EMP is not very likely. Nott
only
does it actually have to happen at a strength to do something, it also
needs to be oriented the right way to do something. Also I erred about
the
vaporized foil on the board, it was about ½ cm., not inch.

Anyway, if you are sure about the diodes I guess you know what to do,
if
possible. It might be rough to gt everything hooked back up for a live
test
without actually assembling it. Changing the diodes right away ? You
could
do that. And of course watch for mounting screws that also function as
a
ground, that has tripped me up a couple of times.
Since you have one + and one - diode bad, assuming you don't have a
short
to ground, I would check see if there is a short between the + and -
legs
of that supply. At this time I have no idea what those sources feed but
it
could be a series arranged push pull output to something and while
both
of
the output devices could be shorted, the load isn't low enough
impedance,
or maybe even electrostatic, to read a short to ground. It happens.











Re: Trying to fix up my 2213A

Fabio Trevisan
 

Hello Lukus,
See some answers next to your questions...

On Sun, Apr 8, 2018 at 05:57 pm, Lukus wrote:
On April 3rd, I picked up a 2213A. While testing it, I noticed that the trace
does not fill the whole display regardless of position settings. I tried
messing around with the controls to see if I could fix it without opening the
scope, but I had no luck doing that.
Also, I found that sometimes a signal was
displayed even when the trace was set to ground.
Indeed it's a weird waveform. Did you try to change the sweep speeds (Time/Div), and or the input attenuator (Volts/Div) settings? Does that change the way that "wave" shows on the screen, this may tell you/us something about where this "signal" is sneaking into the circuits.

The other day, I opened up
the scope (the cover won't come off all the way, but it comes off enough for
me to access the boards) so I could calibrate it. I bought a copy of the 2213A
service manual, and proceeded to adjust the horizontal amplifier gain.
Usually the Tek manuals are very comprehensive and you should get instructions on how to open it properly.

However, even with the gain turned to the max, the trace does not fill the
display. Both the trace after adjusting and the mysterious waveform are shown
here: https://i.imgur.com/46gAXwu.jpg
I wouldn't have jumped directly into changing the scope's calibration, without first checking the basics, and I`m afraid that even doing that, you didn't really ruled out anything.
There are two things that you will see on this forum, which are general and mandatory advice before diving into anything more involving (like fiddling with the calibration adjustments):
1. Check the "so called" low voltage power supplies...(LVPS is everything that is not the C.R.T. High voltages) not necessarily a "low" voltage. Among the low voltages there are usually voltages in the 50~60 volts ballpark, and in the 100~140V ballpark.
1a.for correct voltages (you will need a VoltMeter, at least, and preferably one that you can trust the measurement).
1b. For ripple, and since this is the first oscilloscope you have, I suppose you can't check the ripple and/or power supplies waveforms, so it must suffice you measure the AC voltage of the DC power supplies. Those ripple voltages are usually in the millivolts arena, at most, in the 100ths of volt, so you will need a relatively sensitive AC voltmeter (again that you can trust).

2. Looking for signs of false-contacts or conditions that are usually associated to false-contacts, like signs of corrosion, excess of dust or dirty innards, signs of humidity... and preemptively, trying to clean the easily accessible switches with I.P.A. or contact cleaner. If the latter, make sure you use a contact cleaner that's safe to plastics... The manual is your friend here. Don't apply any cleaner without first checking in the manual if that switch in particular has special recommendations for cleaning. In doubt... don't.
Exercising the switches and potentiometers usually help to clean them, and also reveal if they are showing signs of dirtiness / false contacts. It's common that some lubricants dry out and leave an insulating film that sometimes render the switch or potentiometer totally dead or opened, and often this is not an irreversible condition.
One example to this topic is the "Beam Finder" switch, false contact on it is known to cause this kind of problem (of compressed gain, on either X, or Y axis).

The wave disappears if I ground the shroud surrounding the CRT. I will try to
get the cover off so I can check connections and voltages.
The strange waveform may be nothing, it may just be noise pickup that's happening because the cover is partially opened (so that it's natural connection to ground is broken, as it remains grounded while closed) but at the same time, it's in close range to sensitive electronics that will pickup noise from the nearby big piece of metal... or the cover, while ungrounded, may be picking up strong EMI interference from the Power supply, and transmitting it (by capacitive coupling) to the sensitive parts that it may be nearby.

Can someone help me work through calibrating this scope and getting it to work
properly? For your information, this is my first ever oscilloscope.
You came to the right place. I don't know the 2213 in particular, but surely other folks will jump in and help.

If you want more information and/or details, please let me know; I would be
happy to provide them.
Let us know about the Low Voltage power supply voltages... and if the manual helped you with opening the scope (completely).

By the way, how do I properly reply to a reply on a topic? I tried posting a
reply 3 times the last time I posted, but none of them showed up.
Do you use an e-mail client? or you read / reply directly from Tekscopes Groups.io web interface?
Rgrds,
Fabio


Re: 2235 stuck cover

Ed Breya
 

Sometimes the cans can be a tight fit on the chassis. This can be aggravated by any dents, dings, grit, or corrosion that can make the Al surfaces gall and bind up. Once you are sure all the fasteners are removed, you can apply gentle brute force by placing the scope upright with its back end resting on a piece of carpeting or towels on the floor, and pushing the can downward. Hold the handle knobs on the sides to apply the force. Some rocking and twisting should help to slightly deform the whole thing, breaking any surface bonds.

Ed


Re: tektronics 2465b 400mhz nvram battery info

Mark Litwack
 

The calibration data can be dumped via GPIB, at least on the 2445/2465 and 2445A/2465A. It's not been confirmed it can be done on the 2465B, but I suspect it would work on that too. I'm not aware of an automatic way to dump the whole NVRAM, but the hidden GPIB commands to do it piecemeal have been posted here:

http://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg1449647/#msg1449647

If you (or anyone) try it on the 2465B, let us know if it works or not.

As per that post, the data can also be written. So, if you have a GPIB interface it makes calibration backup and restore much simpler.


Re: 7B53A broken switch (mixed mode switch)

Phillip Potter
 

Hi Max,

I was looking at the cross-connecting pins from the side and not from the bottom, and misinterpreted the connection.

I have been working on replacing or rebuilding the fan on my 453, and have been displeased with how the fan is hardwired to the inside of the scope, rather than having a plug!  It seems crazy to me, made all the more crazy when I pulled one of the wires out (accidentally).  I guess I am (now) expecting the worst from Tek, where, before the fan, was always looking for the excellent engineering and finding it everywhere in every device...

Of course, you are right. I will see what I can do with this tear down and will take your advice about looking at my working 7B53A for that switch "floating" and get it tightened.  I'm wondering if I can't fashion a tool for that job?

Thanks, and I will keep you advised.

Phil

On 4/9/2018 4:14 AM, unclebanjoman wrote:
they are connected via several connectors


Re: 2235 stuck cover

tom jobe <tomjobe@...>
 

You don’t mention the screw on the side, but you do mention two screws being removed after the back cover was off.
I think there are only those two ,the side and bottom screws but I’m not at home to have a look at any 22xx’s

On Apr 10, 2018, at 7:27 AM, Bert Haskins <bhaskins@...> wrote:

I have removed the cover from many 22xx Teks over the years but this one has me stumped.
I've removed the back plastic and the two ( top and bottom ) small screws and the cover is still locked on tight.

Am I cracking up or what?

Thanks,
Bert



Re: 7904 Mainframe damaged

JJ
 

All the resistances with the PSU disconnected from the mainframe are way
higher than those indicated in the "Servicing the 7904 High-efficiency PS"
doc. When I fix the issues that I have found and the resistance
measurements line up with that doc, then I should be good to reconnect the
PSU to the mainframe,

On Tue, Apr 10, 2018 at 10:22 AM, Velik Kazakov via Groups.Io <
velik_kazakov@...> wrote:

On Tue, Apr 10, 2018 at 04:16 am, JJ wrote:


Dave, I went through hundreds of files in the files section of the
archive
and wasn't able to identify the schematic describing the minimum loading
requirements for power supplies. Tried searching, browsing, ad nauseum!
No
glory. Are you sure that Jerry uploaded it?

Best,
John
There have nothing about minimum load, but in the "Servicing the 7904
High-efficiency PS" have the resistance for all of power rails. You can to
calculate the load but, need to make some for all of rails. I do some of
this scopes and first measuring the main frame and when all is in limits
connect the PS to main frame and check all in PS. I find lots of bad caps
in all the boards in the main frame before to start to do the power supply.
If need can try to find a topic in the eevblog for one of this scopes.




Re: 7904 Mainframe damaged

JJ
 

Yes the resistances were very high. According to that doc, the issue should
be on the PSU. I'm going to put the PSU back into the mainframe, connect
the cables, and make those voltage measurements on the LV regulator board.
I didn't check for voltages before taking the PSU out because I didn't know
at that time that the PSU needs to be under minimum load.

I found a shorted cap C1360 on the rectifier board (+54v filter cap on
output of Pi filter). I'm going to lift one lead to ensure it's the
problem. I'm also going to validate that the two power diodes that I found
are shorted - by disconnecting the wires going to those diodes and
measuring. If the diodes are bad, I'll replace the bad 10A diodes with two
5A diodes in parallel temporarily - hoping that's OK, I'll then hook up the
mainframe's cables to the PS and check the voltages. I think the 3 cables
are long enough for the PSU to hang out the back. If not, I plan on making
extender cables.

Best,
John

On Tue, Apr 10, 2018 at 10:16 AM, Robert Hay <bobh@...> wrote:

Have you checked resistances as suggested in the Service Scope article?

And then voltages with the supply outside the scope but still connected?

Bob.


On 4/10/2018 6:38 AM, JJ wrote:

Hi Tony, So, based on your findings, you have confirmed that the the PSU
needs to be under load in order to be functional. I will check all the
caps
on those 3 boards as well. Thank you for the info - it's very, very
helpful.
I hope the experts on this forum can help you out with the remainder of
your 7904's issues.

Best,
John

On Tue, Apr 10, 2018 at 9:29 AM, Yiu On Tony C via Groups.Io <
tonycheung_hk@...> wrote:

Hi JJ :
I am from Hong Kong ! I just complete the repair of PSU of TEK7904 , I am
lucky , I find a SHORT E-Cap. once I replace it and turn on PSU alone ,
It
still sound shut-down ! once I connect to main unit , it come normal .
I found few E-Cap short on A9 H amp board, A2 Main interface board and
A12 Rectifier board
For the power diode , I did check each by de-solder the to wire only .
My 7904 still have other issue , H ok but the read-out still error in
units , Y are not function -- position knob no response .

RegardTony CheungAPR 10 2018


From: JJ <jajustin@...>
To: TekScopes@groups.io
Sent: Tuesday, April 10, 2018 7:16 PM
Subject: Re: [TekScopes] 7904 Mainframe damaged

Dave, I went through hundreds of files in the files section of the
archive
and wasn't able to identify the schematic describing the minimum loading
requirements for power supplies. Tried searching, browsing, ad nauseum!
No
glory. Are you sure that Jerry uploaded it?

Best,
John

On Mon, Apr 9, 2018 at 4:54 PM, Dave Daniel <kc0wjn@...> wrote:

On some of the 7xxx supplies (SMPS supplies, I believe), one needs to put
a minimum load on the power supply output in order for the supply to
work.

I don't remember if that is true for the 7904 power supply.

Jerry Massengale built one of these loads. I think he uploaded a copy of
the schematic to the files section back in maybe2015.

DaveD


On 4/9/2018 12:22 PM, JJ wrote:

I removed the power supply from the mainframe - it's on my bench. First,
I'll remove the wire from the diode terminal and check to see if the
diode
is actually shorted as others have suggested. I was thinking of
replacing
the 10A diodes with two 5A diodes in parallel that I have available in
my
parts bin temporarily to see if I get all the other voltages back -
right
now there are no voltages at the test points of the rectifier board and
the
low voltage regulator. I wouldn't think there would be that much load
with
the supply removed? That way I can continue to debug. Thoughts?

On Mon, Apr 9, 2018 at 2:06 PM, Jeff Urban <JURB6006@...> wrote:

Incidentally, that stuff about the mini EMP is not very likely. Nott
only
does it actually have to happen at a strength to do something, it also
needs to be oriented the right way to do something. Also I erred about
the
vaporized foil on the board, it was about ½ cm., not inch.

Anyway, if you are sure about the diodes I guess you know what to do,
if
possible. It might be rough to gt everything hooked back up for a live
test
without actually assembling it. Changing the diodes right away ? You
could
do that. And of course watch for mounting screws that also function as
a
ground, that has tripped me up a couple of times.

Since you have one + and one - diode bad, assuming you don't have a
short
to ground, I would check see if there is a short between the + and -
legs
of that supply. At this time I have no idea what those sources feed but
it
could be a series arranged push pull output to something and while
both
of
the output devices could be shorted, the load isn't low enough
impedance,
or maybe even electrostatic, to read a short to ground. It happens.















Re: tektronics 2465b 400mhz nvram battery info

Gif Sim
 

hi adas
thank you very much for your information
I think this method of copying is the fastest and most brilliant of all the methods described
I bought the material from digikey
and I'm waiting for delivery

as a programmer I bought the GQ-4x4
that they tell me is compatible with dallas and fram

a little info I ask you:
when I insert the ram with the "ramlow.dat" program, I turn on the oscilloscope
I short circuit pin 1-2 of the cpu,
move the jumper P503
I turn off the oscilloscope
remove the short-circuit pin 1-2 and move the jumper p503
then I repeat the whole sequence with "ramhight.dat"
is the procedure correct?

thanks adas
also by all users who follow the post

regards
Simone


Il 10 aprile 2018 alle 14.03 "ADas via Groups.Io" <amitabhad@...> ha scritto:

Dear TEKScopers,
I am happy to help if the method i used to copy the nvram isnt clear to any one.
A few points that have raised, I can confirm:
Old NVRAM desoldering then attempting to read it is potentially NVRAM corrupting when the ram is very old. Certainly my own experience using a professional grade vacuum desolderer, once i had already copied the old nvram showed corruption of around 50% of the ram locations. This was despite intentionally keeping the desoldering time low to avoid overheating.
If you want to replace the nvram, then buying it from a large distributor is worth it, as there are a lot of fake nvram on ebay, being a expensive part, i imagine its a target for counterfeiting. THe 6802 cpu on the 246x have a 5mhz clock (divided from 10mhz) but the ram cycle time is 1us, so really there should be no problem with 200ns ram.
The copy process i have described is very simple you only need ram programmer. I built my own programmer out of discrete TTL logic, but there are several commercial ones. As chiuck has pointed out the copy is not a recal its just a copy to stop the scope bricking when old nvram loses power.
In regards to combining the two halves of the copied nvram from my program, any hex editor will do, there are tons of them that are freeware. I used one called "HxD"
cheers
ADAS


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