Date   

Re: Another miserable tantalum!

johnlegros
 

yes , a good thing , however they breakdown not to Bad design ,but low Peak voltage rating ,and if ripple IS présent on top of normal désignés voltage , then they breakdown...

Envoyé depuis mon Redmi 4X

Le 1 mai 2020 2:53 PM, Chuck Harris <cfharris@erols.com> a écrit :




Shhh!  Don't tell anyone!

How often can you fix truly complicated looking failures
with just your eyes, nose, and an ohmmeter?

-Chuck Harris

Raymond Domp Frank wrote:
On Fri, May  1, 2020 at 07:21 AM, Dave Seiter wrote:


they would need serious derating in order to keep the failure rate
down.
.... after decades.
We should be grateful for this. After all, it allowed us to acquire
heaps of defective vintage Tek gear at even lower prices, often needing a
simple repair, once we knew where to look.

Raymond








Re: Another miserable tantalum!

Chuck Harris
 

Shhh! Don't tell anyone!

How often can you fix truly complicated looking failures
with just your eyes, nose, and an ohmmeter?

-Chuck Harris

Raymond Domp Frank wrote:

On Fri, May 1, 2020 at 07:21 AM, Dave Seiter wrote:


they would need serious derating in order to keep the failure rate down.
.... after decades.
We should be grateful for this. After all, it allowed us to acquire heaps of defective vintage Tek gear at even lower prices, often needing a simple repair, once we knew where to look.

Raymond




Re: 2465B post-recap issues.

Chuck Harris
 

U2160 is not the problem. It is a spare 2764 pad left just
in case Tektronix needed more EPROM space for some option.

The options buffer would be located in the first option board.

What options do you have?

Odds are pretty good that your GPIB card is probably not
installed properly.

DeOxit won't hurt anything. If anything it can be messy, but
electrically it is nonconductive.

-Chuck Harris

Andy Warner wrote:

I recently re-capped my 2465B and replaced the DS1225 (copied the contents
over.)

All seemed to go well, and the unit performed well in my post-rework
testing.

However, when I turn it on now, about 2 weeks later, it reports a
diagnostic failure:

TRIG'D flashes, and the following pattern is displayed:

Ready - Off
+ - Off
- - On
CH 1 - On
CH 2 - On
CH 3 - On
CH 4 - On

Reading Section 6 of the service manual, I think Tables 6-6 thru 6-8 are
telling me the problem is with U2160, Buffer ROM. Am I decoding that
correctly ?

Pressing TRIG A/B moves things along, but I am unable to see a trace for
Channel 2, all other channels seem to work correctly.

Before I clear space on the bench and tear into the unit again, I thought I
would check with the group for advice on these issues. Whether they are
likely to be connected or separate and coincidental (I don't usually
believe in coincidences.) I am not even sure what U2160 does, I need to
look that up.

I did not remove or recap the main board, it looked like a whole raft of
hassle that I did not want to get into. I did recap the PSU, A5, A9 and the
GPIB option card.

It is possible that some de-oxit got where it shouldn't have, I was
careful, but perhaps not careful enough. While I had the case open, I gave
a couple of the switches and pots a shot (including the CH2 position pot),
because they were noisy.

Regards,


Re: 496 looses the magic smoke

ArtekManuals <manuals@...>
 

Kris

I have no plans to to pry it apart

I will send you a photo of the "exploded" cap if you like

For $2 (the cost of postage) I will be happy to send YOU the cap and you can pry it apart ...8^)

Dave
manuals@artekmanuals.com

On 4/30/2020 1:01 PM, WastelandTek wrote:
Have you prised apart the remains?

RIFA cap in the potting?

--
Dave
Manuals@ArtekManuals.com
www.ArtekManuals.com
--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus


Re: Another miserable tantalum!

 

On Fri, May 1, 2020 at 07:21 AM, Dave Seiter wrote:


they would need serious derating in order to keep the failure rate down.
.... after decades.
We should be grateful for this. After all, it allowed us to acquire heaps of defective vintage Tek gear at even lower prices, often needing a simple repair, once we knew where to look.

Raymond


Re: R561B rectangular trace, I'm baffled, please help

Albert Otten
 

The rectangle probably is all there is in the display. The 561s and 564s have deflection blanking so the CRT is not cut-off during retrace. If you vary the sweep speed you might recognize which part of the loop is the actual sweep, which part is the "blanking"/retrace and which part (bright dot?) the rest position waiting for the next sweep.
The suggestion is that the horizontal deflection almost collapses when you inserted the 3A72. The vertical plates are driven directly from the plugin, so why is there veritical deflection? I suppose there was no input signal.
The plugin puts quite some load on the power lines. Did you check the power lines again while the plugin is present?

Albert


Re: Tek 5440

Tim Phillips
 

from Tim P (UK)
I've converted a few 5111s the other way (rak to bench) . The two halves
come apart reasonably easily - two low-profile bolts just by the top plugin
guides and two long-headed hex bolts at the rear. You may need a flexible
nut-driver to get to these. Then disconnect all the ribbon connectors,
noting where they all go - a mistake re-installing the 10-way connector
between the LVPS and the HV board will set all your efforts at naught.
(Don't ask !!) Don't forget the twin wire from LVPS to HV board for the
CRT. Also, with the 5440 there is a delay line which I think needs
re-routing and / or disconnecting. Not sure whether it needs unsoldering
(very thin wires) or can be moved by moving the vertical amp board.
You will also need different covers, and different spacers although you may
be able to fab something. If you have a manual, it shows how the two
variants fit mechanically.
Bon Chance !!
Tim


On Fri, 1 May 2020 at 06:05, Ron Smith via groups.io <mercedesmann=
yahoo.com@groups.io> wrote:

I bought a Tektronix 5440 on ebay recently b/c I like the big screen and I
am using it it for some audio work. I was wondering if anyone has ever
converted this upright model to a rack-mount configuration. It looks like
the modules are fairly similar to the rack-mount version. If the wire
connectors are long enough I think that is the way it will set up better on
my bench. I bought the upright model because it was in very good shape and
it was a good price, but now that I look at the way my bench is evolving it
looks like that might be better for my set up. Just wondering if anyone has
the 411 on that.




Re: 7854 ROMs: the whole story

Dan G
 

On Thu, Apr 30, 2020 at 08:27 PM, Paul wrote:

Yes please and thank you - I had assumed those were the original, unpatched
images. I have a programmer on the way, and was going to start by using the
unpatched -00 ROMS first, just to try a 'stock' configuration first.
Hi Paul,

I had also just assumed that the -01 ROM images were original as their name
implied, so I was surprised when I downloaded them, 'just in case,' to compare with
the images that I read directly from my ROMs. Since I have the -02 FPLA mapped,
I could verify with certainty that they are (correctly) pre-patched with contents
from the -02 EPROMs.

I can also confirm that the -02 EPROM images on TekWiki are correct, and
match my original EPROMs exactly.

Since you have all -00 ROMs, FPLA and EPROMs, I thought I'd look at the
wiki images for those as well. This is where things get even more interesting:
all four -00 wiki ROM images (160-0408-00, etc) are bit-for-bit identical to my
-01 ROMs!

I see two possibilities:

1) Tektronix didn't actually change the contents of the mask ROMs when they
went from -00 to -01. It is possible that they rolled the revision simply because
they changed the supplier. My -01 ROMs are made by Motorola, not MOSTEK.

2) The ROM contents *did* change, but whoever uploaded the -00 ROM images
misidentified which ROM revision they came from.

Unfortunately, I don't have any original -00 mask ROMs, so I cannot verify this
myself. However, I would really like to get to the bottom of this, as it has some
important implications:

If 1) is true, then one can simply replace a bad MOSTEK -00 ROM with a
more reliable Motorola -01 ROM (or burn a single new pin-compatible
EPROM), and be on their merry way. No need to replace all four ROMs,
kludge ROM boards, or throw away FPLAs and older EPROMs.
It would also mean that one can upgrade to version 1.03 firmware just by
replacing the FPLA and the two EPROMs with rev -02, regardless of the
revision of the mask ROMs.

2716s are readily available, or one can just reuse the existing -00 EPROMs.
It also looks like the -02 FPLA simply has additional p-terms compared to the
-00 FPLA, so one could upgrade their FPLA to rev -02 by adding in the new p-terms.
(The 82S107 is programmed one p-term at a time)

Could someone with working -00 mask ROMs and an EPROM reader please
compare their contents with the -00 wiki images? Paul, perhaps you can help with
this as well. While you probably have at least one bad ROM IC, I am hoping that not
all four of them are completely dead. Once your programmer arrives, would you be
able to read them? I would be interested in taking a look at the contents. If the
MOSTEKs are like my rev -01 ROMs, then they will be clocked, and I don't know if your
programmer will support that type of chip. Either way, if you can read them, then
this will likely identify which of your four ROMs are bad.


dan


Re: Another miserable tantalum!

Dave Seiter
 

That wasn't uncommon when Ta caps were a new technology; the manufacturers didn't recommend any derating at all, if I remember correctly.  It's the reason there are so many failures out there- no one knew they would need serious derating in order to keep the failure rate down. 
-Dave
-------
And why the choice of a 6 volt tantalum that gets up to 5 volts applied?  isn't this a little... stingy?

I will leave that half clipped-off tantalum capacitor hanging there forever, without any plans to replace it.  It is like adding a notch on my failure-hunting gun  (I don't own any guns).

Ernesto


2465B post-recap issues.

Andy Warner
 

I recently re-capped my 2465B and replaced the DS1225 (copied the contents
over.)

All seemed to go well, and the unit performed well in my post-rework
testing.

However, when I turn it on now, about 2 weeks later, it reports a
diagnostic failure:

TRIG'D flashes, and the following pattern is displayed:

Ready - Off
+ - Off
- - On
CH 1 - On
CH 2 - On
CH 3 - On
CH 4 - On

Reading Section 6 of the service manual, I think Tables 6-6 thru 6-8 are
telling me the problem is with U2160, Buffer ROM. Am I decoding that
correctly ?

Pressing TRIG A/B moves things along, but I am unable to see a trace for
Channel 2, all other channels seem to work correctly.

Before I clear space on the bench and tear into the unit again, I thought I
would check with the group for advice on these issues. Whether they are
likely to be connected or separate and coincidental (I don't usually
believe in coincidences.) I am not even sure what U2160 does, I need to
look that up.

I did not remove or recap the main board, it looked like a whole raft of
hassle that I did not want to get into. I did recap the PSU, A5, A9 and the
GPIB option card.

It is possible that some de-oxit got where it shouldn't have, I was
careful, but perhaps not careful enough. While I had the case open, I gave
a couple of the switches and pots a shot (including the CH2 position pot),
because they were noisy.

Regards,
--
Andy


Tek 555, power supply, and modules free to anyone who can come get it

abzman2000@...
 

I picked up this supply in college when they were throwing it out and I really want it to go to someone that can use it. It is non-functional, but in surprisingly good mechanical condition. I believe all of the parts are there, maybe an empty tube socket in one of the modules but not much else. It would need a complete going over, I powered it up once and the heater voltage had drifted up to the point where I shut it down and didn't want to do that again until I was sure it would calm down.

I'm in SE Michigan at the junction of I75 and I696, if you can come get it then you can have it. I'll be home all day every day and can help with loading or just leave it on my porch and you don't even have to see me let alone get within 6 feet


Re: 496 looses the magic smoke

WastelandTek
 

Have you prised apart the remains?

RIFA cap in the potting?


R561B rectangular trace, I'm baffled, please help

WastelandTek
 

Greetings TekScopers,

Dennis invited me to the group, golly, more than two years ago now and I have been watching the daily summaries go by in my email inbox but never got around to figuring out the io interface. Internet is sort of a love/hate thing for me.

I any case, to the project at hand. I have here an R561B frame, a 3B3 timebase and a number of vertical plugins.

The frame itself was filthy when I got it, and had been damp at some point, so first thing it got a pretty thorough going over. A lot of mechanical disassembly, washed everything, actually disassembled all the pots for a good cleaning. The only things I was unable to save were the scale lamps. and the switch on the back

Got it back together and it passed the smoke test and produced a trace. With the vertical bay unoccupied the timebase works properly.

However, when the vertical bay is populated things are very strange. For the time being I have been focusing on the 3A72 plugins as I have 3 of them here. After chasing out some bad tubes and wafer switch issues they all behave pretty much identically. The display is a rectangle as seen here https://imgur.com/2PfcznY if either channel is selected individually and a dot in alternate, chop, or add modes.

The vertical position knobs will move the top and bottom of the rectangle.

All the voltages in the frame look good, and I have cleaned all the mating connectors for the plugins.

Does anyone recognize this behavior?

Thanks in advance, if any group is likely to be able to help me I imagine this is the one.


Tek 5440

Ron Smith <mercedesmann@...>
 

I bought a Tektronix 5440 on ebay recently b/c I like the big screen and I am using it it for some audio work. I was wondering if anyone has ever converted this upright model to a rack-mount configuration. It looks like the modules are fairly similar to the rack-mount version. If the wire connectors are long enough I think that is the way it will set up better on my bench. I bought the upright model because it was in very good shape and it was a good price, but now that I look at the way my bench is evolving it looks like that might be better for my set up. Just wondering if anyone has the 411 on that.


Re: 496 looses the magic smoke

Chuck Harris
 

At the bottom of the message should be a link
that you can click on to unsubscribe. You might
try doing that.

The group has its email addresses wide open to the
membership, though it is now a "private" group, and
membership by invitation only.

I just removed myself.

-Chuck Harris

Greg Muir via groups.io wrote:

Chuck,

It's interesting in that, as I previously said, I cancelled my membership so cannot get back in to the old Yahoo Tek group. In addition my original setting in that group was for the digest mode only. But it seems that there have been no subsequent individual emails from that group since the short burst received earlier today.

It remains a mystery.

Greg




Another miserable tantalum!

 

Now that my 7704A is functional, I am starting to test (play) with its plugins.
I have a 7B92A dual time base that worked beautifully, except for one caveat: NO DELAY.
Everything seems correct, except that the delay time mult. pot did not multiply!
The delayed sweep always started together with the delaying sweep, no matter the position of the multiply pot.

Today I spent half the day debugging this problem in my first repairing of a 7000 plugin inserted in the scope without extender.
After studying the intricacies of the dual time base logic, I concentrated on the delaying sweep generator with its delay threshold set by the mult pot to trigger the delayed sweep.
First I suspected that the switch activated by the in/out position of the outside knob of the time/div control was defective. If always closed, this would make the threshold of the mult pot zero.
But this switch worked correctly. Then I measured the voltage on the mult pot high side, correctly around 5v. And the output of the pot would correctly change with its setting.
I measured the output of the unity gain buffer following the output of the pot, and it was strangely close to zero, not following the setting of the pot.
I tried to remove this op amp U492, a "high performance" MC1456, but strangely this one is soldered to the board, not in sockets.
The output of this op amp is followed by a resistor and then a capacitor to ground, before it is applied to the comparator that defines the end of delay..
This capacitor I initially thought as a small ceramic to filter high frequency... noise? from the op amp?
On closer observation, I recognized the pear shape and color. It turns out to be U491, a 68 uF 6v (!!) tantalum capacitor.
I measured it immediately, and it was shorted. I clipped off one end of it, and left it like that.

I immediately tried again the plugin in the scope, and the 7B92A made a perfect delay, obediently following the turning of the mult. pot.
I tested with a high frequency square wave on slower delaying sweep, then delayed to a fast sweep triggered after long delay, and I didn't notice any delay jitter. Beautiful time base!

This made me think: WHY would they place a heavy low-pass filter with a 68 uF cap at the output of a "high performance" op amp in unity gain, fed by a well regulated adjustable DC voltage?
Was this also "good practice"? Why "good"? Why not a medium size ceramic to filter out any high frequency noise, if at all, that could lead to jitter?
And why the choice of a 6 volt tantalum that gets up to 5 volts applied? isn't this a little... stingy?

I will leave that half clipped-off tantalum capacitor hanging there forever, without any plans to replace it. It is like adding a notch on my failure-hunting gun (I don't own any guns).

Ernesto


Re: 496 looses the magic smoke

Greg Muir
 

Chuck,

It's interesting in that, as I previously said, I cancelled my membership so cannot get back in to the old Yahoo Tek group. In addition my original setting in that group was for the digest mode only. But it seems that there have been no subsequent individual emails from that group since the short burst received earlier today.

It remains a mystery.

Greg


Re: 7854 ROMs: the whole story

Paul
 

Hi Dan -
Unless there are objections, I will update the wiki to make it clear
that the images are pre-patched, and add unmodified
images to the ROMs page.
Yes please and thank you - I had assumed those were the original, unpatched images. I have a programmer on the way, and was going to start by using the unpatched -00 ROMS first, just to try a 'stock' configuration first.


Re: Krohn hite UHR220

Dennis
 

Hello Hank,
Would you have a picture of the selenium rectifier area near the 5R4gy socket?? I have a UHR220 that has this missing and I need to see how things were hooked up. Previous owner did some work ???. Thanks so much and I hope you can help!

Dennis Konieczny (stook29k@hotmail.com)


TDS784D not booting, never seen this before

amirb
 

I got this TDS784D (S/N B0104XX) in an auction which could not turn on.
First it turns out that the PSU was in a startup loop and could not start, so that was an easy fix and PSU is working perfectly now.
The scope does not boot, only the front panel LEDs come on and stay with blank display. The 7SEG display on the A11 board runs through some numbers and stops at [ .8] (no flashing). I tried some of the DIP switch tests and it seemed that when I ask for FlashROM DSACK test or FlashROM Checksum test I get an error on the 7 segment LED. So I built the debug console adapter to option 13 and jumpered RTS to CTS on the RS232 port and connected a UART to USB converter directly to the MAX238 chip (pins 6 and 5). and I got the following boot log:
-------------------------------------------------------------------------
RUNNING FROM DRAM.
DRAM test passed.


Bootrom Header Checksum passed.
Bootrom Total Checksum passed.
BootRom Check Sum passed.
Bus Error Timeout test passed.

Kernel Diagnostics Complete.

Calling SDM (monitor) Routine.

Enabling Bus Control register. Value = 0x67
IMR 1 Register test passed.
Misc. Register test passed.
Timer Interrupt test (Auto-V ector) passed.
NVRam DSACK test passed.
NVRam Write protected.
Flashrom Header failed: Bad jumpcode = 0x2540001c, should be 0x4e714ef9

Flashrom DSACK-JUMP CODE test failed.
Cannot transfer control to Flashrom.
Transferring control to the SDM (monitor).
----------------------------------------------------------------------------
as I suspected from the DIP switch tests, it is failing the FlashROM DSACK tests which I have no idea what it is.
I have searched the internet for a similar error reported by others but I cannot find anybody who seen this

I dont know the history of the device, so is it possible that someone tried to update firmware and corrupted the flash rom?
or is it a hardware issue like a chip is bad on the board?

Judging by the date codes on the chips the unit must have been built around 1999 however, interestingly, the two Dallas chips have 2015 and 2016 date code on them!! and they are cleanly soldered

I am totally lost here at the moment, any help is highly appreciated.

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