Date   

Re: need an engineers opinion

chorming tan
 

I found this article which gives a clear definition of what is ESR and the parameters that can affect its result.

https://www.sunpower-uk.com/glossary/what-is-equivalent-series-resistance-esr

ESR is frequency dependent, this means that measured value from tester that uses frequency that differ from actual application will result in ESR reading which may not be indicative of the health of the capacitor for the particular application. In the article, it says that ESR are usually specified at 120Hz and 100Khz.
However, if an application uses it at 25Khz or 1 Mhz, then expectation must be adjusted, provided a relative ESR vs freq is provided in the datasheet. So when using tester to verify the ESR using a fixed frequency, it can at most be indicative as it may be quite different on the actual application of use.


Re: need an engineers opinion

Colin Herbert
 

Could you tell us what this relates to, please? There is no quoted prior text to give us a clue.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of chorming tan
Sent: 04 December 2019 14:00
To: TekScopes@groups.io
Subject: Re: [TekScopes] need an engineers opinion

I agree. How could the measurement that applies to electrolytic not apply to other capacitors.
The principle to determine the resistance and reactance is the same regardless of the type of capacitors used.


Re: OT: floppy disk head

Michael A. Terrell
 

This was discussed in the Commodore service community in Central Florida,
about 30 years ago. I don't know if I still have any notes about it. I used
to repair Commodore computers to the component level, as a sideline. The
C64 lost a lot of RAM and ROM ICs, along with the PLA memory controller. I
saw some bad heads, but the drives were fairly new back then. I never saw a
bad head in any other Commodore series.

Used 1540/1541 drives were cheap, so very little additional research work
was done on them. I think that the only bad heads that I saw were used by a
Shareware company to make disks. Eight or more hours a day writing and
verifying copies to mail out wore out a lot of drives.

On Wed, Dec 4, 2019 at 3:13 AM snapdiode via Groups.Io <snapdiode=
yahoo.com@groups.io> wrote:

Well that's a new angle. The write current is set by a resistor for the
LM8200 chip, so either someone picked the wrong value or Mitsumi spec'd the
wrong current? I guess if it was excess current the heat would be inside
the winding so you'd never see that from the outside.
Isn't flipping a magnetic domain just a question of overcoming the BH
curve somehow and any excess signal beyond that is a waste?
Could reducing the write current on working drives extend the head's life?




Re: need an engineers opinion

chorming tan
 

I agree. How could the measurement that applies to electrolytic not apply to other capacitors.
The principle to determine the resistance and reactance is the same regardless of the type of capacitors used.


Re: 5103N Comments, advice

Harold Foster
 

Re tants: I thought that I remembered that Tek had an issue with tantalum caps from a certain period - as did Hp once they started using the solid radial variety. As i understand it, at that time the manufacturers specified that they could be operated close to their rated voltage, and as supply rail filter caps. The latter was the real killer - Tantalum capacitors can be extremely reliable when used with an understanding of their limitations, the most severe of which is current. They can accept current surges (within rated limits) and also being operated close to their voltage rating. Doing both simultaneously tends to make them into quite nice firecrackers.

Raymond: Thank you for the details - with the high cost of Tantalum's (both of purchasing one as well as having one go POP!) it is a Very Good Thing to be able to tell which need replacing and which do not. Yours was a very good - and clear - description of the differences.

Hal


Re: OT: floppy disk head

snapdiode
 

Well that's a new angle. The write current is set by a resistor for the LM8200 chip, so either someone picked the wrong value or Mitsumi spec'd the wrong current? I guess if it was excess current the heat would be inside the winding so you'd never see that from the outside.
Isn't flipping a magnetic domain just a question of overcoming the BH curve somehow and any excess signal beyond that is a waste?
Could reducing the write current on working drives extend the head's life?


Re: OT: floppy disk head

Michael A. Terrell
 

The 8050 drives were different. The bare drives for the Commodore 1540/1541
were shipped without a circuit boad. The head and motor plugged directly to
the Commodore based control & interface board. I used to repair a lot of
those drives. Mostly ones that people tried to fix by themselves. They
would play with the alignment, when the problem was bad lube in the drive
motor was slowing the disk down. Open heads were often caused by too high a
write current, in an attempt to make a longer lasting magnetic image. I had
a few good drives left, but I can't even get into that building until
repairs are made.

There were complete versions of those Neutronics drives, but I only saw
one, in over 20 years of repairing PCs. It was identical to those used by
commodore, other than having the factory board installed. I have at least a
six foo high stack of 5.25" drives, but they are in the same room in that
1200 Sq' building. :(

On Tue, Dec 3, 2019 at 7:46 PM Dave Seiter <d.seiter@...> wrote:

I wish I could help you out, because I had a pile of heat damaged 5.25"
Commodore drives years ago, but they are long gone, and were for the 8050
unit. I had a few of the actual head assemblies too, but had no idea which
drives they came from.
-Dave
On Monday, December 2, 2019, 07:21:34 PM PST, snapdiode via Groups.Io
<snapdiode=yahoo.com@groups.io> wrote:

The price for 360K or worse 170K single-sided 5.25" mechanisms is much
higher than that, I'm afraid. Besides, I am looking at specifically the
Newtronics D500 mechanism used only in the Commodore 1541 and 1541-II
drives.
You can't really just swap in another type of mechanism in there since the
front is different and it's not a PC interface.
I'm not the only one where the head failed with an open coil.
https://retrohax.net/commodore-1541-floppy-drive-fixing-chaos/

I was really looking at how the heads are built, with what materials,
specifically the potting. I'd like to see how far down I can dig into the
problem. I don't have a source of cheap PC 5.25" 360K drives either to
experiment with, and in any case I'd guess they're all slightly different
and you can't just swap in the head rail assembly across brands.






7613 on Ebay

Bruce Atwood
 

https://www.ebay.com/itm/tektronix-7613-Oscilloscope/323970848553?hash=item4b6e2ad729:g:4O0AAOSwQj9dwdRD

Looks like a good way to get a 7000 series scope so I can again use the
amazing  7A22.  I don't need the storage but gather that one can ignore
it.  Is it hard to keep running?  Other thoghts


comments?


thanks




--
Bruce Atwood PhD
Department of Astronomy
The Ohio State University
100 West 18th Ave., Room 4055
Columbus, OH 43210

Phone 614.314.0189
FAX 614.292.2928


Re: 5103N Comments, advice

 

On Wed, Dec 4, 2019 at 03:50 AM, Raymond Domp Frank wrote:


Wet slugs have the warm shine of silver, dry tants a distinctly greyish shine
- and an easily recognized hermetic seal.
I guess I should add that naturally, not all hermetically sealed cylindrical caps are dry tants. Among the notable exceptions are the big nickel-colored film caps like those used for accurate timing in time bases. Dry tants always (?) have that rain-cloud-grey semi-gloss.

Raymond


Re: 5103N Comments, advice

 

On Wed, Dec 4, 2019 at 12:07 AM, Dennis Tillman W7PF wrote:


Tantalum capacitors have a bad reputation everywhere.
That statement is a bit broad:
Epoxy-coated (dipped) tantalum capacitors and silver-cased wet tantalum capacitors ("wet slug caps") show a high failure rate *after several decades*, the dipped ones especially so when used near their spec'ed max. voltage rating.
Solid-state hermetic (glass or ceramic sealed) tantalum capacitors certainly do not have a high failure rating, on the contrary. These are among the most reliable caps available.
Wet slugs are often confused with solid-state tantalums. The former are silver-cased, use non-hermetic seals and contain sulphuric acid. Because of the non-hermeticity, they tend to leak sulphuric acid, destroying whatever is around them.
It's actually quite easy to distinguish the three varieties: the epoxy coating is obvious in their drop- or rectangular shape.
Wet slugs have the warm shine of silver, dry tants a distinctly greyish shine - and an easily recognized hermetic seal.
Tek used quite a lot of epoxy-encased tantalum capacitors from the early 1970's. At the time, it was (or seemed) a sound decision since manufacturers specified almost eternal life and no need to derate for voltage. Unfortunately, the anticipated "eternity" turned out to be 20-40 years.
HP used far fewer epoxy-dipped tants, employing mostly solid tantalums instead. Wet slugs were - and are - only used when a higher working voltage is needed than the dry varieties allow. Wet slug and hermetic tants tend to be frightfully expensive.


Contacts, switches, pots, and connector fingers will benefit from cleaning with contact cleaner, DeOxit, etc.
Almost all contact cleaners leave a more or less aggressive residue (they are used for their chemical activity after all), so especially for attenuators and other sensitive contacts, rinsing and sometimes even applying a very soft, specially formulated contact lube is advisable. In Europe, an often used three-stage procedure is employing Kontakt 60 for cleaning, Kontakt WL for rinsing and Kontakt 61 for lubing. Disclaimer: I have no shares in their manufacturer nor receive any other benefit from them; I'm just a satisfied user. Often, just rinsing with IPA or Kontakt WL is enough for (almost) non-sliding (attenuator) contacts in 'scopes, foregoing the other products.

Raymond


Re: Tek 2467B Erratic Intensity controls

Roy Thistle
 

On Sun, Dec 1, 2019 at 01:20 PM, Mlynch001 wrote:


Thanks for saying things that need to be said, but which sometimes are not
popular to hear.
Hi Michael:
Thank you! for thanking Chuck. (In my books...he's the undisputed master of valueable content penned with thermonuclear tipped butt kicking sarcasm... just like my old Elmer... no really!)
Some day we are going to miss these guys, (there's a few posting here), whose plain speaking ways were in vogue in those plain speaking days... long since evaporated away by the heat of restrictions on modern parlance.
I know I miss Elmer, whose silent key.
Best regards and wishes.
Roy


FS: Tektronix TM-5006 with AM-503, FG-503, SC-504, DM-502, and PS-503a installed.

Richard R. Pope
 

Hello all,
The TM-5006 mainframe and instruments has been sold. I appreciate everyone's interest.
GOD Bless and Thanks,
rich!

Hello all,
I am a disabled senior citizen that has a TM-5006 unit with an AM-503 Current Amp but no probe, a FG-503 Function Generator, a SC-504 80 MHz Dual Trace Scope, a DM-503 Digital Multimeter, and a PS-503A Power Supply installed in it. I am trying to simplify my life and raise enough money to be able to move back out West. I am no longer physically able to practice my electronic hobby and I need everyone's help. It would be best for some one to pick this up locally for it will be very hard for me to box it up and ship it. Please make me a reasonable offer and help a tired and old veteran out. Pictures are available on request through private email. Please respond through private email.
GOD Bless and Thanks,
Richard R. Pope
1230 19th Street #5
Reedsburg, WI 53959
608-768-7448
mechanic_2@...


Re: OT: floppy disk head

Dave Seiter
 

I wish I could help you out, because I had a pile of heat damaged 5.25" Commodore drives years ago, but they are long gone, and were for the 8050 unit.  I had a few of the actual head assemblies too, but had no idea which drives they came from. 
-Dave

On Monday, December 2, 2019, 07:21:34 PM PST, snapdiode via Groups.Io <snapdiode=yahoo.com@groups.io> wrote:

The price for 360K or worse 170K single-sided 5.25" mechanisms is much higher than that, I'm afraid. Besides, I am looking at specifically the Newtronics D500 mechanism used only in the Commodore 1541 and 1541-II drives.
You can't really just swap in another type of mechanism in there since the front is different and it's not a PC interface.
I'm not the only one where the head failed with an open coil.
https://retrohax.net/commodore-1541-floppy-drive-fixing-chaos/

I was really looking at how the heads are built, with what materials, specifically the potting. I'd like to see how far down I can dig into the problem. I don't have a source of cheap PC 5.25" 360K drives either to experiment with, and in any case I'd guess they're all slightly different and you can't just swap in the head rail assembly across brands.


Re: 5103N Comments, advice

 

Hi Hal,
Tantalum capacitors have a bad reputation everywhere. They are no more reliable in Tek equipment than in HP.
Contacts, switches, pots, and connector fingers will benefit from cleaning with contact cleaner, DeOxit, etc.
Tek wrote a two part article on spraying the scopes with deionized water (except for the power transformer) followed by an overnight warm bake. It was said to remove a lot of the residue that changes the calibration so it frequently saved time when doing a calibration.

You can find it here:
http://w140.com/Tek_Scope_Cleaning_by_C_Phillips.pdf

Dennis Tillman W7PF

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Harold Foster
Sent: Tuesday, December 03, 2019 10:08 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] 5103N Comments, advice

Yes, the manuals were acquired before the unit even arrived; both websites listed were very interesting and I'm sure that I will be referring back to them often.

I guess that what I was asking for were known issues or "gotchas" that *don't* show up in a manual - certain caps that go bad often, transistors that run hot and degrade, that sort of thing. I've been refurbishing TE (HP) for quite a while as a hobby and am familiar with the process - I just don't want to spend several hours to discover an issue that is undocumented but well known to those who have worked on this TE previously.

Thanks,

Hal




--
Dennis Tillman W7PF
TekScopes Moderator


Re: OT: floppy disk head

 

Hi SnapDiode,
My apologies. I jumped to conclusions and assumed it was a common (in there era) PC floppy disk. I don't have any advice on Commodore Floppy Disks.
Dennis Tillman W7PF

-----Original Message-----
From: snapdiode via Groups.Io
Sent: Monday, December 02, 2019 7:21 PM
Subject: Re: [TekScopes] OT: floppy disk head

The price for 360K or worse 170K single-sided 5.25" mechanisms is much higher than that, I'm afraid. Besides, I am looking at specifically the Newtronics D500 mechanism used only in the Commodore 1541 and 1541-II drives.
You can't really just swap in another type of mechanism in there since the front is different and it's not a PC interface.
I'm not the only one where the head failed with an open coil.
https://retrohax.net/commodore-1541-floppy-drive-fixing-chaos/

I was really looking at how the heads are built, with what materials, specifically the potting. I'd like to see how far down I can dig into the problem. I don't have a source of cheap PC 5.25" 360K drives either to experiment with, and in any case I'd guess they're all slightly different and you can't just swap in the head rail assembly across brands.




--
Dennis Tillman W7PF
TekScopes Moderator


TDS 5104 back up battery

matttkos@...
 

I have a TDS5104 and a service manual but it doesn't have the back up batter type info. Also, information on whether the back up voltage is needed to replace the replacement voltage during battery replacement (as some devices require). Could someone tell me the type of battery before opening the scope....thanks.

Matti T. Koskinen
DI
Avitron Co.Ky.
(OH1LWB)


Re: Power supply problem with Tek 2220

chorming tan
 

Hi Tom Miller,
I was away for 7 year and I stumble upon this question about the ESR you mentioned. I am the same guy with a different email address now.
I was thinking about it for the last few days, and I think you should be right but how to be convinced technically.
I found this link which helps
https://www.ee.co.za/article/thermal-stress-capacitors-failure-prevention.html

Let me try to show why it is so, without going through too much mathematics
It shows that ESR(heat generated) = I(rms)^2 * ESR
what is I(rms)? - this is effectively the current flowing through the ESR. if you observe the current flow through the ESR, there is a charge period and a discharge period in each ripple cycle, meaning the current changes direction in each ripple. The current ripple level is dependent on the drain current to the load. Meaning when the load current increases I(rms) ripple will increase. This is intuitive because a higher load will cause the capacitor to discharge more faster and thus will attract a charging high current in the next charging cycle to maintain equilibrium. Effectively if the load is unchanged, the I(rms) ripple is unchanged. Of course, I am assuming load resistance is greater than the ESR (RL >> ESR). In the case, when ESR approaches the load resistance, this assumption is no longer true.

For RL >> ESR
This means that power dissipated on the ESR, P(ESR)= I(rms)^2 * ESR
If load is unchanged, then I(rms)^2 is unchanged, then
P(ESR) = K*ESR, where K is a constant
This means that the power dissipated on the capacitor is directly proportional to the effective resistance of the capacitor.

This is a useful relationship, because it means that we can find a poor cap be knowing the about of heat on the capacitor.
With today's tool, we can use a thermal scanner or thermal spot scanner to check the temperature of the capacitor to determine which capacitor is bad.

Another effect if you read the link posted above, it suggest that higher temperature will cause the ESR to deteriorate. This in effect means that heat will accelerate the capacitor to its demise through the vicious cycle of Heat over time --> increase ESR --> more heat --> increase ESR further -- > more more heat -->>

rgds Tan Chor Ming


Re: 533A powering on after long storage

Roy Thistle
 

Hi Simoniep:
Great! Still among us!... please continue to be safe... a so increase one's chances of remaining among us. (Watch out for low impedance, high voltage, power supplies, in people's unfinished basements.)
Now, probably much blather follows: so read on further at the risk of impatience.
About replacing capacitors…
Well... its your scope... so if you enjoy replacing capacitors... and possibly ordering parts... then by all means... as some say here... "have fun!" (I might have added the pling… not sure.)
The 533A is not an "all American five"... so IMHO... since the 535A is working...I'd do the cal up until a problem occurs (assuming there isn't one already... and then assuming a problem does occur during cal.) … and then if it's capacitor related issue.. I'd then replace the capacitor(s) that's causing the problem.
It's not just a "if it isn't broke, don't fix it" kind of thing for me... because please believe me, I've broken lots of stuff "fixing" things, that weren't broken! There's an upside to trying to improve upon designs, and add features: you can learn a lot. (One is sort of doing that to increase reliability through recapping.) But, the downside to adding "improvements" is that it results in a lot of broken stuff... sometimes expensive stuff... if one doesn't understand the design, and doesn't have experience working with the particular technology.
Best regards and wishes.
All the best.
Roy


Re: Tek 2467B Erratic Intensity controls

peter bunge
 

-1.252
+1.367
I don't think there is a problem with the DAC

On Tue, Dec 3, 2019 at 2:37 PM Siggi <siggi@...> wrote:

On Tue, Dec 3, 2019 at 7:30 PM peter bunge <bunge.pjp@...> wrote:

I guessed that. Do you agree that the DAC Ref Adjust working means the
DAC
is OK?

The best way to verify that the DAC is working correctly is to measure
the +1.36V and -1.25V references on the A5 board. If those are good, then
the DAC and a bunch of supporting machinery is working right. If those are
way off, then you're going to have all manner of problems, as this scope is
pretty much all drive-by-wire.




Re: Tek 2467B Erratic Intensity controls

peter bunge
 

I see groups of 1.5mS, 1mS, with a 3.3ms interval.

On Tue, Dec 3, 2019 at 11:57 AM Siggi <siggi@...> wrote:

On Mon, Dec 2, 2019 at 10:31 PM Chuck Harris <cfharris@...> wrote:

Have you checked the CPU clock speed yet?
While you're in there also look at the interrupt generator counter. On my
2467 schematic it's designated U2640 on schematic <1>. This should be
generating a regular interrupt every 3.3ms, and there's a testpoint #3
where you can take a look. This interrupt is the "metronome" for the pot
scanning and DAC refreshing routines in the firmware.