Date   
Re: 7854 - yet another problem

n4buq
 

Same chip used in the TI-99/4A?

Thanks,
Barry - N4BUQ

The 7854 is based on a ti-9900 16 bit minicomputer emulating
microcomputer. Bank in the vernacular of the time, a "real time
clock" was a counter driven off of the power line. I can't think
of a reason for a 7854 to have such a clock, but I haven't studied
it extensively.

-Chuck Harris

David C. Partridge wrote:
The problem was simple once it got bad enough that I could hear the
crackle/hiss of EHT leakage - I removed the CRT (easier said than done),
thoroughly cleaned the cable and around the seal where it connected to the
PDA mesh (even though there was little if any sign of carbon tracking),
and put it back together. Since then (so far) it has behaved perfectly .

PS I think the "real time clock" problem may have been related as it hasn't
recurred. I think the real time clock refers to a problem with the "50Hz"
signal from the Readout Acquire circuit (schematic <31>). Strangely the
actual frequency in this scope was close to 70Hz (even though the timing R
& C connected to pin 6 of U2510 were pretty much spot on value).
Strangely U2510 isn't shown in the parts list for the Display Board
(A29).
It's a 155-0021-01 timing generator and swapping it with one from another
readout board made no change.

David

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of
fred@...
Sent: 05 February 2019 15:21
To: TekScopes@groups.io
Subject: Re: [TekScopes] 7854 - yet another problem

The 7854 I'm trying to resurrect has a problem where the readout starts to
flicker a lot after it has been on for a short while.

Hi David,
if you store a waveform, is it flickering as well? I had a similar problem
with the -15V supply on my 7854. It showed OK DC values by got ripple
after a short time running. It was a 330uF filter cap in the powersupply.

Re: Portable scope Tek /Sony.

EricJ
 

I'm guessing that's the one he's talking about. Neat little unit for sure.--EricSent from my Samsung Galaxy smartphone.

-------- Original message --------From: Phillip Potter <p.potter@...> Date: 2/5/19 2:12 PM (GMT-06:00) To: TekScopes@groups.io Subject: Re: [TekScopes] Portable scope Tek /Sony. I have a 335 Sony/Tektronix scope that is very portable and runs on 120 volt mains or 12v to 24v from an external battery... Awesome unit. I love mine!If not something else, you might consider looking at one.Best,PhilOn 2/5/2019 11:01 AM, vaclav_sal via Groups.Io wrote:> I like to replace my broken 464 with a small portable scope made by Tek and I believe with Sony.> About 40 years plus ago.> Do not remember the number , but it was two channel scope with attached probes , and same  hardware format as a multimeter they made.> I think it was battery operated , but not sure.>>

Re: 7854 - yet another problem

Chuck Harris
 

Same family, but likely physically bigger.

-Chuck Harris

n4buq wrote:

Same chip used in the TI-99/4A?

Thanks,
Barry - N4BUQ

The 7854 is based on a ti-9900 16 bit minicomputer emulating
microcomputer. Bank in the vernacular of the time, a "real time
clock" was a counter driven off of the power line. I can't think
of a reason for a 7854 to have such a clock, but I haven't studied
it extensively.

-Chuck Harris

Re: Portable scope Tek /Sony.

Paul Amaranth
 

The 335 does not have attached probes, you might be thinking of the 2xx series.
Look at the 212, for example. One of that series included an onscreen readout
for a DMM (the 213) Those are not Sony, however.

The Tek/Sony 335 is a bigger scope and has a higher bandwidth. I have one of those
and, except for the concentric ch1/ch2 attenuator and the AC/Gnd/DC coupling
switches, I really like it. The 336 doesn't have that problem and has digital
storage as well; that would be a nice scope.

Both of those are pretty compact and something of a challenge to fix if something
goes wrong.

Paul

On Tue, Feb 05, 2019 at 12:12:46PM -0800, Phillip Potter wrote:
I have a 335 Sony/Tektronix scope that is very portable and runs on 120 volt
mains or 12v to 24v from an external battery... Awesome unit. I love mine!

If not something else, you might consider looking at one.

Best,

Phil


On 2/5/2019 11:01 AM, vaclav_sal via Groups.Io wrote:
I like to replace my broken 464 with a small portable scope made by Tek and I believe with Sony.
About 40 years plus ago.
Do not remember the number , but it was two channel scope with attached probes , and same  hardware format as a multimeter they made.
I think it was battery operated , but not sure.




!DSPAM:5c59ee74218181533255956!
--
Paul Amaranth, GCIH | Manchester MI, USA
Aurora Group, Inc. | Security, Systems & Software
paul@... | Unix & Windows

Interested in comments on Chinese oscilloscopes

John Williams
 

Hi. This may be totally off topic and may even upset some of you. I hope not so here goes.

I am wondering if anybody has any experience with the Chinese oscilloscopes such as the Uni-T 2025 family. I am thinking of bringing one in to evaluate and compare to tektronix models of similar specs. I would be grateful if someone had experience with this type of equipment and would comment. If they are junk I would like to know or if they are useful that would be the sort of thing I would like to know. Thanks. John

Re: Inappropriate language

johnhstrauch
 

Ain't that the unfortunate truth.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dale H.
Cook
Sent: Tuesday, February 5, 2019 8:38 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Inappropriate language

At 01:07 PM 2/4/2019, Dennis Tillman wrote:

Recently a message was posted with inappropriate language that is not a
reflection of the other 7,500 members of TekScopes.

Dennis -

Thank you. Civility in public conversation is steadily coming to resemble
the dodo. It is good to see that it is still the norm in TekScopes.

Dale H. Cook, GR/HP/Tek Collector, Roanoke/Lynchburg, VA
https://plymouthcolony.net/starcity/radios/index.html

Re: Interested in comments on Chinese oscilloscopes

Harvey White
 

On Tue, 05 Feb 2019 18:39:05 -0800, you wrote:

Hi. This may be totally off topic and may even upset some of you. I hope not so here goes.

I am wondering if anybody has any experience with the Chinese oscilloscopes such as the Uni-T 2025 family. I am thinking of bringing one in to evaluate and compare to tektronix models of similar specs. I would be grateful if someone had experience with this type of equipment and would comment. If they are junk I would like to know or if they are useful that would be the sort of thing I would like to know. Thanks. John
I can summarize some of what I've heard, all second hand, and then
mention one of the little phone sized low frequency scopes.

In no particular order:

1) build quality may or may not be satisfactory
2) software support (since there's a lot of it) may be a problem
3) spare parts?
4) performance....
Now this is a conundrum. Apparently they perform well enough. How
well is something I can't say about the higher end models (I have tek
TDS and 7000 and 46x). How well built they are, resulting in a
shorter lifetime, I don't know.
5) hardware support? I have a feeling there are few schematics to be
found.
6) repairs? Considering that they are in the "mostly digital" era,
I'm not sure where we'd find the parts.

Overall opinion: They're more of a "throw-away when broken" than the
older tek equipment (I do have experience with a tek lunchbox scope,
all I could do was to replace the main power capacitor, and that
didn't fix the problem. Everything else was custom ICs and an LCD
display). The newer tek stuff is likely in that category.

Little phone sized scopes: I personally find that the user interface
is awkward, but if you want one, I'd absolutely insist on a
touchscreen interface. Three buttons or four buttons does not make a
useful interface at all. The bandwidth is quite limited, 1 Mhz or so,
which may be enough. I have a little 1 channel job with a waveform
generator output. (got it used, thankfully).

I'd rather go build something myself or go for a different (and easier
to use) tek scope.

So....

Are they worth the money?

I'd say yes, as long as you know what you're getting into, and you
want the features they have (color LCD, digital, connectivity). Comes
with the problems of being an appliance (toaster repair, anyone?).

You pays your money, and you takes your chances/choices. You may find
something used, that's tektronix, that works as well and may be more
repairable.

As a caution, the newer the equipment, the less repairable it seems to
be for (as they say) certain values of repair.....

Harvey






Re: 7854 - yet another problem

Harvey White
 

On Tue, 5 Feb 2019 16:52:07 -0500, you wrote:

Same family, but likely physically bigger.
64 pin DIL package, I think.

Wonder what would happen if you somehow managed to recode everything
for an ARM processor?

Harvey


-Chuck Harris

n4buq wrote:
Same chip used in the TI-99/4A?

Thanks,
Barry - N4BUQ

The 7854 is based on a ti-9900 16 bit minicomputer emulating
microcomputer. Bank in the vernacular of the time, a "real time
clock" was a counter driven off of the power line. I can't think
of a reason for a 7854 to have such a clock, but I haven't studied
it extensively.

-Chuck Harris

Re: 7854 - yet another problem

Chuck Harris
 

Nirvana.

I have an adapter CPU card for just such a venture. A guy
named John Seamons, of timenuts fame, designed an interface
board between a Beagle Bone Black/Green single board computer
and the HP5370A/B frequency counter. A BBB/G SBC plugs directly
into his board, and the interface board plugs directly into the
CPU's slot in the 5370A/B motherboard. The BBB/G SBC runs the
original 6802 firmware using a linux hosted 6802 emulator.

The BBB/G SBC also runs a SSH server that allows you to communicate
directly with the 5370 counter, does enhanced software
processing of the counter's data (Allen Variance, printing,
plotting..., and provides both ethernet and USB interconnectivity.

Faster, lower power, more features...

Nirvana.

-Chuck Harris

Harvey White wrote:

On Tue, 5 Feb 2019 16:52:07 -0500, you wrote:

Same family, but likely physically bigger.
64 pin DIL package, I think.

Wonder what would happen if you somehow managed to recode everything
for an ARM processor?

Harvey

OT: wanted -- HP 8340 Or HP 8341 Sig Gen non-working parts unit

garp66
 

hi,
I need an HP 8340 Or HP 8341 Sig Gen non-working parts unit to repair my unit (multiple issues).

A non-working, but complete 8340 Or 8341 would be good.

Please contact me off-list,
thank you,
rick

Re: 7854 - yet another problem

Harvey White
 

On Wed, 6 Feb 2019 08:10:38 -0500, you wrote:

Nirvana.

I have an adapter CPU card for just such a venture. A guy
named John Seamons, of timenuts fame, designed an interface
board between a Beagle Bone Black/Green single board computer
and the HP5370A/B frequency counter. A BBB/G SBC plugs directly
into his board, and the interface board plugs directly into the
CPU's slot in the 5370A/B motherboard. The BBB/G SBC runs the
original 6802 firmware using a linux hosted 6802 emulator.

The BBB/G SBC also runs a SSH server that allows you to communicate
directly with the 5370 counter, does enhanced software
processing of the counter's data (Allen Variance, printing,
plotting..., and provides both ethernet and USB interconnectivity.

Faster, lower power, more features...
Let you know when I get the DM5110 done like that. Front panel
readouts work, sooner or later switching and instrument interface.

ST micro F446 processor on their Nucleo 64 board, FPGA for front
panel, and one of two 488 bus chips on an add-on board.

I *could* write an emulator that would run the original code from the
ROM dump, but the possibility of programming in C (rather than 6802
assembly), adding an OLED readout behind the front bezel, and adding
more functions (such as a built in cal routine), well....

no assembly...

Another option would be to take the CPU board, add a readout, use a
488 controller, add a wifi module running MQTT, and then having a bit
of fun with that. Separate case, of course.

Harvey


Nirvana.

-Chuck Harris

Harvey White wrote:
On Tue, 5 Feb 2019 16:52:07 -0500, you wrote:

Same family, but likely physically bigger.
64 pin DIL package, I think.

Wonder what would happen if you somehow managed to recode everything
for an ARM processor?

Harvey

Schematic and component for 7834 A16 LV regulator board 670-3665-03

 

I'm working on a 7834 power supply that's a ticker.

The board layout for the LV regulator differs from that shown in the manual
and I suspect that the schematic may also be different.

The manual I'm using is 070-1988-00 revision date December 1984. The
electrical parts list acknowledges that this level of the A16 board exists,
but doesn't seem to have a parts layout or revised schematic.

Is there a version of the manual that does cover this?

Thanks
David

Re: Interested in comments on Chinese oscilloscopes

Michael
 

I have 4 Tek scopes. Two are 465s. I also have a Hantek lunchbox scope. It is 2 channel 200 mhz. When I work on simple stuff like stereos and HF transceivers, the Hantek has a unique advantage. It will tell you everything about the signal on a readout to the right of the signal picture. I know the DC level, frequency,amplitude, and time period. I simply hook up my probe and push the automatic acquire button. Everything is displayed in front of me. Now the bad news. I am sure this scope is not repairable. I paid only 300 dollars for it and figured that going in. It does not have enough dots on the display to show a square wave without a little jump on the downward or upward excursion. This problem is not a real problem but one of aesthetics. When I want to do something that is more serious than simple radios or stereos, I use a 465. I like the smooth crisp trace. It reacts to signal changes in real time. There is a very slight delay in the Hantek, Probably all that processing going on. If I had to only have one scope, it would be a Tek 465. This is even though most of my repairs are done with the Hantek. I also know that it is most likely that I can repair a problem with the Tek scope. I have already done so. A large electrolytic capacitor shorted in one of the power supplies. Very easily fixed. Time will tell how long my Hantek will run. I did complain to the reseller about a problem with the Hantek after I just bought it. It could not respond and show an SSB signal output from a transmitter. It would just show a bunch of hash because the processor got confused. That reseller, bless his heart, sent me a firmware update that fixed this. I can now see what the SSB output signal looks like. I was fortunate enough to afford buying old Tek scopes and a Hantek. I believe they each have their place on my workbench. Here is a picture of my workbench:
http://www.ironwoodelectronicsrepair.com/

Re: 7A26 attenuator compensation problem

Nenad Filipovic
 

Hi Fabio,

I do own a 7A26 myself and 10 and 20mV ARE NOT the ranges where all the
high impedance attenuators are BYPASSED.
My mistake while writing my own post in haste, sorry, of course the 5mV and
10mV are the bypass ranges.

My 7A26 is serial B226210, which means it's a later model that has the 3rd
implementation (revision) of the JFET input buffer (can find it in the 1983
and 1986 instruction manuals). My issue is most certainly in the area of
attenuator blocks and the JFET buffer, as I can see the aberration if I
look at the buffer output using another scope. And everything is cleaned so
no lousy contacts, DC noise...etc.

Regarding your calibration procedure I agree, not sure though whether it is
really necessary to switch from 50ohm to 1M normalize every time. Either
way I indeed manage to calibrate everything properly, at least in the
frequency range that the adjustments have effect on. In more detail -
compensation can be best observed using square wave signals in the
1kHz-5kHz range. If I set it right at these frequencies, I get the
aberration seen on the photos I posted od 100kHz. I currently have it set
as a compromise between 1kHz, 10kHz and 100kHz, but I'm not happy with it.

The area of attenuator blocks and JFET buffer is *very* sensitive to stray
capacitance, e.g. if you touch the attenuator blocks with your fingers, the
response in the problematic range (10-100kHz) changes substantially. In
another words, just a few pF means a lot to the response, at one point I
managed to get the 500mV (the most problematic setting) perfect just by
holding my finger in the right place. This lead me to believe that there
may be a certain value of C130 and C134 at which everything "fits", so I
increased C130/C134 and re-calibrated everything again just to find out
that if I make the 500mV perfect by looking at the 100kHz square, then
10kHz is no longer good. Again the conventional calibration (trimmers in
the attenuator blocks) act on lower frequencies (best seen in ~1kHz-5kHz
range) than where the problem appears afterwards (~10kHz-100kHz range). A
home made normalizer can be used to set all the inputs to the same
capacitance, but cannot really tell you whether you are exactly at 22pF.
For this reason the C130 adjustment from the service manual is pointless,
as you can set it to any value and match it using normalizer adjustment.
But question remains how far you can safely deviate from 22pF and still be
able to compensate all attenuator blocks.

Just to add to the confusion, those nasty carbon composite resistors next
to attenuator blocks have all drifted +10% to +20% in value, but replacing
them did not make any change. I suppose these come into play on very high
frequencies (>100Mhz), as another group post has demonstrated:
https://groups.io/g/TekScopes/topic/19243444

Perhaps some other component has drifted in value, e.g. in the JFET buffer.
Unfortunately I do not have another 7A26 to swap parts, but in a few months
I may get another one that is sitting at a friend in US and waiting for
someone to carry it over the ocean.

Best Regards,
Nenad FIlipovic

Re: Interested in comments on Chinese oscilloscopes

John Williams
 

Many thanks to both you and Harvey for your information. I also have a 475A and find it very useful. I took a look at your website and found it very refreshing to look at after my messy shop.

I don’t know that I would actually use a “lunchbox “ scope or not. I would purchase one more to see what some of the new stuff is like. I have looked at some of the sellers feedback and was not impressed by some of what I read. For working on plugins which is what I do mostly now I use the 551 setup, lower to connect the plugin and upper to trace through it. For working on scopes I use the 475 or 2213.

Still these lunchbox scopes interest me and I might just pick one up for fun. They say you can’t have enough love, money, or scopes. So one out of three is not bad, right?

Re: Interested in comments on Chinese oscilloscopes

Siggi
 

Hey John,

the EEVBlog has discussions and reviews of B-brand scopes ad nauseum.
There's even a comparison spreadsheet that looks to be reasonably
maintained in a sticky thread <
https://www.eevblog.com/forum/testgear/digital-oscilloscope-comparison-chart/>.
Looks like the Rigols and Siglents are best of the rest there, you may want
to look-see before you make your purchase. Micsig is another brand that may
warrant a look, as those are tablet-like scopes with a touch screen and a
fairly unconventional form factor.
Even for the best-of-the rest, however, there have been some worrisome
problems, like there was a Siglent scope that would significantly change
input capacitance between input ranges. This would require you to
re-compensate the probe anytime you switched across some threshold...

Of these scopes, I've only ever used a Rigol 2000-series myself, and it's
... not awful. I would get used to it as a daily driver, I figure, if I had
to.
I still prefer my 2467 for usability any day of the week, and when I need
to observe slow or single-occurrence things I go to my HP 54622D. That one
still doesn't have any protocol decoding, which is the one feature I'd love
to have in one of my scopes...

Siggi

On Wed, Feb 6, 2019 at 5:52 PM John Williams <books4you@...> wrote:

Many thanks to both you and Harvey for your information. I also have a
475A and find it very useful. I took a look at your website and found it
very refreshing to look at after my messy shop.

I don’t know that I would actually use a “lunchbox “ scope or not. I would
purchase one more to see what some of the new stuff is like. I have looked
at some of the sellers feedback and was not impressed by some of what I
read. For working on plugins which is what I do mostly now I use the 551
setup, lower to connect the plugin and upper to trace through it. For
working on scopes I use the 475 or 2213.

Still these lunchbox scopes interest me and I might just pick one up for
fun. They say you can’t have enough love, money, or scopes. So one out of
three is not bad, right?



Re: Interested in comments on Chinese oscilloscopes

nonIonizing EMF
 

On Wed, Feb 6, 2019 at 02:52 PM, John Williams wrote:


Still these lunchbox scopes interest me and I might just pick one up for fun.
I thought the NI Virtual Bench system seemed like the ultimate if I could find at a great price mobile bench. Pipe dream. I did however, pick up an NI ELVIS system for ~$20 and am seeing them for around $50 on eBay at the moment. You'll need a DAQ and I happened to find PCMCIA 6024E in a $10 IBM T42 laptop at the UofM Property Disposition Store. The DAQ will limit the capabilities of the Oscilloscope sample rate and bandwidth, so really for the price the cheap Chinese systems seem the way to go other than having an educational and prototyping breadboard with components all in one system that is more American. I found a 68pin cable also for $5 and wound up investing maybe another ~$100 in another cable and an FPGA prototype board. If can find a deal on an NI ELVIS2... then those are USB direct interfaced. The boards plugs are a PCI plug also... so seems easy to have a custom board made if wanted. Seems interesting and versatile if have a computer at your workbench and at the time I thought would be handy for at a remote station as well as an educational system. Other than that... I've been looking into the smaller cheap DSO scopes and RF modules to try to put together a mini/micro field kit.

Originally, I was looking at the DSO138 as a good kit to practice soldering the not yet SMD components. Then I see now there are the DSO224 at unbelievable prices for the performance... though is almost like with soldering that small... need a magnifying glass to read the screen. :-) Figured one of those or an SDR and a DDS frequency generator would be an easy to port around mobile kit with a TS100 soldering iron, a LCR-T4 meter and what I bought as a Sepic Cuk power supply is called a "DIY USB Boost Single Turn Dual Module Linear Regulator Multiple Output Power Kit" on eBay now. Thinking can be ran from the custom Dewalt 20V adapter from a 20V tool assembly I recently worked on identifying the wires to make a hacked together 20V to 18V adapter from a 20V Dewalt tool trigger assembly. There's always the sound card on the laptop method too for the lower frequency work. Virtual Analyzer software and the latest TAPR caught my eye recently and I just ordered modules to build. https://github.com/erikkaashoek/Tapr-VNA

There are oscilloscope plugins for the SDR's... so that was where I last settled on. I ordered a set of attenuators also and some other components. Thinking I need a current limiting circuit in between also so I don't overload the SDR just in case.

For now... if not a sound card SB1095 or SDR interface to the laptop... I'm still planning on modifying one the of the TDS-520's to run off batteries for in the mobile rig. The bandwidth is impressive... however... would be nice to be able to re-code the firmware to have more FFT options and display options more like the modern configurable displays. Hard to beat that performance for price and I'm still to nervous to use the TDS-744A and hack into a TDS-784A. I still need to play around with the 7904 different modules and 475A and boost my confidence. For mobile work though... those little DSO things are looking better every time I look. Wondering how those compare in performance with the Uni-T 2025 in the equivalent spec ranges?

Orlando Hamfest

Harvey White
 

I'm going. It's this weekend, Friday 9-5, Saturday 9-5 (biggest day),
and Sunday 9-2.

I'll be there, likely on Friday and Saturday. Not sure about Sunday,
depends on Saturday and whether or not I've gotten all that I want.
(as always).

Please contact me off list (you have permission) to get contact
information. It would be nice to meet up a bit. Depending on the day
(and what's there) I am generally there at 9 AM, but may leave before
noon (Friday?) and 2 (Saturday) and may not be there Sunday.

Harvey

Rickreall OR Hamfest

 

The Rickreall Oregon hamfest is in 10 days on Feb 16.

I will be there and I will have a table with Tek stuff on it.

If you are going come and find me. The folks at the door can tell you which
table I'm at and where in the hall it is located. I'm usually along a wall
since I requested a table with power.

Dennis Tillman W7PF

Re: Rickreall OR Hamfest

Harvey White
 

On Wed, 6 Feb 2019 18:02:40 -0800, you wrote:

The Rickreall Oregon hamfest is in 10 days on Feb 16.

I will be there and I will have a table with Tek stuff on it.

If you are going come and find me. The folks at the door can tell you which
table I'm at and where in the hall it is located. I'm usually along a wall
since I requested a table with power.
I think I'll pass on this one. You do realize how far Florida is from
Oregon?

Thanks for the invite, though.... <grin>

Go up to Sphere and get some goodies....


Harvey



Dennis Tillman W7PF