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Re: Packaging 7854 scope for shipment?

David Holland
 

As a somewhat off topic example of how *not* to pack....

https://photos.app.goo.gl/PscEindwAHv71JqH9

Step 1) Do not go to the local U-HAUL place, and pick up a short wardrobe box.
Step 2) Do not fill 1/2 way with peanuts.
Step 3) Do not place large heavy device on peanuts.
Step 4) Do not fill remainder with peanuts.
Step 5) Do not ship in this condition.

Its a RM567. Surprisingly it appears to have survived the journey
(AZ to OH - via Fedex)

To keep it OT: Agreed, the foam/foam in place & double boxing are the
general recommended methods for shipping large heavy boxes. That
being said, I can see where that might be somewhat difficult to do
with a 7854, and is starting to sound like freight.

FWIW, I've also heard (via the antique radio guys) that Greyhound is
not a bad way to ship large heavy things and they may not receive as
much abuse as they would via the regular shippers.

David

On Mon, May 27, 2019 at 6:16 PM John Griessen <john@...> wrote:

On 5/25/19 10:19 PM, Dennis Tillman W7PF wrote:
Have you eve received anything that was packed with "Foam in Place". It is simple and quite robust.
That foam is really a good density and yieldingness, and carves easily. I reuse big chunks of it to pack things
by carving it with a long serrated knife, (usually for bread).


Re: Weird(?) behaviour in tek 492BP power distribution - Please help

Harvey White
 

I don't know this (and don't have one) particular instrument. All I can do is to give you some general pointers.

Many power supply designs depend on a particular supply to be exact.  Generally you'd expect a zener or a reference to point out what voltage the supply *should* be.

ANY drain on that supply that would cause it to shut down due to overload, or not supply enough current to achieve the proper voltage will throw every other power supply off, if those supplies use "the supply" for a reference.

If that reference supply is ok, then look at each individual supply to see if those are at the proper voltage.  Too much current on any supply can cause it to fold back or drop out of regulation, however, if it's not the reference supply, then look at that supply only.

Typically, supply problems start with (and are not in order of probability, but are working from the line to the equipment):

1) bulk supply errors, the transformer/switcher etc does not give you the right supply voltages.  Generally things like bulk capacitors and bridges in linear supplies, gets more complicated in switching supplies.

2) reference supply errors (see above).

3) individual supply errors.

Many individual supply errors are caused by too much current drawn.  Other than bad semiconductors (less frequent than perhaps thought), your main problem is likely to be extremely leaky or dead shorted tantalum capacitors.

Sometimes bad supply voltages are caused by bad resistors in voltage dividers, or bad transistors.  Perhaps less frequent than you think.  Depends on the individual piece of equipment.

All this does ignore any other faults such as solder splashes, broken wires, etc.


Harvey

On 5/27/2019 3:39 PM, Roger via Groups.Io wrote:
Dear all,
I bought one of those beasts at a reasonable price and it arrived in a very good overall condition.
The trace was crispy and I could see the peaks of the calibration signal.
Then I realized the the center frequency/marker button was not working and I disassembled the front panel to find the cause.
Later I learned the it was only a burnt mini lamp that was replaced and the front panel was reassembled.
When I turned the instrument on again, there was a flick and no trace was visible.
I checked the voltage test points on the Z-axis board and the +100V was gone and the +300V was low.
So I disassembled the Power Supply Module and checked the caps, and noticed the 100V (F-1035) was burnt.
Following the advice given by John Miles in his notes, I replaced the caps in the +100V and +300V supplies and measured all voltages (with the power module disconnected) and they were all good.
Since there was a blown fuse I checked for shorts on the Z-axis board, deflection boars and the HV board.
The only problem I could find was a shorted Q1073 oscillator transistor that was replaced by a NEC C2333.
Reassembled the board, turned the instrument on and to my surprise, NO TRACE.
Checked the voltages again on the Z-axis board and the +300V dropped to +245V and +100V raised to +145V. Is this normal?
Also, there was no Hi Voltage in any of the terminals of P742,!!!
I bought an HV board from Ebay and a set of extension boards from Norway Labs.
While these items are on their way, I decided to measure the voltages on the male header of the motherboard (just in case...).
To my surprise none of the values make sense!!!
The +15V, and the -15V were totally off, the +100V was +85V and I am not sure the exact value of the +200V.
My Z-axis board has the power status indicator led that is green, and all test points measure ok?
Also, I could not find a diagram with the pinout of my motherboard (12 pin header, one pin not installed)
Are there any components on the power supply rails of the motherboard?
I could not find any reference to them.
Any suggestion would be greatly appreciated.




DC voltage on a DC coupled spectrum analyzer

DW
 

I am well aware that a DC coupled spectrum analyzer might take up to +30dB peak but no more than 0V DC. The slightest DC voltage can destroy a DC coupled spectrum analyzer.

Curious if anyone has any thoughts about what goes on inside a DC coupled spectrum analyzer where if a DC voltage is applied why damage occurs. Thanks.

Re: DC voltage on a DC coupled spectrum analyzer

DW
 

https://www.edaboard.com/showthread.php?196119-Why-DC-be-not-given-input-to-a-spectrum-analyser

Here is what I found if anyone is interested. It seems when you apply a DC voltage the mixer consists of diodes and when you apply enough forward bias to it, it will turn on and supposedly current increases exponentially damaging the mixer.

Re: 2246 no display/odd behavior

Matt
 

Thanks. I will start with replacing these. They did all test fine in circuit but I understand that doesn't mean much for these particular diodes.

One question on this main board: do most people remove it to work on it or just solder from the top side? Looks like quite a pain to remove but, then again, soldering on the top is not fun either.

Lastly, errata from my previous marked up schematic: on the far right "+42 to +42" should be red, not green.

Re: Packaging 7854 scope for shipment?

Brad Thompson
 

David Holland wrote on 5/27/2019 7:16 PM:

As a somewhat off topic example of how *not* to pack....
<Gory details snipped>

Hello, David and the group--

My thanks go to all who responded, and I hope that all of the good advice
reaches the archives to help future shippers.

Before I proceed any further, I'll prepare a description of this 7854 and its
condition. I'm located in western NH and I may offer it FS/local pickup as
a first resort (although this area isn't exactly a hotbed of interest in electronics).

Thanks again to all, and 73--

Brad  AA1IP

Re: Weird(?) behaviour in tek 492BP power distribution - Please help

radioconnection@...
 

I don't see how loading down the 300 VDC supply to 245 would in anyway increase the 100 volt supply by 45 volts. I think you'd better look for an unwanted leakage path between the 100 and 300 volt supply. Check the power supply board carefully for a wiring error, solder bridge, etc. or a cap that was installed backwards, esp. those used on the 300 volt tripler.

Pete

Re: DC voltage on a DC coupled spectrum analyzer

Ed Breya
 

DC is just 0 Hz - there's no need to worry about the DC level if it's within the power input rating. If an SA is rated for operation to 0 Hz (DC-coupled), then it is typically for a wide bandwidth including 0 Hz, or at least to very low frequencies, and no coupling capacitor (or transformer) is used, which would limit the low-end response. Also remember, this assumes a 50 ohm or whatever source resistance - it's the current that can blow the input mixer if too much voltage is applied from too little source resistance.

The main reasons for specifying that no DC is allowed, are because DC offset on the input may upset the mixer balance, causing errors in the conversion process, and that excessive DC may be inadvertently applied due to operator error or measurement failure. SAs are typically for looking at AC/RF signals - that's where the information is - not particular DC levels, unless the information is at very low frequencies. Is 1 Hz approximately DC? How about 1 mHz? It depends on the application.

A common risk to SAs is in probing around an RF circuit, say an amplifier, which has DC levels present, for operation. An operator error like hooking up to an RF node that has significant DC available, without assuring that it's either AC-coupled, or that the source resistance is high enough to limit fault currents, can damage the SA. The safest approach and rule of thumb and specification is to not allow any DC at the input. If you don't heed this advice, then it's your own fault. In reality, some DC is no sweat, but it's best to just say zero.

Ed

Tektronix 4205 Display Terminal

Gary Robert Bosworth
 

Does anyone know if the processor board located in the bottom of the 4205 CRT Display easily slides out through the rear? Also, are the ROMs located on this processor circuit board? Unfortunately, the 4205 is radically different from the 4105 in its physical layout. I am unable to locate service manuals for the 4205 Display monitor.

Looking for replacement case for TDS303X

 

I recently purchased a TDS3034 with a case that is in worse condition than anticipated: The rims on the feet assemblies and the rear cover are damaged, the front part is OK.
I've decided to start looking for another 'scope with identical applicable case parts and in very good state.
Does anyone know which models' cases are compatible? I guess all non-suffix TDS303X'es but any others?
If any member of this group has a cheap/low spec. or defective unit that' they'd sell, please let me know, preferably in Europe since I'm in the Netherlands.

Raymond

Re: Weird(?) behaviour in tek 492BP power distribution - Please help

 

I agree with you, and that's why I feel helpless about this situation.
All voltages measured ok after I replaced those caps and the power supply was disconnected from the equipment..

Re: 2246 no display/odd behavior

chipbee40
 

For transistors and 2 leg components etc definitely work from the component side. way too much trouble otherwise. Cutting leads may be a good idea before pulling or maybe tacking to existing leads.

Re: Weird(?) behaviour in tek 492BP power distribution - Please help

radioconnection@...
 

Can the supply be run while removed and disconnected from the analyzer? A cap could have failed after being installed and used for a few minutes. I'd wonder what the voltages are without the instrument being involved.

Re: DC voltage on a DC coupled spectrum analyzer

DW
 

Great answer, thanks

Re: Looking for replacement case for TDS303X

 

On Tue, May 28, 2019 at 11:30 AM, Raymond Domp Frank wrote:


I guess all non-suffix TDS303X'es but any others?
Most obvious when compared to letter scopes:

B has:
Parallel port
DC OUT on different location
Cal switch and GND terminal are the same
Ethernet port
EXT Trig connector on 4 CH scopes

C has:
No Parallel port
No DC OUT
Cal switch and GND terminal are the same
Ethernet port
EXT Trig connector on 4 CH scopes

There may be some internal changes too so the safest option is to look for a no letter donor.

/Håkan

Re: DC voltage on a DC coupled spectrum analyzer

radioconnection@...
 

Unless you have a need to go into the LF region, a DC blocking accessory is cheap insurance.

Re: DC voltage on a DC coupled spectrum analyzer

Chuck Harris
 

Often, a DC block isn't insurance at all.

Every DC block I have met is simply a series capacitor, usually
about 0.1uf... those for lower frequency SA's, can be several uf,
so as to not degrade the low frequency performance too much.

If you suddenly apply a high DC voltage, from a low impedance
source to the DC block, it will apply all of the charging current
impulse directly to the SA's front end. This impulse can quite
easily destroy the mixer, if it is directly exposed without an
attenuator.

Best is to be cognizant of what you are doing, and discharge long
coax runs, and antennas, before connecting, and simply don't connect
any DC charged source to the SA without using using a high
impedance probe... preferably with a series capacitor.... 10M scope
probes are often a very good choice for probing in dodgy situations.

-Chuck Harris

radioconnection@... wrote:

Unless you have a need to go into the LF region, a DC blocking accessory is cheap insurance.



Re: Tektronix 4205 Display Terminal

Dave Wise
 

I worked on the 420x firmware. I don't remember the mechanical details except that the connector for the Option CX board (which I did) is not on the bottom at all; Option CX is vertically mounted in back, with a right-angle connector to another vertical board that's on the left or right side when viewed from the front. So that board might be the processor board; at least it contains address and data buses. I think the board on the bottom is actually the monitor. I could be wrong, it's been 30 years since I gave it a thought.

Tek was OEM-ing some monitor hardware around that time; they may not have had the info themselves.

HTH,
Dave Wise
________________________________________
From: TekScopes@groups.io <TekScopes@groups.io> on behalf of Gary Robert Bosworth <@grbosworth>
Sent: Monday, May 27, 2019 11:10 PM
To: TekScopes@groups.io
Subject: [TekScopes] Tektronix 4205 Display Terminal

Does anyone know if the processor board located in the bottom of the 4205 CRT Display easily slides out through the rear? Also, are the ROMs located on this processor circuit board? Unfortunately, the 4205 is radically different from the 4105 in its physical layout. I am unable to locate service manuals for the 4205 Display monitor.

Re: DC voltage on a DC coupled spectrum analyzer

DW
 

Here is a thought, for example a HP 8566 which can go down to 100 Hz. I assume they choose that number as that is the lowest it can go for certified performance, but I wonder if they choose that number could also be the minimum safe frequency range. For example if you go below the 100 Hz minimum to say 60 or 30 Hz, or maybe even 10 Hz, I wonder if that presents a hazard to the mixer as there is a longer but brief duration of positive and negative DC without a DC blocking capacitor that could cause eventual damage.

2215 problem

Bob Albert
 

My 2215 stopped working. At first I thought it was the power switch but that isn't the case.

The manual shows an inductor off the power circuit board but mine doesn't have that. It has an FET instead. There is a pair of wires going from one board to the other. I apparently don't have the correct diagram for my unit. Would it be safe to short the two leads to get the unit working? Would that provide a path for the power?

This is a sophisticated power supply. No voltage is reaching the switching circuit. The FET I mentioned is on a sort of heat sink in a little plastic box. I lifted the part to read its designation (IRF820) and one lead promtly broke. I have in my stock an IRF740 that appears to be close enough.

Anyway I am uncertain how to proceed. All help appreciated.

Bob