Date   

Re: CRT rebuilding

 

Looking over their web page FAQ they claim to do around 50 different phosphors.I also sent them a note from there contact listing. I'm thinking at this point that cost will be the big factor.

On Sunday, March 1, 2020, 05:56:19 PM EST, John Williams <books4you@...> wrote:

Interesting. I am going to contact them. If they can redo the phosphore maybe they could change it to a different one. Depending on cost of course. Thanks.


Re: Modifications to 577 Curve Tracer Main Power Supply

 

On Sun, Mar 1, 2020 at 11:56 PM, Raymond Domp Frank wrote:


- 7 V is just about the voltage at the base of Q772 (and the slider of R775)
under normal circumstances...
... What about R776 or its connection to R775 being open..? I know you checked everything but the mystery remains...

It can't be a shorted R777, because you said that adjusting R775 does nothing. A shorted R775 would give almost - 9 V.

Raymond


Re: Modifications to 577 Curve Tracer Main Power Supply

 

On Sun, Mar 1, 2020 at 07:02 PM, Gary Robert Bosworth wrote:


This power supply does not start up correctly. The output is set at 7
Volts
- 7 V is just about the voltage at the base of Q772 (and the slider of R775) under normal circumstances...

Raymond


Re: CRT rebuilding

John Williams
 

Interesting. I am going to contact them. If they can redo the phosphore maybe they could change it to a different one. Depending on cost of course. Thanks.


CRT rebuilding

 

Just curious. I found a company that STILL does CRT rebuilding, wondering if anyone on the list has tried them or looked into it.

https://www.thomaselectronics.com/repair-overhaul/

Not sure if all they do is "rejuve" , or go as far as a full rebuild. Would be great for that aging P11

Don Frasher
AD7LL
donfrasher@...
drfrasher@...


Re: TDS2000 brightness control

Tom B
 

Unfortunately, it does not appear that there is any way to adjust the brightness.  They built the main power supply and CCFL inverter all on one board.  There is nothing to adjust.  The service manual specs the inverter output at 1400V P-P @5mA load.

I don't know if there is enough room inside to put a separate inverter for the backlight.  It might be better just to live with it the way it is.

Tom

On 3/1/2020 4:25 PM, Harvey White wrote:
You can do that, possibly.  It depends on whether or not the display has an easily replaceable CCFL bulb.

What you'd need would be an LED strip, the appropriate resistors and LEDs.  You'd need a variable PWM source or perhaps an additional resistor/variable voltage regulator to give you the brightness you want, or just adjust the resistors (which can get messy if you do it too many times).  You can adjust the resistors to work profitably on a 5 volt supply, for instance.

Another option is to replace the inverter with a variable brightness one, and put a small pot in to control that brightness.  If the existing configuration has the provisions for bright/dim the inverter, you may want to mess with that instead of putting LEDS in or replacing the inverter.

I have replaced CCFL lamps with LED strips, and do have LEDS and the blank PC boards, though.  You'll want to be able to do surface mount soldering, the parts are 1206 and 805 in size.

I'd look at messing with the control of the inverter first.  I would NOT mess with the high voltage part at all, you're talking 1600 volts at 8 ma or so to light that little CCFL lamp.

Likely the first thing would be to see what the inverter has in the way of a control voltage, for the ones I've seen, it's a simple voltage from, say, 0 to 4 volts.  Don't remember if more is less here, but that depends on the inverter.  Some are not brightness controlled, some are.


Re: Modifications to 577 Curve Tracer Main Power Supply

 

...if the -30V does not exist, then the
reference diode is never turned on.
Addition: Strictly speaking, you *are* correct, of course. It's just that the - 30 V *does* exist without the regulation part being functional - or present. In fact, the voltage would probably try to go all the way to - 40 V. The regulation circuitry (mainly VR772, Q772 and Q786) *prevents* that by limiting to - 30 V.

Raymond


Re: Modifications to 577 Curve Tracer Main Power Supply

 

On Sun, Mar 1, 2020 at 11:04 PM, Gary Robert Bosworth wrote:


The reason why I do not like this design is because of the fact that the
-30V output is used to bias the 6.2V reference diode VR772. This poses a
classic lock-up condition in that if the -30V does not exist, then the
reference diode is never turned on.
I think that's incorrect:
Whenever - 40 V is present, Q788 is pulled into conduction by R787 (to gnd), causing the output voltage to move from 0 V towards - 30 V.
The regulating circuit *reduces* that conduction by increasing conduction of Q786.

Raymond


Re: Modifications to 577 Curve Tracer Main Power Supply

Gary Robert Bosworth
 

Dennis: The parts in faded print are R773 and C773. They are not on the
circuit board.
The circuit design is not well described in the service manual. No normal
voltages and currents are mentioned in the print.
The +40V and -40V unregulated are fine.
ALL of the components measured perfectly good including the rectifier
bridges and filter capacitors.
The power supply behaves the same whether the loading connectors are
attached or not.
All of the other supply voltages are good including +200V, +12V, -12V, and
+5V.
I momentarily disconnected the short-circuit feedback diode CR785 when the
loads were not attached and it had no effect.
The reason why I do not like this design is because of the fact that the
-30V output is used to bias the 6.2V reference diode VR772. This poses a
classic lock-up condition in that if the -30V does not exist, then the
reference diode is never turned on.
I have measured every circuit trace from beginning to end and there are no
micro-cracks to open them up, and there are no solder bridges causing short
circuits.
This is a perplexing problem that I have not seen in 56 years of working in
electronics.

Gary

On Sun, Mar 1, 2020 at 11:53 AM Dennis Tillman W7PF <dennis@...>
wrote:

Hi Gary,
Which parts on which schematics are shown in shaded text?

Dennis Tillman W7pF
TekScopes Moderator



--
Gary Robert Bosworth
grbosworth@...
Tel: 310-317-2247


Re: Repairing my Tektronix 454 oscilloscope need some advice (NOW ALIVE !!)

Albert Otten
 

Good news Victor, congratulations!
I think my 454 has no net filter at all, could a filter be present in later S/N?
Albert


Re: TDS2000 brightness control

Harvey White
 

You can do that, possibly.  It depends on whether or not the display has an easily replaceable CCFL bulb.

What you'd need would be an LED strip, the appropriate resistors and LEDs.  You'd need a variable PWM source or perhaps an additional resistor/variable voltage regulator to give you the brightness you want, or just adjust the resistors (which can get messy if you do it too many times).  You can adjust the resistors to work profitably on a 5 volt supply, for instance.

Another option is to replace the inverter with a variable brightness one, and put a small pot in to control that brightness.  If the existing configuration has the provisions for bright/dim the inverter, you may want to mess with that instead of putting LEDS in or replacing the inverter.

I have replaced CCFL lamps with LED strips, and do have LEDS and the blank PC boards, though.  You'll want to be able to do surface mount soldering, the parts are 1206 and 805 in size.

I'd look at messing with the control of the inverter first.  I would NOT mess with the high voltage part at all, you're talking 1600 volts at 8 ma or so to light that little CCFL lamp.

Likely the first thing would be to see what the inverter has in the way of a control voltage, for the ones I've seen, it's a simple voltage from, say, 0 to 4 volts.  Don't remember if more is less here, but that depends on the inverter.  Some are not brightness controlled, some are.

Harvey

On 3/1/2020 4:05 PM, Tom B wrote:

Yes, that is what I got.  They do work in the TDS2000 but I think the backlight is a bit too bright.  There doesn't seem to be any way to change it short of getting rid of the CFL bulb and putting in LEDs.

Tom


On 3/1/2020 3:49 PM, satbeginner wrote:
Using Google I found this:


https://urldefense.com/v3/__https://www.goldmine-elec-products.com/prodinfo.asp?number=G19815__;!!KfGNmQmE!2zITbJD8FLS3gsRdikglcjy87OGTVu2u5BokwWCSWXYZg5hobW2T6AVS4oDo$



Re: TDS2000 brightness control

satbeginner
 

Usually these CFL inverters used for the backlight (at least in laptops) have an analog pin to adjust the brightness of the CFL, also there should be some room to play with using the contrast setting of the LCD itself.
I do not have such a device, but I changed both display and inverter in a Tektronix THS710 a long time ago having to do something similar.

Succes,

Leo


Re: TDS2000 brightness control

Tom B
 

Yes, that is what I got.  They do work in the TDS2000 but I think the backlight is a bit too bright.  There doesn't seem to be any way to change it short of getting rid of the CFL bulb and putting in LEDs.

Tom

On 3/1/2020 3:49 PM, satbeginner wrote:
Using Google I found this:


https://urldefense.com/v3/__https://www.goldmine-elec-products.com/prodinfo.asp?number=G19815__;!!KfGNmQmE!2zITbJD8FLS3gsRdikglcjy87OGTVu2u5BokwWCSWXYZg5hobW2T6AVS4oDo$


Re: Modifications to 577 Curve Tracer Main Power Supply

 

On Sun, Mar 1, 2020 at 08:53 PM, Dennis Tillman W7PF wrote:


Which parts on which schematics are shown in shaded text?
My service manual (070-1414-00) shows the main power supply on schematics sheet 11. R773 and C773 are shaded.
I made the assumption that Gary is talking about the + and - 30 V supplies, as they are the only + and - supplies in the power supply and adjustable: He mentions both + and - do not respond to adjustment (and are + and - 7V). Hence my response as I made it.

Raymond


Re: TDS2000 brightness control

satbeginner
 


Re: TDS2000 brightness control

Tom B
 

I read the manual a little closer.  The brightness command only works on the TPS2000, not TDS2000.  I guess I am out of luck.

Tom

On 3/1/2020 8:06 AM, Tom B wrote:
Hello All,

I picked up some really cheap ($3.95 at Electronics Goldmine) displays that work in the TDS2000.  The problem with it is that is looks like the backlight is too bright.  The only way that I found in the manual to control brightness is through the RS-232 or 488 ports.  Does anyone know if there is a way to control brightness from the front panel ?

If anyone is interested, the part number for the display is MTV-F32240AMNNSCW-H-1.  It was made by Microtips.  There are some on ebay, but at slightly higher prices.   I have not been able to find a datasheet on it.

Tom Bryan
N3AJA


Re: Modifications to 577 Curve Tracer Main Power Supply

 

Hi Gary,
Which parts on which schematics are shown in shaded text?

Dennis Tillman W7pF
TekScopes Moderator


Re: Modifications to 577 Curve Tracer Main Power Supply

 

On Sun, Mar 1, 2020 at 07:02 PM, Gary Robert Bosworth wrote:


The output is set at 7 Volts both plus and minus.


All of the components on the circuit board
are the correct value and are in perfect working order
Hi Gary,
I assume that you're talking about the main power supply's + and - 30 V supplies. You may not like the circuits but a few things about your unit I consider a given:
- It has worked at some stage
- It doesn't work now

If your statement that all components are ok, only wires and traces are left to consider but I've learned never to stick to any assumed certainty.

The circuit isn't the most complicated and well described in the service manual.
Before (or after) studying that, there are several simple things to consider first:

There's one thing that you should check first: Are + and - 40 V unregulated both present? Normally, they'd even be clearly above that value. If not, check rectifiers and bulk caps and their connections.

Next, disconnect the main supply from its loads. I would disconnect all, not just the + and - 30 V parts. The power supply does not get confused without a load. Any change?

The + supply needs the - supply (and +200 V) to work correctly and it mirrors the - 30 V (sign inverted) via R764. IOW, take care of the minus-supply and your problems may be gone.

You may want to check the voltage across R786. If it's anywhere near 0.7 V, the supply is in current limiting mode and your problem is downstream.

This isn't the strangest and most difficult circuit imaginable, keep a cool head and take your time to work systematically.

If no voltage makes sense, consider checking your meter...

Have fun!

Raymond


Re: Modifications to 577 Curve Tracer Main Power Supply

Gary Robert Bosworth
 

This power supply does not start up correctly. The output is set at 7
Volts both plus and minus. The variable adjustment controls have no
effect. The schematic shows several components in shaded text. There is no
explanation why these components are faded, nor is there an explanation as
to their function. All of the components on the circuit board are the
correct value and are in perfect working order. Does anyone know if the
circuit design went through any changes over the years?

On Sun, Mar 1, 2020 at 7:47 AM Lyle Bickley <lbickley@...>
wrote:

Hi Gary,

On Sat, 29 Feb 2020 15:56:03 -0800
"Gary Robert Bosworth" <grbosworth@...> wrote:

The main power supply in the 577 Curve Tracer is one of the worst I have
ever seen. Does anyone know of suggested modifications to make the power
supply behave better???
I also have a 577 - and it has always worked flawlessly. What kind of
problems
are you having?

Cheers,
Lyle




--
73 NM6Y
Bickley Consulting West Inc.
https://bickleywest.com

"Black holes are where God is dividing by zero"

--
Gary Robert Bosworth
grbosworth@...
Tel: 310-317-2247


Re: Repairing my Tektronix 454 oscilloscope need some advice (NOW ALIVE !!)

Victor
 

Albert,
Yesterday I receive from our well known friends in Greece the HV capacitor (C1460 - 500pF 20kV) suppose to be faulty. Today I install it and my 454 in now alive after 25 years sited on a shelf !
A special thank you for your help and support as well a thank you for the others members that sent several tips and comments.
Now I need to clean up some contacts and make it shine, but in the mean time I need to find a solution for the "Interference Filter" who broke down during the investigation period.
The original interference filter is a very small part and is mounted in a very thigh space. So I try to find on the market, something that could replace it, in the same place, but couldn't find any. Also I try to find information about it, since the part number show in the box is : 119-0094-03 but no information comes up. I decide to open with the idea to rebuild it, but all the parts inside are wax coated. So if somebody has any information that can help (e.g. schematic....) will be great appreciate, since the manual doesn't mention this part. I will post some photos to show the part under the name "Victor 454 interference filter".
Regards,
Victor

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