Date   

Re: Tektronix 475

Simon
 

I tested all the transistors in the Z-axis amplifier and all were OK. The amplifier puts out a square wave which varies from 0 to 35 V with the intensity control, but the beam was still too bright at all intensity settings. I started to suspect the voltage multiplier circuit (C1372, CR1377, CR1379) as the input was at least 40 V p-p. The components tested OK with a multimeter, but I replaced the diodes in case they were breaking down at circuit voltages. No change, but all controls operate as described in the manual with the scope probe on the cold side of C1372. The circuit diagram in my copy of the manual does not correspond exactly to the circuit description as it shows a separate winding on the HT transformer for grid bias, which I cannot locate (transformer on other side of the board). However, a 40-50kHz signal is coming through the 390 kΩ resistor (R1326) from somewhere. I will just live with a bright trace for the moment and concentrate on the Y output amplifier, which looks as thought it can be removed and tested on the bench.
Simon


Just spotted this 7854 switchable ROM (normal/diagnostic) on eBay

 

https://www.ebay.co.uk/itm/254685390375

Is this produced by one our members?

David


Re: Looking for a better in circuit ESR meter

Precaud
 

I have been successfully using an HP 4815A for in-circuit ESR testing for more than 20 years.


Re: 2465 Project, story so far.

 

OK so here is the good news update, a massive thank you to Andy Warner who sent me a new pair of ROMS, both Roms had gone, but so had U2092, I managed to get a MC68B02 for only a few UK£'s to test, and it brought it back to life (shame about the SC67127P MIL Spec Processor) but it is alive again. With the limited test kit I have calibration seems quite good, the only oddity is that channel 1 voltage measurement is about 3mv out when I check an accurate 10V reference, ( Channel 2 using the same probe and settings is spot on) Frequency on both channels is as good as I will need. I will post a working photo, and again thank you Andy.


Re: Tektronix 2230

satbeginner
 

Hi Saroj,

With respect to the voltage drop after a while, did you already removed the Molex connector from the FET?

Over the years, the FET, so also the Molex, worked at temperatures around 70 Celsius, so maybe the spring loaded contacts of the Molex are not so spring loaded anymore.... ;-)

At 1.8A about one ohm is enough to drop 2V.

Curious as always,

Leo


Re: TM500 Plug-in Extention

Stephen
 

Ok.. Since the only difference between the extender and the connector inside the mainframe is “Option 12” connected to pins 27A’s and 28A’s, I removed all the 6 coax from the back of the connectors to the 6 BNC’s at the back of the unit.

Everything behaves as expected... Baffling to me...

Now I can turn my attention to the DC505A which is counting gibberish if at all, and to the DC503 that, all of a sudden, just stopped counting altogether. Then I’ll turn my attention to the SC502 that came with the TM506.

Thinking out loud: I guess this is what you have to go through when you buy a lot of things at the same time....
A lot of troubleshooting!!
A big thank you to ALL of you for bearing with me.


Re: TM500 Plug-in Extention

Stephen
 

Worth noting though, this mainframe has Option 12 installed. But there is nothing connected to the BNC’s at the back. And all 6 of them have their leads go respectively and independently to each one of the 6 ports 28A and ground to 27A.
But there’s nothing there, and they’re not shorted.


Re: TM500 Plug-in Extention

Stephen
 

On Wed, Aug 12, 2020 at 02:32 PM, teamlarryohio wrote:


...and the Common for the variable supplies is tied to 21A, 21B, 34A, and 34B
if the schematic is accurate.
You probably mean 24A/A

Hint: The 5V ground is tied to the chassis of the PS503A. See if that is useful.
Yes, this is exactly what I have.

However, on my extender, none of these are connected. Only every pin, but 6B, from 1 to 13 are.
And, according to another post, that seems to make this unit behave “normally”...
That doesn’t make any sense...
None of this makes any sense. How can things work as intended when on the extender, but not when directly inside the mainframe? This is mind boggling....


Re: 7834 Missing Trace

Leo Potjewijd
 

On Wed, Aug 12, 2020 at 10:17 PM, Roger Evans wrote:

...
I think the C suffix means ceramic case
...
FWIW: The C stands for commercial grade, which has to do with the operating temperatures and possibly bias and offset values.


Re: 7834 Missing Trace

Roger Evans
 

On Wed, Aug 12, 2020 at 02:14 PM, <sdferg7@gmail.com> wrote:

Looking at your middle picture, it does seem that a good clean around the IC socket would be a good idea. It looks like Q555 may have been replaced and there are signs of corrosion on the surface of R570. If you get the 7A12 working well then the internals of R570 are probably OK. I would certainly pull Q555 and Q575 and give the leads and sockets some IPA.

Best regards,

Roger


Re: TM500 Plug-in Extention

teamlarryohio
 

...and the Common for the variable supplies is tied to 21A, 21B, 34A, and 34B if the schematic is accurate.


Re: TM500 Plug-in Extention

teamlarryohio
 

Hint: The 5V ground is tied to the chassis of the PS503A. See if that is useful.
-ls-


NFM - Tektronix DC503A Frequency Counter OCXO Mod

nonIonizing EMF
 

Link to the video with the gerber files linked in the description: https://www.youtube.com/watch?v=LKyo1sXVjpk


Re: DC503 Not Working

Stephen
 

This evening the DC503 that was sort of okay and counting when on the extender, just stopped counting altogether... Just showing zeros.

PS: The DC505A I received a few days ago is just randomly displaying numbers.
I must be cursed with counters... or something...

Feeling puzzled 😕


Re: TM500 Plug-in Extention

Stephen
 

On Wed, Aug 12, 2020 at 11:42 AM, EJP wrote:

That's the correct behaviour. The +/-20V posts are all floating, including the
centre one. You can't measure anything ref. ground on them. If you can in one
configuration something is badly wrong with it, i.e. one of the three is
grounded and shouldn't be.

EJP
That’s what I thought too. Otherwise why have 2 of them...?
But this correct behavior is only showing when the plugin is on the extender.
When it’s inside the mainframe, it behaves differently. Like the DC503 that is not working
when inside the mainframe, but is when on the extender... (although now it stopped counting altogether...)

This backwards behavior is insane... It drives me nuts...


Re: TM500 Plug-in Extention

EJP
 

To put It another way, if my DMM ground is in the lower (5VDC) banana plug, I can’t read anything on either +/-20VDC, and vice-versa.
That's the correct behaviour. The +/-20V posts are all floating, including the centre one. You can't measure anything ref. ground on them. If you can in one configuration something is badly wrong with it, i.e. one of the three is grounded and shouldn't be.

EJP


Re: 7834 Missing Trace

sdferg7@...
 

Ok, I will try my best with cleaning the socket. Here are some pictures of the aftermath: https://imgur.com/a/wIVfYYx

The two capacitors near it don't seem to be in the worst health so I'm not sure what caused the gunk. A kind forum member offered to mail me some spare 741s they had, so I should be able to get that sorted out. They also informed me from the pictures that mine are plastic cased. I bit the bullet and ordered a 7A26 that should be in good working condition, but it will take a while to arrive.

Shane


Re: 7834 Missing Trace

Roger Evans
 

In the UK there are a couple of eBay sellers I know I can trust and I would probably have to pay $5 for two uA741s. I have no idea which sellers in your area are reliable. You can probably get five uA741s for a couple of dollars from China but you will have to wait and once in a while you will get fake or non-working parts. They will refund your money but not your wasted time.

I think the C suffix means ceramic case, they are not normally prone to corrosion and it would be well worth while looking closely at both sides of the PCB to see if the source of the corrosion is somewhere else nearby. Electrolytic capacitors are the most likely culprit and they will need to be changed and the board given a good clean. Check that the IC socket is OK and maybe scratch around the contacts with a sharp pointed tool.

Regards,

Roger


Re: Looking for a better in circuit ESR meter

Glenn Little
 

Use any fixed with font. Courier works well.

Glenn

On 8/12/2020 11:32 AM, Roy Morgan wrote:
Chuck,

I have discovered where to change the message font in my mail program (Mail on my Mac. Mail -> Preferences->Fonts & colors).
There are about one bazillion choices of fonts.

Can you suggest one likely to work well?

Thanks much.


On May 16, 2020, at 9:42 AM, Chuck Harris <cfharris@erols.com> wrote:

If my ascii schematic isn't working it is likely because you
have your browser set to substitute your favorite font for the
font chosen by the sender.
Roy Morgan
K1LKY since 1958
k1lky68@gmail.com





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Re: 7834 Missing Trace

Dave Seiter
 

For TI, the P should be for a plastic DIP.
-Dave

On Wednesday, August 12, 2020, 10:06:19 AM PDT, sdferg7@gmail.com <sdferg7@gmail.com> wrote:

Well, unfortunately when I removed U550 and U570, I broke a leg off U570. Both are heavily corroded so I think I'll just replace both while I'm at it. The 7A12 manual lists both as replaceable by Fairchild UA741C. The closest I can find is a Texas Instruments UA741CP, not sure what difference the P makes. Would this work for my application? Any recommendations on where to purchase? Mouser.com has them for $0.50 a piece but shipping is $8.

Shane

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