Date   

Re: FG 504 problems

Colin Herbert
 

Yes, the cost was involved in my decision. The one from the US was cheaper and the postage wasn't too bad. Also, the French vendor wasn't someone I had dealt with before, so I was a bit reticent to throw a significant amount of cash at an unknown, especially considering the plethora of fakes and dodgy electronic bits that can come up on eBay from time-to-time. I thought that the US vendor was a safer bet on that account, too.
Incidentally, I am an idiot; I had a copy of the document that Stephen posted, but I didn't look it up and use it!
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 22 August 2020 15:13
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Sat, Aug 22, 2020 at 02:49 AM, <tenareze32@gmail.com> wrote:


That is a useful document, many thanks for the link.
My pleasure.

The LH0022CH is available in France and you might get it sooner from them.
https://www.ebay.fr/itm/ci-LH-0022-CH-ic-LH0022CH-pattes-dorees-de-chez-NS-boitier-TO99/201440559996?hash=item2ee6cb037c:g:KTcAAOSwU~FWDPBK
Simon
Whaoo! That’s an expensive little thing!!!


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Roger Evans
 

Luis,

It is fairly convincing that R429 is broken and responsible for the vertical deflection errors, you can check by measuring for resistance from the ends of R427 and R428 to ground. It should be a single turn trimpot so the fact that it continues to rotate is an indication that the adjuster is not moving the wiper and possibly the wiper is completely detached leaving no connection to ground.

Either way you need to find a replacement for this 250R preset that has about the right spacing of its fixing pins. Did you make a note of the position of R455 before you tried adjusting it? If so then put it back to that position as a starting point for your adjustments after replacing R429.

Regards,

Roger


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Greenpitu@...
 

Just wanted to add another observation:

If I calibrate V amplifier bias for maximum deflection (as per service manual), I no longer experience signal distortion and expansion or compression when operating the V pos dial. However the signal shown is 350mV, instead of the 300mV supposedly delivered by the onboard calibration.

I should be able to get hold of a second (and calibrated) scope in the upcoming weeks and make more accurate readings.

Regards


Re: PS503A Mod FF Photos?

Colin Herbert
 

You have a point, there. I just thought that the +5 VDC supply might give you more current to play with, which is so, but using it in a high-power bay, you have 1 A available to the 0-20 VDC supplies, rather than 400mA. I suppose someone must have thought it a good idea for the folk without a high-power bay.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 22 August 2020 15:18
To: TekScopes@groups.io
Subject: Re: [TekScopes] PS503A Mod FF Photos?

May I ask why one would need to modify a PS503A?
Can’t you adjust and fine tune the 20V supply? That’s what i do on mine... 🤷‍♂️


Re: PS503A Mod FF Photos?

Stephen
 

May I ask why one would need to modify a PS503A?
Can’t you adjust and fine tune the 20V supply? That’s what i do on mine... 🤷‍♂️


Re: FG 504 problems

Stephen
 

On Sat, Aug 22, 2020 at 02:49 AM, <tenareze32@gmail.com> wrote:


That is a useful document, many thanks for the link.
My pleasure.

The LH0022CH is available in France and you might get it sooner from them.
https://www.ebay.fr/itm/ci-LH-0022-CH-ic-LH0022CH-pattes-dorees-de-chez-NS-boitier-TO99/201440559996?hash=item2ee6cb037c:g:KTcAAOSwU~FWDPBK
Simon
Whaoo! That’s an expensive little thing!!!


Re: PS503A Mod FF Photos?

Colin Herbert
 

First off, my PS 503A doesn't have the FF Mod, but you can find text relating to the mod at http://w140.com/tekwiki/images/9/91/061-3171-00.pdf. There are no photos, I'm afraid.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jared Cabot via groups.io
Sent: 21 August 2020 02:12
To: TekScopes@groups.io
Subject: [TekScopes] PS503A Mod FF Photos?

Hi,
Does anyone have a PS503A Dual Power Supply module with the Mod FF (adjustable 5v output) installed?
I'm just looking for some photos to determine the difficulty of retrofitting this mod to my unit.


Thanks!
Jared


Re: FG 504 problems

Simon
 

That is a useful document, many thanks for the link.
The LH0022CH is available in France and you might get it sooner from them.
https://www.ebay.fr/itm/ci-LH-0022-CH-ic-LH0022CH-pattes-dorees-de-chez-NS-boitier-TO99/201440559996?hash=item2ee6cb037c:g:KTcAAOSwU~FWDPBK
Simon


Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Greenpitu@...
 

Hello!

I attempted some calibration adjustments today and as per service manual to adjust the V amplifier bias (R455) and output centering (R429).

*** Vertical Amplifier Bias ***
As in previous days, Ch1 AC div/pos 0.1V connected to onboard calibrator with 300mV square signal.

Before making any adjustments, and as per previous posts, the signal displayed is just 1/3 of the input calibrator signal i.e expands one vertical division only.

Adjusting the variable resistor R455 allowed me to increase the deflection x3. So in essence, I now was able to see the full 300mV signal, expanding across 3 divisions as expected.

If I turn the V Pos in either direction the signal no longer expands by 50%, it now compresses by approx 20%.

So I guess something still not quiet right here? Also, is this the correct way of calibrating the V amplifier? I ask because the service manual says "calibrate for maximum deflection", it doesn't say "calibrate until you see what you expect to see" which is essentially what I am doing?

** Adjust Output Centering **
No input signal, Ch1 on .2 volts/div as per manual

Connected TP322 and TP324 with DMM, and turned V Pos dial until I read 0mV on meter. At this stage, the trace was at +1.1 divisions over the center graticule line.

I then tried to adjust R429 as per manual so that trace line is exactly at the center of the graticule. But I was going nowhere! No matter how many turns I went on each direction, the trace simply didn't move, it stuck at +1.1 divisions.

Does it mean its fully open and needs replacement? Is this related somehow to the signal compression problem I mentioned above?

Many thanks and best regards
Luis


Re: FG 504 problems

Stephen
 

On Sat, Aug 22, 2020 at 01:10 AM, Colin Herbert wrote:

Interleaved.

I have no idea how you got that info, but many thanks.
I took the TEK parts number you provided and checked the reference from this document:

http://w140.com/tek_xref_free.pdf

You should download it. It will make your life a lot easier.

It wasn't available
from my usual sources like Sphere Research and Qservice.
I have now bought an LH0022CH from an eBay seller in the US. I found that the
writing around the can says LH0022CH - I was fooled by there being nothing
written on the top.
I suppose that your shops 20mins away in Paris sell these, do they?
Colin.
Since these are quite old shops, they may sometimes have some old stock stashed somewhere at the back.
But I’ve just checked; not this time.

Happy I could help.


Re: FG 504 problems

Colin Herbert
 

I have no idea how you got that info, but many thanks. It wasn't available from my usual sources like Sphere Research and Qservice.
I have now bought an LH0022CH from an eBay seller in the US. I found that the writing around the can says LH0022CH - I was fooled by there being nothing written on the top.
I suppose that your shops 20mins away in Paris sell these, do they?
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Stephen
Sent: 22 August 2020 11:39
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

Colin,
156-0484-00 is a LH0022CH, which you could replace with a more modern LF411MH/883 (same pinout), but check the data sheet, or with a TLE2141ACP and countless others (but not the same pinout).
Look here: https://www.datasheets360.com/part/detail/lh0022ch/-6869668862597770303/


Re: FG 504 problems

Stephen
 

Colin,
156-0484-00 is a LH0022CH, which you could replace with a more modern LF411MH/883 (same pinout), but check the data sheet, or with a TLE2141ACP and countless others (but not the same pinout).
Look here: https://www.datasheets360.com/part/detail/lh0022ch/-6869668862597770303/


Re: FG 504 problems

Colin Herbert
 

I am still puzzling over this. I have read the manual relating to the capacitance multiplier and have checked that C210, the resistors associated with it and switches 5, 6, 7 and 8 all look OK as far as I can tell. Also, R216 measures 10K and the slider is operating correctly (when U215 is out-of-circuit). I am left with the possibility that U215 is faulty, but I can't find a replacement. Does anyone have any better ideas, or maybe a replacement for U215 (Tektronix-made 156-0484-00)?
TIA, Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Colin Herbert via groups.io
Sent: 17 August 2020 13:53
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems


I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.
All of the power-supply voltages and ripple levels are within spec. I have got through and ensured that items #6 and #7 in the adjustment procedures are correct. These relate to the "Top Dial Waveform Symmetry (R52)" and "Minimum Dial Waveform Symmetry (R155)". The problem comes in with the next procedure "Adjust Low Dial Waveform Symmetry (R215)". This requires a 10Hz square-wave to be generated and output, but my FG 504 stops oscillating at something like 90 Hz and just gives positive pulses of approximately 3.25 ms width. This cannot be corrected with R215, which has -15 VDC on its slider, but doesn't change the voltages on pins #1 and #5 of U215. At the other end of the "Frequency Start" dial, the square-wave is more symmetrical (but not completely so) and the positive pulses are about 1.75 ms wide. This is all with the "Frequency Multiplier" switch at 10. Could this be a failure of the timing capacitor at this setting, or is R215 or U215 at fault? I have tried reseating U215 with no improvement.
The +1V/-1V triangle waveform at the junction of R225 and R228 under the conditions stated in the manual is fine.

Any suggestions as to what is going on?

TIA, Colin.


Re: 7A26 CH2 Readout

Stephen
 

After using the penetrating oil, it didn’t need to hold the front end of the BNC. After removing it, I realized there is a flat on the chassis hole, and on the plug itself, to keep it from turning, and to be inserted the right way.
It just will not move when you turn the hex nut at the back. Provided the nut is snug or just a bit tighter, it’ll turn just fine with a bit of oil. This is my first and only personal experience with removing one.


Re: 7A26 CH2 Readout

Stephen
 

In my last post, read « torque », not « torn », at the end.


Re: 7A26 CH2 Readout

Bruce Atwood
 

Use a "BNC Wrench" to hold or tighten the BNC connector. There are many different ones available or you can make your own..just a hole and a slot. Here is one that looks well made but a bit pricey. I have not used this one and I'm not associated with them.
https://www.amazon.com/BNC-Tool-Connector-Tightening-Wrench/dp/B00MEW0SCM


Re: 7A26 CH2 Readout

Jim Ford
 

Stephen and Colin, there is another way to get the BNC out. I used long-nosed pliers on the nut on the back of the BNC with just enough grip on it to keep it from turning. Then I took a rag and wrapped it around the BNC connector sticking out of the front panel so as not to mar it and grabbed the rag with regular pliers opened just enough to grip the connector without crushing it. I applied the torque to the regular pliers, and I found that they were able to grip it just tight enough to turn it and loosen the nut on the back. The space on the back is too small to get enough torque with the long-nosed pliers to break the nut loose, but it wasn't too difficult to hold the nut.

Then I did the reverse to get the BNC firmly back in place on the front panel after I did my repairs.

Hope this helps somebody.

Jim Ford

------ Original Message ------
From: "Stephen" <stephen.nabet@gmail.com>
To: TekScopes@groups.io
Sent: 8/21/2020 9:33:53 AM
Subject: Re: [TekScopes] 7A26 CH2 Readout

Thanks for the tip and offer Colin. But it’s not going to be for this repair. I messed up the BNC front end quite a bit trying to remove it. The hex screw was extremely tight and firmly stuck. Probably due to age. I had to use a lot of penetrating oil, and quite a bit of torn to get it to finally turn.
I’m just going to change it.



Re: Oscilloscope Operator Training Kit - TNGTDS01

Harvey White
 

One good source for glitches is to use a 7490 counter to drive a 1 of 10 decoder,  I think a 7442.  The decoding logic does not have a time equivalent path, and the 7490 is not synchronous.

Harvey

On 8/19/2020 1:18 PM, ebrucehunter via groups.io wrote:
Thanks Brian.

Searching online for information on the Velleman boards, I see that Jameco https://www.jameco.com/z/EDU06-Velleman-Oscilloscope-Tutor-Kit_2175568.html offers them for $29.99 .  Although inexpensive, the signals these boards generate are generally available from instruments on the bench top.  My interest in the Tektronix board is for the glitched signals it offers as a way to demonstrate the capture and storage capabilities of these DSOs for catching transient waveforms.  I have never owned a storage scope before, but on several occasions could sure have used one.

Bruce, KG6OJI





Re: Tek 465: CH1 No signal, CH2 signal reads a fraction of input, V Pos distorts signal

Greenpitu@...
 

Hello!

So I fixed the cable back to the CRT pin tube and, since I was at it, did also the other pin that was almost about to fall apart. Cleaned the area thoroughly from dust, incl. some friendly tiny spider webs.

Turned the scope back on and I am now back to square one, that is:

- Ch1 and Ch2 showing 1/3 of the input signal i.e input signal 300mV, screen display 100mV
- Signal distorts and expands on both channels when I adjust V Pos on either channel. The signal increases by 50% i.e expands from 100mV at the center of the screen to 150mV at both top and bottom ends.

I suspect I need to go through the calibrations procedure at some point, based on the details I provided yesterday?

Any suggestions regarding the size of the signal and the expanding when moving a across Y axis much appreciated!

Best regards


Re: Tek 2215 vertical gain

 

Hi,

I've fixed the issue with the traces being too low, the cause was a pair (or maybe one) of failed transistors in the vertical drive for the CRT (-) (minus) plate, on the A10 mainboard. These were Q387 (Tek 151-0127-00) which I replaced with a 2N2369A, and Q386 (BFR96) which I replaced with a BFR96S.

Here's the list of checks and measurements I made and notes on the circuit.

Following the service manual first checks were to the power supply voltages (PDF pages 75 and 176 of the manual).

Test points and voltages measured were:

TP500 -8.62V
W985 5.08V
W975 8.60V
W965 30.1V
W966 102V

So all well within spec. I set the scope controls as per the manual troubleshooting guide (so ch1 only), and measured the voltages in the vertical amplifier circuit schematic (p.159 of the PDF). This shows two very similar circuits feeding the CRT (+) and CRT (-) vertical deflection plates. The figures in parenthesis are the voltages given on the schematic, followed by actual measured voltages.

CRT + R398 (+9.0V) +9V after adjusting ch1 vertical position control pot.

CRT - R399 (+9.0V) +18V

CRT + R376 (top +2.6V bottom -4.3V) +2.0V and -5.5V

CRT - R386 (as above) +8V and -2.6V

CRT + R338 (0V) 150mV (adjusting vertical position changes from 400mV with beam highest, to -300mV beam lowest).

CRT - R348 (0V) -270mV (adjusting vertical position changes from -370mV with beam highest, to +200mV beam lowest).

The inputs to the amplifiers were at R338/R348 and the outputs to the plates are at R398/R399.

Looking at the circuit and the voltages as the ch1 vertical position pot is adjusted it became clear that the vertical deflection uses differential amplifiers, so that CRT+ voltages go positive whilst CRT- voltages go negative(and vice versa), providing noise and interference immunity, as it is the differential voltage between CRT+ and CRT- that is important, not any exact voltage of either. The beam of electrons hitting the CRT are negatively charged so when passing between the CRT+ and CRT- plates are deflected towards the most positive plate.

I checked the DC behaviour of the output amplifiers and compared CRT+ and CRT- sides. First checked CRT+ side, setting voltage at input (R338) from -100mV to +100mV (by adjusting vertical control) and measuring corresponding voltage at output (R398)

Input Output
-100mV 2.9V
-50mV 4.6V
0V 6.0V
+50mV 7.1V
+100mV 8.0V

Then did same with CRT-, input R348, output R399:

Input Output
-100mV 20V
-50mV 21V
0V 21V
+50mV 21.5V
+100mV 21.5V

Seemed very clear now the issue with the scope was in the CRT (-) side of the output amplifier, so I decided to fix it so it worked fine at DC and worry about AC later if needed. There is some coupling between the CRT - and + sides (eg the sweep separation circuit from Q370 and Q380), but nothing seemed to be amiss.

Checked a few more voltages against schematic, R378/R388 = (+30V) +30V (ok), R390 (-5.0V)
-5.3V, pressed beam find then -3.6V so ok too.

To find which part of the CRT- circuit was at fault I traced voltages through from input to output. If the voltage measured was same in CRT- and CRT+ sides then assume OK.

Again I varied the input voltage (at R338 and R348), this time only 3 values, -100mV, 0V and +100mV.

CRT- measurements(at transistor Base Emitter Collector):

R348 Q360C Q386B Q387B Q386C/Q387E R399
-100mV -0.7V -2.9V 9.9V 9.22V 20V
0V -1.7V -3.5V 9.9V 9.22V 21V
+100mV -2.7V -3.9V 9.6V 8.95V 21.5V


CRT+ measurements (* - not measured)

R338 Q350C Q376B Q377B Q376C/Q377E R398
-100mV * * -0.95V -1.5V 2.9V
0V * * 0.63V -60mV 6.0V
+100mV * * 1.6V +2.0V 8.0V

Issue appeared to be in Q386 or Q387, I couldn't tell which. First I replaced Q387, but this had no effect on the CRT- output voltages. Then I replaced Q386 and this fixed the issue. Earlier I wrote I measured R378/R379/R388/R389 as 315 ohm each (should be 340 ohm). I realised these were connected between the +30V and -8.6V power rails so I lifted the leg on one and it measured 340 ohm, so all good.

I could now move the trace from below the bottom of the CRT to above the top. I tried the front panel test square wave plus an external sine generator, and waveforms seemed fine, nice and symmetrical and no visible change when moved to top or bottom of the display. I assume when I first noticed issue with waveform peak-to-peak varying as I moved the display up and down that Q386 was on the way out, finally failed and stopped acting as a transistor.

I re-did some of my earlier measurements to wrap things up and show what typical voltages in a working 2215 scope should be. First set trace to a horizontal line exactly mid-screen.

CRT(-) R348= -64mV R389= 9.2V
CRT(+) R338= -93mV R379= 9.4V

I tested the maximum range of the vertical position control. R389 range was from +20V (trace off bottom)to -3V (trace off the top). The range for R338 was from -1V to +19V.

CRT- measurements:

R348 Q360C Q386B Q387B Q386C/Q387E R399
-100mV -1.9V -4.3V 1.7V 1.1V 7.3V Trace at +1.4 div
0V -2.5V -4.3V 4.7V 3.6V 11.9V Trace at -2.2 div
+100mV -3.1V -4.3V 6.7V 6.0V 16V Trace off bottom of CRT


CRT+ measurements:

R338 Q350C Q376B Q377B Q376C/Q377E R398
-100mV -2.0V -4.3V 2.6V 1.9V 8.8V Trace at -0.4 div
0V -2.7V -4.3V 5.4V 4.7V 14V Trace at +4.0V div (very top)
+100mV -3.6V -4.6V 7.0V 6.3V 17V Trace way off top

Interesting how much higher the CRT+ voltage measurements were following the fix to CRT- circuit, clearly a bit more coupling (eg emitters of Q376 and Q386 connected to R590) between the two sides than I anticipated.

Resulting traces on square and sine waves are now fine again, I haven't attempted any calibration but works well enough for my use.

Regards.
John

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