Mac

Hello everyone,
This post is a follow up from post #7360, and my 7L13 with center frequency LED readout all zeros. I am a bit further along with my investigation. I now understand the operation 'somewhat' more. I have looked over the diagrams and taken some voltage readings, I also understand the basic DVM logic and readout operation which sends data to the LCD and the CRT. I have an article from a Jan, 1975 '73' magazine which talks about the Fairchild 3814 digital voltmeter. I must admit I am not too clear on the 'Analog' section of the meter. On board 'A2100', diagram 12, the input to pin 2 of U2110 comes from plug P2540 pin 4. Looking over the A2500 board shows that pin 4 goes to chassis ground. Why would pin 2 from U2110 go all the way back to A2500 to reach chassis ground.

Anyway, the A2000 board seems to be working, albeit the frequency of the clock oscillator is not 200kHz as the diagram shows, it is running at 153.7kHz, though amplitude is good at 5 volts, I would think that would affect calibration but not operation. Back on A2100, the tuning control voltage at R2104 is good, it swings from + - 9.6 volts. The output of U2110 swings + - 10.7 volts. The DCPL Supply rails 15, -15, and 5 volts are all good. The reference voltage at the cathode of VR2115 (Zener) is 3.1, not the 3.3 volts is shows. Voltage at TP 2100, (output of U2130) is 11.65, a bit higher than the listed 11.3 volts. The voltages around the N-channel FET (Q2120) is Drain = 3.37 volts, Source = -3.1 volts, and Gate = -3.5 volts, are those in the ball park?

Needless to say there is NO signals present, waveform, 1, 2, 3, and 4 are all missing. Lines 'E' and 'F' are both quiet, the voltages on 'E' are 7.08 volts, on 'F' the voltage is 5.12 volts which swings a bit higher when I adjust center frequency, up to 5.44 volts. Of course 'E' has no signal as would be expected without drive from U2145 there is nothing to trigger the multivibrator U2030 on board A2000 sending a signal back up line 'F'. I keep thinking of this in terms of a frequency counter, I keep thinking there should be a driving input signal. I try to keep in mind it's a voltmeter, and keep in mind the circuit description given in the manual. It describes a ramp signal coming from the output of U2110, I don't understand that statement. The 'Tune' voltage is just a DC voltage, plus to minus. The minus input of U2120 goes to chassis ground??? What 'RAMP' are they speaking about?

Lastly the manual's circuit description on page 5-10 talks about a positive going ramp from U2110, aren't these just DC levels, what 'Ramp' are they talking about?

Okay, I see there are a lot of questions here. I had better post this and hope for the best. It's a great 7L13, it works well, but without a 'Center' frequency display, it's pretty much just a toy. Also, I do appreciate the feedback~!~ I am not accustom to working on test equipment, my experience has been mostly all in Hi-Fi, but this has been very interesting.

Thanks again VERY MUCH...
~Michael - AF7U







--- In TekScopes@..., "Michael" <af7u@> wrote:

I sure appreciate the input, I will give everything a go once I get it on my bench. Should be this weekend or first of next week. Thanks again,
~Michael



--- In TekScopes@..., "Christopher Hilton-Johnson" <chj@> wrote:

Also make sure that the 2 boards, A2100 DVM analog board and A2000, DVM
logic & readout board are only connected/touching where they should.
There needs to be a small space (say 1mm or less) between each - a piece
of thin card between the two will suffice. If the boards touch the
display can freeze, you can lose the units digit on the SA (although the
7Kxx readout still works). OP is spot on - also remove clean & reseat
the A2000 board actives.

Beyond that you need to start looking at the A2100 board & follow the
volts! The manual gives an excellent description of what should happen.
On the basis that neither readout works, it is more likely the A2100,
analog board you need to look at.

Chris HJ



My 7L13 display was cured by pulling and reseating the DIPs on the RO
board. IC pins were visibly tarnished. Symptoms not as complete as
yours, but AFAIR the display would intermittently 'freeze' while tuning
continued.

--- In TekScopes@... <mailto:TekScopes%40yahoogroups.com> ,
"Michael" wrote:

Hi all,
I have a 7L13 Spectrum Analyzer out in the field, it's not in front of

me right now but I will pick it up later this week. I've seen the unit
and the 'Center Frequency' LED read-out is stuck, and reads '0000', also
the same value is being sent to the CRT display. The analyzer is sitting
in a 7000 series mainframe and the mainframe works fine in every other
way. In fact, the spectrum analyzer works fine, just the 'Center
Frequency' display stays on zeros. The 'Tuning' works and adjusts
correctly. It is used with a TR-502 and that combination also works, you
just don't know where you are frequency wise. You can place a frequency
counter on the AUX out of the TR-502 and manually scan the bandwidth and
read the frequency on the counter. It appears everything is fine, just
the readout is non-functional, or at least stuck on zeros. I thought it
was curious the display in the 7000 is also reading zeros too. I will
have it in front of me next week but I thought I would see if anyone had
any thoughts before I open it up.

Thanks in advance,
~Michael - AF7U

o virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2238 / Virus Database: 2639/5618 - Release Date:
02/20/13

?

hi night walker is it not possible to do with HP 8656B signal generator...and not with the sg503 +sg504 that is much to expensive indead.. the comp. part i knew..

----- Original Message -----

From: machineguy59

To: TekScopes@...

Sent: Monday, March 11, 2013 1:24 AM

Subject: [TekScopes] Re: New here with a 2465 to clean up

?

Yes, I followed the service manual directions, loosened the nut on the collet, held my breath and pulled twice at 90 degrees rotations. The second pull let go and the fan came off clean. Guess I was living right today. I cna take pics if it will help anyone. I would try to make impression molds if someone wants to model this for a 3D printer.

I also got a chance to measure voltages and rough measures of ripple on J119, the test point for the main board. All values are almost in spec except for pin 11 the -8 volt supply to the channel 1 and 2 inputs. There I found the voltage at -6.4 volts (as I reported before) with a triangle waveform riding on top of over 150 millivolts. I am convinced this is the same waveform that corrupts the Ch1 and Ch2 traces. Now I have to separate cause from effect (is the power corrupt because its overloaded or is the regulator faulty). I also measured the voltage supply at U160 and found this tringle wave on the DC power. Overall, good progress for today.

I think my next step will be to tear down the LVPS to repair the fan and inspect the -8 volt regulator while its apart. My goal is to correct the power supply before replacing all the electrolytic and film caps.

--- In TekScopes@..., "Tom Miller" wrote:
>
> There are no brushes in that motor.
>
> There is an end play adjustment on the rear bearing but it requires removal of the pc board to get to.
> Did the fan just pull off the shaft?
>
> T
>
> ----- Original Message -----
> From: machineguy59
> To: TekScopes@...
> Sent: Sunday, March 10, 2013 6:14 PM
> Subject: [TekScopes] Re: New here with a 2465 to clean up
>
>
>
> I will post my experience repairing the fan when I have it completed. But for now, the fan and squirrel cage appear to be intact. The collet is functional although I have not taken the jaws out of the sleeve yet. I was careful removing them and it all looks good to me.
>
> I suspect either the motor windings (not likley I think), the motor "brushes" (more likely), or the drive transistors (what I am hoping for). I will keep my fingers crossed.
>
> --- In TekScopes@..., "Tom Miller" wrote:
> >
> > We will be interested in how you resolve the fan problem.
> >
> > it is a well known issue. Most likely the plastic fan collet has broken.
> > Hey, I wonder if this part (or something similar) could be made with the 3D printer?
> >
> >
> > Tom
> >
> > ----- Original Message -----
> > From: machineguy59
> > To: TekScopes@...
> > Sent: Sunday, March 10, 2013 2:05 PM
> > Subject: [TekScopes] Re: New here with a 2465 to clean up
> >
> >
> >
> > You guys are super. Thanks you again for the warm welcome and helpful advice. I finally got some time to apply some of it and want to give you a status update.
> >
> > First, I dismantled the front control panel and cleaned everything. There was a minor amount of residue from an old spill (I feared it would be worse) but overall the inside is remarkably clean. I did find that someone had previously glued some knob covers to their inserts and they broke during tear down. I plan to order replacements but I CAN glue them back if necessary.
> >
> > Second, I built a heat sink for U800 by modifying an old heat sonk from a computer video board. It was messsy to cut notches for adjacent parts but it was worth it. I have a heat sink that fits well and seems to work well. It screws to the same screws that hold the U800 but I was careful to no overtighten. I can post or mail pictures if anyone is interested.
> >
> > Third, Patrick, your advice to measure voltages on J119 (the test point for regulated low voltage on the mainboard) is spot on. The -8 volt supply is only at -6.4 volts (a 20% error). Also, several voltages have ripple that is far out of spec (I didnt record actual values but will before repairs are started). My review of the schematics shows that -8 supply only feeds the two vertical pre-amps (U100 and U200) and the op amp that sets paramters for VAR gain and DC ballance (U160). My conclusion is that you were right, the -8 volt supply is failing (probably the output filter cap) and this drooping voltage causes the vertical pre-amp gains to be off and variable. Alternatively, one of the preamps or the op amp is overloading the supply but this seems unlikely since other preamp functions are working.
> >
> > Fourth, I ordered new caps for the entire LVPS (both boards). The spead sheet posted at Tekarc was very helpful and still relevant. All parts are still available at Mouser. I verified this list with the service manual for the 2465 and found I need two additional caps (C1112, and C1050). I also chose to order replacements for the ceramic caps but will probably not change them out since ceramics seem to have a long life expectancy. I apprecaiate any advice on this decision.
> >
> > Fifth, I found that the case fan is not running. The shaft turns freely and feels to run smoothly but the fan does not turn. If I give it a spin by hand it just stops with no apparent self motivation. So I have a fan to repair. Its one of the "original" designs with a separate transistorized drive board. These were very quiet fans so I will try to restore this one.
> >
> > So work continues in my spare time. I expect a complete restoration will be possible. I will post updates of my progress along the way. But I wanted to post this thank you for the excellent help I have received from this group. I would not take on this project without your advice.
> >
> > Mac
> >
> >
> > --- In TekScopes@..., "Patrick Wong" wrote:
> > >
> > > Hi Mac,
> > >
> > > I recommend that you add qservice.tv as a favorite in your browser because you can get lots of useful information about Tektronix scopes there.
> > >
> > > For example, you will see that the part number for the 2465 low voltage power supply has a slightly different suffix compared to the LVPS for the 2465A and 2465B. Therefore I would not assume that a parts list compiled for a 2465B will work 100% for your unit. It might be 95% correct, or might be further off.
> > >
> > > When I worked on the LVPS for my 2465A and 2467 I found small differences between the capacitors. There were a few non-polarized electrolytics in the 2465A power supply. Both scopes were built in mid-1988. Therefore, even within the 2465A/2467 generation, you cannot count on the LV power supplies being identical with regards to capacitor content.
> > >
> > > I also recommend you replace the two AC X2 line filtering capacitors as you will probably see the yellow transparent plastic body has lots of cracking. This is a potential failure area especially in Europe where the AC line voltage is 220V or more.
> > >
> > > With regards to the CH1 and CH2 gain problem, I doubt the preamp hybrids are the problem. Assuming the 2465 has similar circuitry as 2465A in this area, I suggest you look at U160, a quad op-amp which controls the gain and DC balance for U100 and U200 (see schematic #4 which shows the vertical attenuators and preamp section.) U160 is powered by the +15V and -8V power supplies (see the power distribution diagram) so a problem with either of those two may help explain the gain problem you noticed.
> > >
> > > Meanwhile the CH3/CH4 hybrid is powered by the +5V and -5V supplies.
> > >
> > > Does your A5 board have a lithium battery soldered to one end? If so, that maintains calibration constants.
> > >
> > > Assuming the battery is original, I suggest you add a replacement battery to your parts ordering form. You will need to maintain voltage with a lab power supply while unsoldering and replacing the battery (using a non-grounded soldering iron.)
> > >
> > > Good luck,
> > >
> > > Patrick Wong AK6C
> > >
> > > --- In TekScopes@..., "machineguy59" wrote:
> > > >
> > > > ...That parts list is for a 2365B but it looks to me that it will also work for a 2465. Does anyone know if there are differences?
> > > >
> > > > Then, with the heat sink on U800 and the knowledge the glue is cleaned out, I will resume the quest to find why the gain is messed up on Ch 1 and Ch 2. This gain on Ch ! and Ch 2 is my only serious concer for the scope.
> > >
> >
>

I sure appreciate the input, I will give everything a go once I get it on my bench. Should be this weekend or first of next week. Thanks again,
~Michael



--- In TekScopes@..., "Christopher Hilton-Johnson" <chj@> wrote:

Also make sure that the 2 boards, A2100 DVM analog board and A2000, DVM
logic & readout board are only connected/touching where they should.
There needs to be a small space (say 1mm or less) between each - a piece
of thin card between the two will suffice. If the boards touch the
display can freeze, you can lose the units digit on the SA (although the
7Kxx readout still works). OP is spot on - also remove clean & reseat
the A2000 board actives.

Beyond that you need to start looking at the A2100 board & follow the
volts! The manual gives an excellent description of what should happen.
On the basis that neither readout works, it is more likely the A2100,
analog board you need to look at.

Chris HJ



My 7L13 display was cured by pulling and reseating the DIPs on the RO
board. IC pins were visibly tarnished. Symptoms not as complete as
yours, but AFAIR the display would intermittently 'freeze' while tuning
continued.

--- In TekScopes@... <mailto:TekScopes%40yahoogroups.com> ,
"Michael" wrote:

Hi all,
I have a 7L13 Spectrum Analyzer out in the field, it's not in front of

me right now but I will pick it up later this week. I've seen the unit
and the 'Center Frequency' LED read-out is stuck, and reads '0000', also
the same value is being sent to the CRT display. The analyzer is sitting
in a 7000 series mainframe and the mainframe works fine in every other
way. In fact, the spectrum analyzer works fine, just the 'Center
Frequency' display stays on zeros. The 'Tuning' works and adjusts
correctly. It is used with a TR-502 and that combination also works, you
just don't know where you are frequency wise. You can place a frequency
counter on the AUX out of the TR-502 and manually scan the bandwidth and
read the frequency on the counter. It appears everything is fine, just
the readout is non-functional, or at least stuck on zeros. I thought it
was curious the display in the 7000 is also reading zeros too. I will
have it in front of me next week but I thought I would see if anyone had
any thoughts before I open it up.

Thanks in advance,
~Michael - AF7U

o virus found in this message.
Checked by AVG - www.avg.com
Version: 2012.0.2238 / Virus Database: 2639/5618 - Release Date:
02/20/13

?

I have had a Variac that I use. I also understand most if not all of the recent conversation. It has however gotten me thinking…

?

I have also been working towards an isolation transformer to add to my benches front end... However, I am now thinking along the lines of implementing the circuit a member posted here several weeks ago. It seemed to have all bases covered. Variable power, inline light bulbs, power measurement, isolation, etc.

????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????& nbsp;??????? ??????????????

Anyway, my question is: Is an isolation transformer necessary if a person was to put/have a GFI up in front of everything? Since a lot of my early experience was ?around TV’s that could have hot chassis depending on which way they were plugged in I am pretty cognizant on testing ground to ground voltage before I do work. I know an isolation transformer makes this more or less idiot proof (with-in reason). Would (or does) a GFI serve the same purpose? GFI’s probably existed when I was doing fulltime electronics but were not utilized much. Therefore I am not versed in their capabilities and or exactly what makes them trip? I do know they trip due to current flow on the ground leg, however, I do not know if that covers a ground loop from chassis to chassis. ?I realize I could research myself but I bet someone here knows the pros and cons of GFI vs. Isolation transformer off the top of their head and could feed me the answer. (assuming they wouldn’t mind letting me cheat that way). Actually there is probably talent enough here to pass for authority on the subject.

?

If too off topic please reply off forum.

There are no brushes in that motor.

There is an end play adjustment on the rear bearing but it requires removal of the pc board to get to.
Did the fan just pull off the shaft?

T

----- Original Message -----
From: machineguy59
To: TekScopes@...
Sent: Sunday, March 10, 2013 6:14 PM
Subject: [TekScopes] Re: New here with a 2465 to clean up



I will post my experience repairing the fan when I have it completed. But for now, the fan and squirrel cage appear to be intact. The collet is functional although I have not taken the jaws out of the sleeve yet. I was careful removing them and it all looks good to me.

I suspect either the motor windings (not likley I think), the motor "brushes" (more likely), or the drive transistors (what I am hoping for). I will keep my fingers crossed.

--- In TekScopes@..., "Tom Miller" <tmiller11147@> wrote:
>
> We will be interested in how you resolve the fan problem.
>
> it is a well known issue. Most likely the plastic fan collet has broken.
> Hey, I wonder if this part (or something similar) could be made with the 3D printer?
>
>
> Tom
>
> ----- Original Message -----
> From: machineguy59
> To: TekScopes@...
> Sent: Sunday, March 10, 2013 2:05 PM
> Subject: [TekScopes] Re: New here with a 2465 to clean up
>
>
>
> You guys are super. Thanks you again for the warm welcome and helpful advice. I finally got some time to apply some of it and want to give you a status update.
>
> First, I dismantled the front control panel and cleaned everything. There was a minor amount of residue from an old spill (I feared it would be worse) but overall the inside is remarkably clean. I did find that someone had previously glued some knob covers to their inserts and they broke during tear down. I plan to order replacements but I CAN glue them back if necessary.
>
> Second, I built a heat sink for U800 by modifying an old heat sonk from a computer video board. It was messsy to cut notches for adjacent parts but it was worth it. I have a heat sink that fits well and seems to work well. It screws to the same screws that hold the U800 but I was careful to no overtighten. I can post or mail pictures if anyone is interested.
>
> Third, Patrick, your advice to measure voltages on J119 (the test point for regulated low voltage on the mainboard) is spot on. The -8 volt supply is only at -6.4 volts (a 20% error). Also, several voltages have ripple that is far out of spec (I didnt record actual values but will before repairs are started). My review of the schematics shows that -8 supply only feeds the two vertical pre-amps (U100 and U200) and the op amp that sets paramters for VAR gain and DC ballance (U160). My conclusion is that you were right, the -8 volt supply is failing (probably the output filter cap) and this drooping voltage causes the vertical pre-amp gains to be off and variable. Alternatively, one of the preamps or the op amp is overloading the supply but this seems unlikely since other preamp functions are working.
>
> Fourth, I ordered new caps for the entire LVPS (both boards). The spead sheet posted at Tekarc was very helpful and still relevant. All parts are still available at Mouser. I verified this list with the service manual for the 2465 and found I need two additional caps (C1112, and C1050). I also chose to order replacements for the ceramic caps but will probably not change them out since ceramics seem to have a long life expectancy. I apprecaiate any advice on this decision.
>
> Fifth, I found that the case fan is not running. The shaft turns freely and feels to run smoothly but the fan does not turn. If I give it a spin by hand it just stops with no apparent self motivation. So I have a fan to repair. Its one of the "original" designs with a separate transistorized drive board. These were very quiet fans so I will try to restore this one.
>
> So work continues in my spare time. I expect a complete restoration will be possible. I will post updates of my progress along the way. But I wanted to post this thank you for the excellent help I have received from this group. I would not take on this project without your advice.
>
> Mac
>
>
> --- In TekScopes@..., "Patrick Wong" <patwong3@> wrote:
> >
> > Hi Mac,
> >
> > I recommend that you add qservice.tv as a favorite in your browser because you can get lots of useful information about Tektronix scopes there.
> >
> > For example, you will see that the part number for the 2465 low voltage power supply has a slightly different suffix compared to the LVPS for the 2465A and 2465B. Therefore I would not assume that a parts list compiled for a 2465B will work 100% for your unit. It might be 95% correct, or might be further off.
> >
> > When I worked on the LVPS for my 2465A and 2467 I found small differences between the capacitors. There were a few non-polarized electrolytics in the 2465A power supply. Both scopes were built in mid-1988. Therefore, even within the 2465A/2467 generation, you cannot count on the LV power supplies being identical with regards to capacitor content.
> >
> > I also recommend you replace the two AC X2 line filtering capacitors as you will probably see the yellow transparent plastic body has lots of cracking. This is a potential failure area especially in Europe where the AC line voltage is 220V or more.
> >
> > With regards to the CH1 and CH2 gain problem, I doubt the preamp hybrids are the problem. Assuming the 2465 has similar circuitry as 2465A in this area, I suggest you look at U160, a quad op-amp which controls the gain and DC balance for U100 and U200 (see schematic #4 which shows the vertical attenuators and preamp section.) U160 is powered by the +15V and -8V power supplies (see the power distribution diagram) so a problem with either of those two may help explain the gain problem you noticed.
> >
> > Meanwhile the CH3/CH4 hybrid is powered by the +5V and -5V supplies.
> >
> > Does your A5 board have a lithium battery soldered to one end? If so, that maintains calibration constants.
> >
> > Assuming the battery is original, I suggest you add a replacement battery to your parts ordering form. You will need to maintain voltage with a lab power supply while unsoldering and replacing the battery (using a non-grounded soldering iron.)
> >
> > Good luck,
> >
> > Patrick Wong AK6C
> >
> > --- In TekScopes@..., "machineguy59" <machineguy59@> wrote:
> > >
> > > ...That parts list is for a 2365B but it looks to me that it will also work for a 2465. Does anyone know if there are differences?
> > >
> > > Then, with the heat sink on U800 and the knowledge the glue is cleaned out, I will resume the quest to find why the gain is messed up on Ch 1 and Ch 2. This gain on Ch ! and Ch 2 is my only serious concer for the scope.
> >
>

----- Original Message -----

From: Don Black

To: TekScopes@...

Sent: Monday, March 11, 2013 12:25 AM

Subject: Re: [TekScopes] Re: Question associated with all of the Variac talk.

?

The point is if the active and neutral currents aren't equal, the difference normally flows to ground, either via the ground lead or you.

Don Black.

On 11-Mar-13 2:02 PM, sipespresso wrote:

?

I believe a GFI trips when the currents in the neutral and hot wires aren't equal. It doesn't directly have to do with current in the ground leg, as far as I know. -Kurt

--- In TekScopes@..., "Rob" wrote:

> I do know they trip due to current flow on
> the ground leg

?

I believe a GFI trips when the currents in the neutral and hot wires aren't equal. It doesn't directly have to do with current in the ground leg, as far as I know. -Kurt

--- In TekScopes@..., "Rob" wrote:

> I do know they trip due to current flow on
> the ground leg