Topics

FG 504 problems


Colin Herbert
 

I am labeling this as "problems" because while I have one or two current problems that I am puzzling over, I am sure that I will have more queries to add until I get this Function Generator working right.
My current puzzle relates to a jumper on the A3 Loop Board labelled "W20 Phase lock Jumper". This jumper, according to the Service Manual, allows the VCF Input to function as a phase modulating input. While its position is shown on the Internal Adjustments section A3 Loop Board diagram, there appears to be no indication of which is the default setting and which the VCF input setting. I cannot locate the jumper on the schematics either. Can anyone please enlighten me?
TIA, Colin.


Dan G
 

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan


Colin Herbert
 

Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan G
Sent: 08 August 2020 01:15
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan


Chuck Harris
 

Tektronix never gets all of the information you need in
anything but the most trivial manuals.

Between what they withhold for proprietary reasons, what
they put in odd places, what they got plain wrong, and
what they simply didn't get around to documenting, there
is always something missing... something to wish for.

I needed access to the boards on a FG504 I am currently
repairing, and so I pulled the cables off of the floating
power supply board and removed it...

It took me an hour to trace all of the unlabeled connectors
back to their origin, so that I could figure out which one
went on which pin.

Yes, I know, I should have taken a picture... but I had another
FG504 in for repair so I figured I could just crib off of it...
except that someone had beaten me to it, and removed all of
the same connectors on that unit... OOPSIE!

Honestly, I am pretty happy that Tektronix did as good of a
job as they did on including pertinent information in their
manuals... I'll hold them to perfection when I can achieve
perfection myself.

-Chuck Harris

Colin Herbert via groups.io wrote:

Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan G
Sent: 08 August 2020 01:15
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan








John Ferguson
 

the next step will be to discover the unobtanium part needed in one of the FG504's is also bad in the other.

john

On 8/8/20 9:06 AM, Chuck Harris wrote:
Tektronix never gets all of the information you need in
anything but the most trivial manuals.

Between what they withhold for proprietary reasons, what
they put in odd places, what they got plain wrong, and
what they simply didn't get around to documenting, there
is always something missing... something to wish for.

I needed access to the boards on a FG504 I am currently
repairing, and so I pulled the cables off of the floating
power supply board and removed it...

It took me an hour to trace all of the unlabeled connectors
back to their origin, so that I could figure out which one
went on which pin.

Yes, I know, I should have taken a picture... but I had another
FG504 in for repair so I figured I could just crib off of it...
except that someone had beaten me to it, and removed all of
the same connectors on that unit... OOPSIE!

Honestly, I am pretty happy that Tektronix did as good of a
job as they did on including pertinent information in their
manuals... I'll hold them to perfection when I can achieve
perfection myself.

-Chuck Harris

Colin Herbert via groups.io wrote:
Thanks for that info, Dan. Would you believe that when my wife brought me a mug of tea in bed this morning, I was reading the FG 504 Manual and noticed where the jumper is marked on the schematic. I think I was thrown as to its circuit location by the physical location on the circuit board. However, that revelation left me with the puzzle of which was the default (non-VCF) position and I was wondering as to how I might investigate that, when I looked at my email and your reply gave me the answer!

I still have some problems with the Function Generator (though I have fixed one) which relate to the symmetry adjustments.

An earlier problem involved the power-rails and one going bad after I'd measured it to be OK. That turned out to be a harmonica-type connector giving bad contact, so I re-seated all of those that I could locate, which solved that problem, but then left me with the question of whether I had put the W20 jumper back properly or not. You have now clarified that for me.

I wonder why this wasn't clearer in the Manual?

Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Dan G
Sent: 08 August 2020 01:15
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

On Fri, Aug 7, 2020 at 03:41 PM, Colin Herbert wrote:

While its position is shown on
the Internal Adjustments section A3 Loop Board diagram, there appears to be no
indication of which is the default setting and which the VCF input setting. I
cannot locate the jumper on the schematics either.
Hi Colin,

The W20 jumper is shown on schematic <1> ("Triangle Wave Generator" in
post-B040000 service manuals, and "Main Loop" in early editions.) It
is shown in the upper left corner of the schematic, just above "VCF INPUT".

The jumper is in the N/C position when it is placed toward the back of the
plug-in. Moving it to the front of the plug-in routes the VCF Input signal
to P1275.


dan








Colin Herbert
 

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.


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.


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/


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/


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.


tenareze32@...
 

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


Stephen
 

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


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@...> 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!!!


Stephen
 

On Sat, Aug 22, 2020 at 04:08 AM, Colin Herbert wrote:


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.
Understandable.

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.
Since someone here sent me a link to this document, it’s almost become my bedside book! 😂😂😂


 

On Sat, Aug 22, 2020 at 03:09 PM, Stephen wrote:


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.
I just added a version of that document with bookmarks on the TekWiki page:

http://w140.com/tekwiki/wiki/Common_Design_Parts_Catalogs

I think the original version may be removed

Raymond


 

On Sat, Aug 22, 2020 at 06:24 PM, Raymond Domp Frank wrote:


I just added a version of that document with bookmarks on the TekWiki page:

http://w140.com/tekwiki/wiki/Common_Design_Parts_Catalogs

I think the original version may be removed
At least in my Chrome browser, the bookmarks aren't shown online. Firefox and downloaded document are ok.

Raymond


Colin Herbert
 

Has anyone ever tried cleaning the contacts on the "Frequency Multiplier" switch? They are (I'm sure) cam-type switches and are probably rather similar to the "Attenuator" switch contacts. The problem is access. While the "Attenuator" contacts are easy to get at and use the "paper soaked in isopropanol trapped between the contacts" technique, the "Frequency Multiplier" contacts can barely be seen. While I can't detect any higher-resistance situations, I'm wondering if (since these contacts are on a pcb, not like the attenuators in the 400-series scopes which are on a sensitive substrate) a few gentle and sparing squirts of Servisol would be a good or a bad idea?
Any opinions welcome.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Colin Herbert via groups.io
Sent: 22 August 2020 10:32
To: TekScopes@groups.io
Subject: Re: [TekScopes] FG 504 problems

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.