CFG253 vs CFG250 schematic


Chris Elmquist
 

I recently received a CFG253 function generator that is kinda cute and
goes along with the CMC250 frequency counter I've had for eons.

Unfortunately, the CFG253 has some issues-- namely, no oscillations on
the 100, 10 and 1 ranges and some distortion in sine mode on other ranges.
So, I'd like to fix it up.

I can't find a schematic for CFG253 but I did for CFG250. Can anyone
comment on how different they may really be? I suspect very similar
with only some component differences to achieve the higher frequency
capability in the '253??

If anyone knows a source for a CFG253 schematic, that would be greatly
appreciated too. I have found a Service Bulletin that discusses some
alignment operations but no actual schematic with component values so far.

Chris
--
Chris Elmquist NØJCF


Tom Lee
 

If it works on some ranges but not others, I’d suspect switches first. So before diving too deeply into the debug, first do the Deoxit dance. That might fix up the range-setting dependent sine distortion as well.

Of course, check the supplies, etc. to make sure that bypass caps are doing what they’re supposed to do, and the regulators are regulating, etc. But it sounds like this should be a pretty easy fix.

Cheers,
Tom

Sent from my iThing, so please forgive typos and brevity.

On May 20, 2021, at 1:17 PM, Chris Elmquist <chrise@pobox.com> wrote:

I recently received a CFG253 function generator that is kinda cute and
goes along with the CMC250 frequency counter I've had for eons.

Unfortunately, the CFG253 has some issues-- namely, no oscillations on
the 100, 10 and 1 ranges and some distortion in sine mode on other ranges.
So, I'd like to fix it up.

I can't find a schematic for CFG253 but I did for CFG250. Can anyone
comment on how different they may really be? I suspect very similar
with only some component differences to achieve the higher frequency
capability in the '253??

If anyone knows a source for a CFG253 schematic, that would be greatly
appreciated too. I have found a Service Bulletin that discusses some
alignment operations but no actual schematic with component values so far.

Chris
--
Chris Elmquist NØJCF






Chris Elmquist
 

On Thursday (05/20/2021 at 01:33PM -0700), Tom Lee wrote:
If it works on some ranges but not others, I’d suspect switches first. So before diving too deeply into the debug, first do the Deoxit dance. That might fix up the range-setting dependent sine distortion as well.

Of course, check the supplies, etc. to make sure that bypass caps are doing what they’re supposed to do, and the regulators are regulating, etc. But it sounds like this should be a pretty easy fix.
Yes. Agreed. The sine distortion is "flat topping" on just the high
side of the sine curve so that further suggests a power supply issue
and maybe the +15 is not making it all the way to somewhere.

The switches do seem pretty firm and tight and, at least according to
the '250 schematic I have, the 100, 10 and 1 ranges have one capacitor
in common (a 1uF) so that is on my suspect list too.

And for sure, I can likely make this go without a schematic but I always
try to collect as much documentation as I can for all the gear I have.

Thanks,

Chris NØJCF

Sent from my iThing, so please forgive typos and brevity.

On May 20, 2021, at 1:17 PM, Chris Elmquist <chrise@pobox.com> wrote:

I recently received a CFG253 function generator that is kinda cute and
goes along with the CMC250 frequency counter I've had for eons.

Unfortunately, the CFG253 has some issues-- namely, no oscillations on
the 100, 10 and 1 ranges and some distortion in sine mode on other ranges.
So, I'd like to fix it up.

I can't find a schematic for CFG253 but I did for CFG250. Can anyone
comment on how different they may really be? I suspect very similar
with only some component differences to achieve the higher frequency
capability in the '253??

If anyone knows a source for a CFG253 schematic, that would be greatly
appreciated too. I have found a Service Bulletin that discusses some
alignment operations but no actual schematic with component values so far.

Chris
--
Chris Elmquist NØJCF







--
Chris Elmquist


Tom Lee
 

I went through my files to see if I had any info on the CFG253, but all I had was a note: "No schematics available. Allegedly based on the FG503". I have no idea where I got the alleged information, though, so it may not be reliable. But you might want to take a look at the manual for that TM500 plug-in (which is available on tekwiki), and see if you get lucky.

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/20/2021 17:09, Chris Elmquist wrote:
On Thursday (05/20/2021 at 01:33PM -0700), Tom Lee wrote:
If it works on some ranges but not others, I’d suspect switches first. So before diving too deeply into the debug, first do the Deoxit dance. That might fix up the range-setting dependent sine distortion as well.

Of course, check the supplies, etc. to make sure that bypass caps are doing what they’re supposed to do, and the regulators are regulating, etc. But it sounds like this should be a pretty easy fix.
Yes. Agreed. The sine distortion is "flat topping" on just the high
side of the sine curve so that further suggests a power supply issue
and maybe the +15 is not making it all the way to somewhere.

The switches do seem pretty firm and tight and, at least according to
the '250 schematic I have, the 100, 10 and 1 ranges have one capacitor
in common (a 1uF) so that is on my suspect list too.

And for sure, I can likely make this go without a schematic but I always
try to collect as much documentation as I can for all the gear I have.

Thanks,

Chris NØJCF

Sent from my iThing, so please forgive typos and brevity.

On May 20, 2021, at 1:17 PM, Chris Elmquist <chrise@pobox.com> wrote:

I recently received a CFG253 function generator that is kinda cute and
goes along with the CMC250 frequency counter I've had for eons.

Unfortunately, the CFG253 has some issues-- namely, no oscillations on
the 100, 10 and 1 ranges and some distortion in sine mode on other ranges.
So, I'd like to fix it up.

I can't find a schematic for CFG253 but I did for CFG250. Can anyone
comment on how different they may really be? I suspect very similar
with only some component differences to achieve the higher frequency
capability in the '253??

If anyone knows a source for a CFG253 schematic, that would be greatly
appreciated too. I have found a Service Bulletin that discusses some
alignment operations but no actual schematic with component values so far.

Chris
--
Chris Elmquist NØJCF







Mark Vincent
 

Chris,

Tom Lee is right about cleaning the switches. That will ensure they are making contact.

If your power supply is bad, I suggest Nichicon UHE for the caps. The output filters of the two regulators can be a ULD 47mfd. The originals are 10mfd. These two can be raised in value. If the 1mfd you mention is electrolytic, put in a 80-R82DC4100DQ70J. This is a film. The original electrolytics are made by Suscon, a cheap off-brand. These look good and can be bad. I have this model. It is a copy of Kenwood model.

Mark


Tom Lee
 

I see in checking online pics of the various units that the exteriors of the CFG-250 and CFG-253 are virtually identical. I think that the note I had about the FG-503 is not to be trusted. The service manual for the -250 is available on tekwiki, so if you're lucky, the schematics, parts lists and parts locators might be close enough for you to get what you need.

By the way, I've encountered plenty of pushbuttons that feel just fine, but don't work right. The amount of oxide that causes electrical problems is much smaller than what might produce mechanically noticeable effects. I'm hoping that Deoxit takes care of at least some of what you're seeing.

In any case, good luck!

-- Cheers,
Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 5/20/2021 17:09, Chris Elmquist wrote:
On Thursday (05/20/2021 at 01:33PM -0700), Tom Lee wrote:
If it works on some ranges but not others, I’d suspect switches first. So before diving too deeply into the debug, first do the Deoxit dance. That might fix up the range-setting dependent sine distortion as well.

Of course, check the supplies, etc. to make sure that bypass caps are doing what they’re supposed to do, and the regulators are regulating, etc. But it sounds like this should be a pretty easy fix.
Yes. Agreed. The sine distortion is "flat topping" on just the high
side of the sine curve so that further suggests a power supply issue
and maybe the +15 is not making it all the way to somewhere.

The switches do seem pretty firm and tight and, at least according to
the '250 schematic I have, the 100, 10 and 1 ranges have one capacitor
in common (a 1uF) so that is on my suspect list too.

And for sure, I can likely make this go without a schematic but I always
try to collect as much documentation as I can for all the gear I have.

Thanks,

Chris NØJCF

Sent from my iThing, so please forgive typos and brevity.

On May 20, 2021, at 1:17 PM, Chris Elmquist <chrise@pobox.com> wrote:

I recently received a CFG253 function generator that is kinda cute and
goes along with the CMC250 frequency counter I've had for eons.

Unfortunately, the CFG253 has some issues-- namely, no oscillations on
the 100, 10 and 1 ranges and some distortion in sine mode on other ranges.
So, I'd like to fix it up.

I can't find a schematic for CFG253 but I did for CFG250. Can anyone
comment on how different they may really be? I suspect very similar
with only some component differences to achieve the higher frequency
capability in the '253??

If anyone knows a source for a CFG253 schematic, that would be greatly
appreciated too. I have found a Service Bulletin that discusses some
alignment operations but no actual schematic with component values so far.

Chris
--
Chris Elmquist NØJCF







Chris Elmquist
 

On Thursday (05/20/2021 at 08:18PM -0700), Tom Lee wrote:
I see in checking online pics of the various units that the exteriors of the
CFG-250 and CFG-253 are virtually identical. I think that the note I had
about the FG-503 is not to be trusted. The service manual for the -250 is
available on tekwiki, so if you're lucky, the schematics, parts lists and
parts locators might be close enough for you to get what you need.

By the way, I've encountered plenty of pushbuttons that feel just fine, but
don't work right. The amount of oxide that causes electrical problems is
much smaller than what might produce mechanically noticeable effects. I'm
hoping that Deoxit takes care of at least some of what you're seeing.

In any case, good luck!
Yes. Thanks guys. I will explore these avenues and I appreciate the
suggestions on the replacement caps too. Switches will get the DeoxIT
treatment for sure as that is easy.

I have the CFG250 service manual with schematic and so my original query
was mostly to understand what components might be different between
the two. I think it is pretty safe to assume they are of a very similar
design.

I also have an FG502 in a TM-500 chassis and it is true that they have
nearly identical functions, inputs and outputs but will need to discover
more about actual implementation similarities.

Thanks again. I'll report back when I have had some time to poke around
in it.

Chris NØJCF


On 5/20/2021 17:09, Chris Elmquist wrote:
On Thursday (05/20/2021 at 01:33PM -0700), Tom Lee wrote:
If it works on some ranges but not others, I’d suspect switches first. So before diving too deeply into the debug, first do the Deoxit dance. That might fix up the range-setting dependent sine distortion as well.

Of course, check the supplies, etc. to make sure that bypass caps are doing what they’re supposed to do, and the regulators are regulating, etc. But it sounds like this should be a pretty easy fix.
Yes. Agreed. The sine distortion is "flat topping" on just the high
side of the sine curve so that further suggests a power supply issue
and maybe the +15 is not making it all the way to somewhere.

The switches do seem pretty firm and tight and, at least according to
the '250 schematic I have, the 100, 10 and 1 ranges have one capacitor
in common (a 1uF) so that is on my suspect list too.

And for sure, I can likely make this go without a schematic but I always
try to collect as much documentation as I can for all the gear I have.

Thanks,

Chris NØJCF

Sent from my iThing, so please forgive typos and brevity.

On May 20, 2021, at 1:17 PM, Chris Elmquist <chrise@pobox.com> wrote:

I recently received a CFG253 function generator that is kinda cute and
goes along with the CMC250 frequency counter I've had for eons.

Unfortunately, the CFG253 has some issues-- namely, no oscillations on
the 100, 10 and 1 ranges and some distortion in sine mode on other ranges.
So, I'd like to fix it up.

I can't find a schematic for CFG253 but I did for CFG250. Can anyone
comment on how different they may really be? I suspect very similar
with only some component differences to achieve the higher frequency
capability in the '253??

If anyone knows a source for a CFG253 schematic, that would be greatly
appreciated too. I have found a Service Bulletin that discusses some
alignment operations but no actual schematic with component values so far.

Chris
--
Chris Elmquist NØJCF
--
Chris Elmquist