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Tektronix FG507

C

Charles

"mike" wrote in message
Thanks mike. I always had a power light. The FG is still running (I will
not turn it off until later) as my project is not over and I don't want
to risk that it won't start again.

My guess is that the mainframe is OK as my other plug-ins all work fine.

The FG is repairable but difficult if there is no extender card available!
Click to expand...

I jumped to the "dead" conclusion.
You're likely right about the mainframe if you switched holes.
But don't generalize that to any failure modes. There are hole
specific functions that can cause problems.

You still need all the supplies working, so check that.
What were the exact symptoms of "not working"?
What was the output voltage? did it vary with offset/amplitude
settings? Did it vary with the frequency dial setting?
waveform settings changes?
See any output glitches when you changed frequency ranges?
What did the sweep settings do? It's possible for a failed
sweep to cut off the current to the ramp.
If there's a sweep output or a trigger output, see if anything
comes out there.

It's basically a pair of current sources charging a cap.
The triangle is the basic waveform function.
It gets "rounded off" for sine wave. Square comes out
of the peak comparator. Make the triangle work first.

It's a two-wide plugin. If it has two connectors out the back,
your extender problems multiply. Depending on the internal
connections between boards, you may need extenders there too.

Assume if you had a service manual, you'd have said so?
Try to find it.

For now, I am going to rule out the mainframe as all the other plug-ins are
working normally (PS501-1, PS502-2, SG503).

With no extender board, I don't think a service manual will help much.

Thanks again.
 
C

Charles

"Charles" wrote in message
I fired it up today and no joy. Took off all the covers/shields and tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely on
it now. Any suggestions?

Lots of helpful replies here, but looking for alternatives, I found this:
http://www.neobits.com/instek_sfg_2...html?atc=gbp&gclid=CJ-zsbKW17MCFRRbnAodpnoAgQ

No way that I am going to pay for a schematic/service manual (from a
questionable source) and pay for an adaptor to power the FG507 so I can work
on it when the link above promises so much more.

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

Thanks!
 
A

Archon

"Charles" wrote in message
I fired it up today and no joy. Took off all the covers/shields and
tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't
rely on
it now. Any suggestions?

Lots of helpful replies here, but looking for alternatives, I found
this:
http://www.neobits.com/instek_sfg_2...html?atc=gbp&gclid=CJ-zsbKW17MCFRRbnAodpnoAgQ


No way that I am going to pay for a schematic/service manual (from a
questionable source) and pay for an adaptor to power the FG507 so I can
work on it when the link above promises so much more.

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

Thanks!
Click to expand...

If you want help on this I suggest you apply to join the Yahoo Tekscopes
group, there is a fair amount of info onn tantalums that fail, Also it
appears this is a FG501A with sweep added so you could maybe use the
free download from BAMA.
 
M

mike

in message
I fired it up today and no joy. Took off all the covers/shields and tested
all the fuses and still no joy. Reseated all the connectors and ICs.

Finally, after repeated power on/off cycles it started to work.

Any ideas? I need this generator for an important project but can't rely on
it now. Any suggestions?

Lots of helpful replies here, but looking for alternatives, I found
this:
http://www.neobits.com/instek_sfg_2...html?atc=gbp&gclid=CJ-zsbKW17MCFRRbnAodpnoAgQ
Click to expand...
A function generator is a jack of all trades, master of none.
Choosing one is the art of minimizing the problems caused by the crappy
waveforms
in your specific application.
Without knowing which waveforms and functions are important to you and
what imperfections you
can tolerate, there's not much help anyone can provide.
The specs in large print on the datasheet usually don't tell the whole
story.
It's a lot like buying an automobile and expecting to actually get 40mpg.
No way that I am going to pay for a schematic/service manual (from a
questionable source) and pay for an adaptor to power the FG507 so I can
work on it when the link above promises so much more.

Repair is not always the best option. Recycling and replacement is
sometimes better. Sad. Really liked the FG507.

Thanks!
Click to expand...
If you're gonna scrap it, send it to me.
I'll fix it and add it to my collection of Tektronix Relics.
 
T

tm

Jeff Liebermann said:
You're willing to pay $400 for a replacement function generator, but
not $15 for a schematic to repair the one you currently own.

It's easy enough to calculate the relative cost of repair to replace.
My guess(tm) is that it would take me about 2 hrs and $20 in parts to
replace all the dip tantalum capacitors in the FG507. A little
Googling will show that old tantalums are a major problem in Tek
products. I value my spare time at $35/hr. That's $90 cost to repair
the FG507 without the risk of buying a manual from a questionable
source. Working blind does offer a challenge, but I suspect that's
not why you don't want to spend the $15. I would recommend a manual
as it's often difficult to read the markings and color codes on old
tantalums. Good luck.


--
Click to expand...

I found the manual at Qservice for $8 US. Operator and service manual. Two
gamma extenders would take will take about an hour to build up and you will
have them for the future. Or just remove the TM50x cover and you can reach
most anything. I doubt it is a shorted tantalum cap. More likely a switch or
pot that needs cleaning.

But I suspect the OP does not possess either the skill or desire to dig into
this. So he could just put the TM and the FG up on ebay and help cover the
cost of the non-repairable Chinese function generator. Also, good luck.
 
M

mike

You're willing to pay $400 for a replacement function generator, but
not $15 for a schematic to repair the one you currently own.

It's easy enough to calculate the relative cost of repair to replace.
My guess(tm) is that it would take me about 2 hrs and $20 in parts to
replace all the dip tantalum capacitors in the FG507. A little
Googling will show that old tantalums are a major problem in Tek
products. I value my spare time at $35/hr. That's $90 cost to repair
the FG507 without the risk of buying a manual from a questionable
source. Working blind does offer a challenge, but I suspect that's
not why you don't want to spend the $15. I would recommend a manual
as it's often difficult to read the markings and color codes on old
tantalums. Good luck.
Click to expand...
There are many well-meaning people who probably weren't even born
when the FG507 was designed. The current plague of bulging/open
computer/monitor caps simply does not apply to that era.
Yep, caps did fail, but ripping out all the caps probably won't
fix anything intermittent from that era.

A little history.
In the '70's, Tek used a LOT of teardrop tantalum caps. They were
very aware of the failure mode. The design guideline for tantalums
was changed to require significant voltage derating and an equivalent
resistance in series of something like 3 Ohms per volt...from memory...
That all but eliminated use of teardrop tantalum caps in new designs
by engineers who actually followed the guidelines. But there were a zillion
of them still in the field.

Tantalum caps have two modes. They work fine, or they're shorted.
That's not leaky, or a little bit shorted. They're DEAD shorted.
Once shorted, they never come back. I've never seen an intermittent
tantalum cap.
The short resistance is so low that it's difficult to get them hot...
but if you do have a HIGH current source, you can cause them to
explode. That's not an intermittent process either.

You can check most tantalum caps by poking an ohm-meter at 'em in circuit.
IF they're shorted, you can tell. It's rare to have a circuit resistance
low enough to mask the shorted tantalum cap.
 
C

Charles

"mike" wrote in message
Big snip.

I am pretty sure it's a gain problem perhaps related to a low supply
voltage. Once it started, it ran fine for days. When gain is on the hairy
edge, oscillators get iffy. They have trouble starting.

Nice people here, all trying to be helpful and I appreciate that.

Thanks Mike and thanks to all of you.
 
M

mike

in message
Big snip.

I am pretty sure it's a gain problem perhaps related to a low supply
voltage. Once it started, it ran fine for days. When gain is on the
hairy edge, oscillators get iffy. They have trouble starting.
Click to expand...

I've never seen the schematic, but I have done design reviews on
the FG501/2/3/4.
It's extremely likely that the oscillator is a cap with switched
current sources and threshold detectors determining the amplitude
of the triangle.
"Trouble starting" is likely not relevant.
You need to consult someone locally who knows how 1970's function
generators work...or do some googling. Well-meaning random inputs
from net denizens who don't have any relevant experience is often
counter-productive.

The FG507 topology is likely to be very similar to this:
http://bama.edebris.com/manuals/tek/fg503
with some sweep stuff bolted on.
The sweep is irrelevant except that it's possible for
one of the sweep tentacles to disable an otherwise working
triangle generator.
The components used to implement the circuit vary over time,
but the topology hasn't changed in decades.

This one is probably closer to the FG507 and worth downloading,
but understand the FG503 before
you delve into the complexity of the FG504. There's some stuff
in the 504 that is counter-intuitive and put there to patch up
some fundamental design flaws without a complete redesign.

http://bama.edebris.com/manuals/tek/fg504
 
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