FG 504 Offset problem


 

Dear All,
The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
I thought this would be an easy fix, but I am about to quit.
In case someone gets interested, I have uploaded this section of the schematics.
First, I checked the + and - 15V and the +/- 4V input and they are ok.
Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
With these transistors out of circuit, the output of U-1145 goes from
-13V to + 7.0V.
I ran out of ideas.
I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
Any suggestions?
Thank you


Dave Casey <dcasey@...>
 

You made no mention of the +/- 25V supplies. Have you checked these?
 
Dave Casey
Sent from my PC

----- Original Message -----
From: gehp01
Sent: Saturday, August 28, 2010 4:16 PM
Subject: [TekScopes] FG 504 Offset problem

 

Dear All,
The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
I thought this would be an easy fix, but I am about to quit.
In case someone gets interested, I have uploaded this section of the schematics.
First, I checked the + and - 15V and the +/- 4V input and they are ok.
Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
With these transistors out of circuit, the output of U-1145 goes from
-13V to + 7.0V.
I ran out of ideas.
I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
Any suggestions?
Thank you


Tom Miller <tmiller@...>
 

Do you have the +/- 25 volts? What is on pin 2 of the amp? Can you set that to 0 volts
with R1140? The +7 at pin 6 sounds bad if pin 2 is near 0 volts. What about Q1160
and 1180. Are they ok? Check R1160 and 1180.
 
Regards,
Tom
 
 

----- Original Message -----
From: gehp01
Sent: Saturday, August 28, 2010 5:16 PM
Subject: [TekScopes] FG 504 Offset problem

 

Dear All,
The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
I thought this would be an easy fix, but I am about to quit.
In case someone gets interested, I have uploaded this section of the schematics.
First, I checked the + and - 15V and the +/- 4V input and they are ok.
Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
With these transistors out of circuit, the output of U-1145 goes from
-13V to + 7.0V.
I ran out of ideas.
I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
Any suggestions?
Thank you


 

Folks,
Thank you for your replies.
First, I have to correct my first post:
I pulled out Q1150 and Q1160. Q1170 is still on the board.
Also, I forgot to mention that the +/- 25V are also OK.
According to the suggestions, I checked R1160 and R1180 and they are fine.
The voltage on Pin 2 varies from -17mV to about +3.0V, at the two extremes of offset adjustment,R1130.
I have not checked Q1170 and Q1180 because the negative offset is working fine, even with Q1150 and Q 1180 out of circuit.
I have been thinking about trying to replace U1145 from the top of the board, using my dessoldering gun (vaccum type).
I used that to remove Q1150 and Q1160 and it worked fine, but transistors are much more easier to dessolder that IC's.
Does anybody ever tried that?
I am afraid of damaging the board or get stuck with a overheated IC still stuck in place.
Thanks,
Roger

--- In TekScopes@..., "Tom Miller" <tmiller@...> wrote:

Do you have the +/- 25 volts? What is on pin 2 of the amp? Can you set that to 0 volts
with R1140? The +7 at pin 6 sounds bad if pin 2 is near 0 volts. What about Q1160
and 1180. Are they ok? Check R1160 and 1180.

Regards,
Tom


----- Original Message -----
From: gehp01
To: TekScopes@...
Sent: Saturday, August 28, 2010 5:16 PM
Subject: [TekScopes] FG 504 Offset problem



Dear All,
The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
I thought this would be an easy fix, but I am about to quit.
In case someone gets interested, I have uploaded this section of the schematics.
First, I checked the + and - 15V and the +/- 4V input and they are ok.
Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
With these transistors out of circuit, the output of U-1145 goes from
-13V to + 7.0V.
I ran out of ideas.
I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
Any suggestions?
Thank you


Artekmedia <manuals@...>
 

Roger
The best approach IMO for removing IC's from a thru-hole PCB is to take a small pair of cutters clip the IC out lead by lead and then use your desoldering iron to remove the lead ends from the holes...hard to "salvage" the IC this way is the only down side,
Dave

On 8/29/2010 6:54 AM, gehp01 wrote:
 



Folks,
Thank you for your replies.
First, I have to correct my first post:
I pulled out Q1150 and Q1160. Q1170 is still on the board.
Also, I forgot to mention that the +/- 25V are also OK.
According to the suggestions, I checked R1160 and R1180 and they are fine.
The voltage on Pin 2 varies from -17mV to about +3.0V, at the two extremes of offset adjustment,R1130.
I have not checked Q1170 and Q1180 because the negative offset is working fine, even with Q1150 and Q 1180 out of circuit.
I have been thinking about trying to replace U1145 from the top of the board, using my dessoldering gun (vaccum type).
I used that to remove Q1150 and Q1160 and it worked fine, but transistors are much more easier to dessolder that IC's.
Does anybody ever tried that?
I am afraid of damaging the board or get stuck with a overheated IC still stuck in place.
Thanks,
Roger

--- In TekScopes@..., "Tom Miller" wrote:
>
> Do you have the +/- 25 volts? What is on pin 2 of the amp? Can you set that to 0 volts
> with R1140? The +7 at pin 6 sounds bad if pin 2 is near 0 volts. What about Q1160
> and 1180. Are they ok? Check R1160 and 1180.
>
> Regards,
> Tom
>
>
> ----- Original Message -----
> From: gehp01
> To: TekScopes@...
> Sent: Saturday, August 28, 2010 5:16 PM
> Subject: [TekScopes] FG 504 Offset problem
>
>
>
> Dear All,
> The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
> I thought this would be an easy fix, but I am about to quit.
> In case someone gets interested, I have uploaded this section of the schematics.
> First, I checked the + and - 15V and the +/- 4V input and they are ok.
> Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
> With these transistors out of circuit, the output of U-1145 goes from
> -13V to + 7.0V.
> I ran out of ideas.
> I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
> Any suggestions?
> Thank you
>


-- 
Dave & Lynn Henderson
Manuals@...
www.Artekmedia.com
PO Box 175
Welch,MN 55089


Jerry Massengale <jmassen418@...>
 

Hi,
 
I use my vacuum desoldering gun when removing ICs. I make sure the gun is cleaning and drawing good and makes sure I have the solder flowing before I trigger. I move the tip in a tight circular motion to get all sides of the lead. I then inspect to find any remaining solder. I then use solder braid to remove any remaining solder. I then gently jiggle the lead to insure it is free. When every lead is free to move, I ply the IC out with a small pair of tweezers. Never force. If I cannot free a lead gently, I resolder the lead and try to remove all the solder again. If I fail again, I use a special pair of diagonal cutters to clip the IC at the body and then remove the stuck lead. I rarely ever have to destroy the IC. As long as you do not use pressure against the etch pad, it should be okay. I watch the fiberglass material for freckling around the pad. If I see that, I back off and quit trying to save the IC. TTL chips like the 7402 and 741 op amp are very cheap and replaceable. I do not hesitate to sacrifice those. Tektronix house chips, I try to save.
 
Jerry


--- On Sun, 8/29/10, Artekmedia wrote:

From: Artekmedia
Subject: Re: [TekScopes] Re: FG 504 Offset problem
To: TekScopes@...
Date: Sunday, August 29, 2010, 7:15 AM

 
Roger
The best approach IMO for removing IC's from a thru-hole PCB is to take a small pair of cutters clip the IC out lead by lead and then use your desoldering iron to remove the lead ends from the holes...hard to "salvage" the IC this way is the only down side,
Dave

On 8/29/2010 6:54 AM, gehp01 wrote:
 


Folks,
Thank you for your replies.
First, I have to correct my first post:
I pulled out Q1150 and Q1160. Q1170 is still on the board.
Also, I forgot to mention that the +/- 25V are also OK.
According to the suggestions, I checked R1160 and R1180 and they are fine.
The voltage on Pin 2 varies from -17mV to about +3.0V, at the two extremes of offset adjustment,R1130.
I have not checked Q1170 and Q1180 because the negative offset is working fine, even with Q1150 and Q 1180 out of circuit.
I have been thinking about trying to replace U1145 from the top of the board, using my dessoldering gun (vaccum type).
I used that to remove Q1150 and Q1160 and it worked fine, but transistors are much more easier to dessolder that IC's.
Does anybody ever tried that?
I am afraid of damaging the board or get stuck with a overheated IC still stuck in place.
Thanks,
Roger

--- In TekScopes@..., "Tom Miller" wrote:
>
> Do you have the +/- 25 volts? What is on pin 2 of the amp? Can you set that to 0 volts
> with R1140? The +7 at pin 6 sounds bad if pin 2 is near 0 volts. What about Q1160
> and 1180. Are they ok? Check R1160 and 1180.
>
> Regards,
> Tom
>
>
> ----- Original Message -----
> From: gehp01
> To: TekScopes@...
> Sent: Saturday, August 28, 2010 5:16 PM
> Subject: [TekScopes] FG 504 Offset problem
>
>
>
> Dear All,
> The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
> I thought this would be an easy fix, but I am about to quit.
> In case someone gets interested, I have uploaded this section of the schematics.
> First, I checked the + and - 15V and the +/- 4V input and they are ok.
> Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
> With these transistors out of circuit, the output of U-1145 goes from
> -13V to + 7.0V.
> I ran out of ideas.
> I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
> Any suggestions?
> Thank you
>


--
Dave & Lynn Henderson
Manuals@...
www.Artekmedia.com
PO Box 175
Welch,MN 55089


Alexandre Souza - Listas <pu1bzz.listas@...>
 

The best approach IMO for removing IC's from a thru-hole PCB is to take
a small pair of cutters clip the IC out lead by lead and then use your
desoldering iron to remove the lead ends from the holes...hard to
"salvage" the IC this way is the only down side,
Dave, I can remove any IC using my trustworthy weller soldering station and a common solder sucker pump. It is just a matter of learning how to do.

I'm planing in buying a mini-dv camera (as soon as some $$$ appears miraculosely on my wallet) and will create some tutorials for my page (http://www.tabalabs.com.br), this will be one of these :)


stefan_trethan
 

This method must be good since we have independently arrived at exactly the same thing, especially the circular motion seems to be the key, as well as triggering the vacuum only when the solder has molten through.

Meanwhile I have put many hours on my ZD 915 desoldering station:
<http://www.komerci.de/shop/images/produktbilder/entloetstation_zd-915.jpg>

I use it many times every day and it is switched on 8 hours a day. So far it has given me no trouble at all, in two or three months of using it.

There is only one thing I would recommend, and that is fitting a more powerful supply for the vacuum motor. It is driven by the same transformer as the heater and does not run anywhere near full capacity. I fitted a 15V 60W switchmode supply, which seems about the ideal voltage. Also one must make sure to get the new and improved model with a black plastic insert attaching the heater barrel to the gun rather than the old model without that, which tends to fail at this point.

Amazingly this tool hasn't really clogged even once, when the DENON SC-7000 gives us much trouble in that regard. I never expected that from a 50eur tool (compared to 350eur for the DENON). The tips wear out faster than those of the DENON, but are only just over 1eur compared to 40eur for the DENON. I think HAKKO tips would fit, since this is a copy, and those may have better plating (but again cost more).

I've bought the same station for my home shop and three more units for work since people kept annoying me to desolder stuff for them. Even if it breaks tomorrow (and can't be fixed) I'd buy another and still consider it good value for money.

Anyway, sorry for the off topic, but if you have any serious desoldering needs a desoldering iron is a must, braid or a manual solder sucker just doesn't compare. I'm glad I have finally found an affordable unit that works, and works better than the expensive ones.


ST







On Sun, Aug 29, 2010 at 2:50 PM, Jerry Massengale <jmassen418@...> wrote:


Hi,
 
I use my vacuum desoldering gun when removing ICs. I make sure the gun is cleaning and drawing good and makes sure I have the solder flowing before I trigger. I move the tip in a tight circular motion to get all sides of the lead. I then inspect to find any remaining solder.
...
 
I then gently jiggle the lead to insure it is free


Tom Miller <tmiller@...>
 

LM 301 op amps are cheap and available. Just do as Dave suggested and clip all the
leads off near the can. Then remove each lead one at a time and clean up the holes.
You can then solder in a new chip from the top.
 
The fact that pin 2 is not symmetrical about 0 volts says that the IC is most likely bad.
Are the two 10 K resistors ok?
 
Regards,
Tom
 
 
 
 
 

----- Original Message -----
From: gehp01
Sent: Sunday, August 29, 2010 7:54 AM
Subject: [TekScopes] Re: FG 504 Offset problem

 



Folks,
Thank you for your replies.
First, I have to correct my first post:
I pulled out Q1150 and Q1160. Q1170 is still on the board.
Also, I forgot to mention that the +/- 25V are also OK.
According to the suggestions, I checked R1160 and R1180 and they are fine.
The voltage on Pin 2 varies from -17mV to about +3.0V, at the two extremes of offset adjustment,R1130.
I have not checked Q1170 and Q1180 because the negative offset is working fine, even with Q1150 and Q 1180 out of circuit.
I have been thinking about trying to replace U1145 from the top of the board, using my dessoldering gun (vaccum type).
I used that to remove Q1150 and Q1160 and it worked fine, but transistors are much more easier to dessolder that IC's.
Does anybody ever tried that?
I am afraid of damaging the board or get stuck with a overheated IC still stuck in place.
Thanks,
Roger

--- In TekScopes@..., "Tom Miller" wrote:
>
> Do you have the +/- 25 volts? What is on pin 2 of the amp? Can you set that to 0 volts
> with R1140? The +7 at pin 6 sounds bad if pin 2 is near 0 volts. What about Q1160
> and 1180. Are they ok? Check R1160 and 1180.
>
> Regards,
> Tom
>
>
> ----- Original Message -----
> From: gehp01
> To: TekScopes@...
> Sent: Saturday, August 28, 2010 5:16 PM
> Subject: [TekScopes] FG 504 Offset problem
>
>
>
> Dear All,
> The positive side of the DC offset of my FG-504 is not working, but negative is working fine.
> I thought this would be an easy fix, but I am about to quit.
> In case someone gets interested, I have uploaded this section of the schematics.
> First, I checked the + and - 15V and the +/- 4V input and they are ok.
> Next, I pulled out Q-1150 and Q-1170 and, to my surprize, both are ok also.
> With these transistors out of circuit, the output of U-1145 goes from
> -13V to + 7.0V.
> I ran out of ideas.
> I would not venture to replace U1145 since this would mean to disassemble almost the entire unit.
> Any suggestions?
> Thank you
>


Tom Miller <tmiller@...>
 

Hi Stefan,
 
That unit looks nice. Is it available for 120 VAC 60 Hz?.
 
How can I get one in the USA?
 
 
Thanks,
Tom
 

----- Original Message -----
Sent: Sunday, August 29, 2010 10:26 AM
Subject: Re: [TekScopes] Re: FG 504 Offset problem

 

This method must be good since we have independently arrived at exactly the same thing, especially the circular motion seems to be the key, as well as triggering the vacuum only when the solder has molten through.

Meanwhile I have put many hours on my ZD 915 desoldering station:
<http://www.komerci.de/shop/images/produktbilder/entloetstation_zd-915.jpg>

I use it many times every day and it is switched on 8 hours a day. So far it has given me no trouble at all, in two or three months of using it.




stefan_trethan
 

It is available for 120V:
<http://www.china-zhongdi.com/zd-915.htm>

I have no idea how to get it in the US. Here in europe it is available from Farnell under no. 1498361, I expect you can get if from Newark as well. But of course Farnell has the usual double price compared to the cheap importers like komerci.de.

Perhaps you can find it with google or on ebay?

Just mind that you get the new model with the black plastic ring attaching the heater, many places still have the old photo so ask to make sure you get the current one.

I suspect it is easy to modify a 230V unit to 120V, likely the transformer just needs re-wiring. If you can only find a source for 230V models I can have a look for you to check if this is possible.

ST

On Sun, Aug 29, 2010 at 4:56 PM, Tom Miller <tmiller@...> wrote:



Hi Stefan,
 
That unit looks nice. Is it available for 120 VAC 60 Hz?.
 
How can I get one in the USA?
 
 
Thanks,
Tom



Artekmedia <manuals@...>
 

Oh I can too ..... and have, as a manufacturing engineer at Motorola back in the 70's I was trained by some of the most skilled repair gals from the production line on handie-talkies and pagers with much denser and more delicate boards than a typical 500 series plug-in , lots of flux, a pinch of extra solder and a rubber sucking bulb with a Teflon tip  .....but for common garden variety IC's why put a 30 year old PCB at risk?

Dave



On 8/29/2010 8:03 AM, Alexandre Souza - Listas wrote:
 

> The best approach IMO for removing IC's from a thru-hole PCB is to take
> a small pair of cutters clip the IC out lead by lead and then use your
> desoldering iron to remove the lead ends from the holes...hard to
> "salvage" the IC this way is the only down side,

Dave, I can remove any IC using my trustworthy weller soldering station
and a common solder sucker pump. It is just a matter of learning how to do.

I'm planing in buying a mini-dv camera (as soon as some $$$ appears
miraculosely on my wallet) and will create some tutorials for my page
(http://www.tabalabs.com.br), this will be one of these :)


-- 
Dave & Lynn Henderson
Manuals@...
www.Artekmedia.com
PO Box 175
Welch,MN 55089


Glenn Little
 

These are all techniques described by PACE in their desoldering information.
The also define the proper desoldering tip based on lead size and pad size.

I think that PACE developed the desoldering tools and the many copies followed.

After building my own desoldering station many years ago, I now use and older PACE system with no regrets.

73
Glenn
WB4UIV

At 10:26 AM 8/29/2010, you wrote:


This method must be good since we have independently arrived at exactly the same thing, especially the circular motion seems to be the key, as well as triggering the vacuum only when the solder has molten through.


On Sun, Aug 29, 2010 at 2:50 PM, Jerry Massengale <jmassen418@...> wrote:


Hi,
 
I use my vacuum desoldering gun when removing ICs. I make sure the gun is cleaning and drawing good and makes sure I have the solder flowing before I trigger. I move the tip in a tight circular motion to get all sides of the lead. I then inspect to find any remaining solder.

...
 
I then gently jiggle the lead to insure it is free


casy_ch@tbwil.ch
 

Hi Dave
 
I did not know that you have or are involved in "gardens" - hi
 
Vy 73
Jean-Claude
 
 

----- Original Message -----
From: Artekmedia
Sent: Sunday, August 29, 2010 5:02 PM
Subject: Re: [TekScopes] Re: FG 504 Offset problem

 

Oh I can too ..... and have, as a manufacturing engineer at Motorola back in the 70's I was trained by some of the most skilled repair gals from the production line on handie-talkies and pagers with much denser and more delicate boards than a typical 500 series plug-in , lots of flux, a pinch of extra solder and a rubber sucking bulb with a Teflon tip  .....but for common garden variety IC's why put a 30 year old PCB at risk?

Dave



On 8/29/2010 8:03 AM, Alexandre Souza - Listas wrote:

 

> The best approach IMO for removing IC's from a thru-hole PCB is to take
> a small pair of cutters clip the IC out lead by lead and then use your
> desoldering iron to remove the lead ends from the holes...hard to
> "salvage" the IC this way is the only down side,

Dave, I can remove any IC using my trustworthy weller soldering station
and a common solder sucker pump. It is just a matter of learning how to do.

I'm planing in buying a mini-dv camera (as soon as some $$$ appears
miraculosely on my wallet) and will create some tutorials for my page
(http://www.tabalabs.com.br), this will be one of these :)


--
Dave & Lynn Henderson
Manuals@...
www.Artekmedia.com
PO Box 175
Welch,MN 55089