8mm Forum: GS1200 Capacitor Swap Help!

This is topic GS1200 Capacitor Swap Help! in forum 8mm Forum at 8mm Forum.

To visit this topic, use this URL:
https://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=012735

Posted by Burton Sundquist (Member # 5813) on January 23, 2019, 08:15 PM:

I installed a new capacitor to replace the original C172 in my GS1200. As careful as I was it looks like I have created 2 solder bridges. Looking at the back of the board, where the top terminal is, solder is touching the terminal to it's right.
These two points appear to be part of one printed circuit but need advice. The same thing happened at the bottom terminal.
solder is touching the terminal beside it to the right. These terminals appear to be part of another printed circuit. I would appreciate advice on this.

[ January 23, 2019, 09:32 PM: Message edited by: Burton Sundquist ]

Posted by Burton Sundquist (Member # 5813) on January 25, 2019, 08:25 PM:

...Anyone? I tried to de-solder it but there is still a trace of solder connecting the top capacitor terminal to the terminal on its right. Same on the bottom.

[ January 25, 2019, 10:37 PM: Message edited by: Burton Sundquist ]

Posted by Graham Ritchie (Member # 559) on January 26, 2019, 03:41 AM:

Burton

You need to buy a "de-soldering pump" they are cheap to buy at most electronics suppliers . Can you post some photos? If in any doubt about soldering, I would suggest finding someone to do it for you. If not be very careful not to apply heat in any one spot for to long.

Posted by Burton Sundquist (Member # 5813) on January 27, 2019, 12:43 AM:

Graham, So happy to hear from you and Thanks for replying. Terrible photo just like the soldering job. I sucked up the extra solder that made the bridge but there is
No way of getting rid of the trail from the top capacitor post to the other terminal. To me it looks like it should be part of the same circuit? Or am I out to lunch ( stupid ). Same with the bottom solder. looks like another blunder. I wlll try once more heading your advice about overheating the board. Thanks again.

Posted by Phil Murat (Member # 5148) on January 27, 2019, 05:19 AM:

Hi Burton,
I suggest you to use small soldering wire, 1mm diam, special electronic with resin included.
To prevent from sensible components overheat' maxi soldering time is approx 3 to 5 sec.
Soldering iron with narrow tip showing 20 w is ok, 10w with batterie is good for soldering chips or very sensible components.
a solder is considered to be satisfactory when it appears shinny and well collapsed. A ball appearance is not good.

As Graham said, a desoldering pump is a necessary investment. I use also Copper mesh depending on the situation.

Is it possible to get more picture(s) for board concerned ?
If board is epoxy, this is a good news, as epoxy boards are stronger than former plastic or bakelite ones. Epoxy board are fibers reinforced.

What is the function of this board stage ?
Why did this capacitor failed (aging or overheat) ?

Try to train on scrapped electronic board showing different kinds of components to be more confident with that.
However, fusion soldering point on modern bords is higher than vintage assemblies

Let us know
Thanks

Posted by Leon Norris (Member # 3151) on January 27, 2019, 02:20 PM:

Don't worry Burt Because I have a few in stock! Just take your time. The amp assy. Comes in two parts! Hopefully you will do good. But if not then let me know! Thanks, Leon.

Posted by Burton Sundquist (Member # 5813) on January 27, 2019, 02:57 PM:

Thanks fellows, but the original question I have has not been answered. At the top, is the capacitor terminal supposed to be connected via printed portion to the terminal to its right?
Same question re: the bottom Capacitor terminal. Anyone with electrical knowledge of this board? Thanks...

Posted by Leon Norris (Member # 3151) on January 27, 2019, 03:18 PM:

What you need Burt is a good Desoldering tool. Like I got! Its a electric one. Its very strong. It sucks up that old solder in seconds! It does a great job! Good luck! Leon.

Posted by Renzo Dal Bo (Member # 5688) on January 27, 2019, 03:20 PM:

Hi Burton,
maybe this thread can help you.

http://8mmforum.film-tech.com/cgi-bin/ubb/ultimatebb.cgi?ubb=get_topic;f=1;t=007889#000000

The capacitor is only a "bridge" connecting the two largest top right "islands" of the PCB and it hasn't any polarity to respect.

Posted by Burton Sundquist (Member # 5813) on January 27, 2019, 08:48 PM:

Thanks Renzo, Leon, Phil and Graham for all your Help. Board cleaned up and joints re-soldered. Test recorded and I know have full dynamic range on both tracks! I never knew such small stripes could produce audio of this Quality! Thanks again to everyone!

Posted by Paul Adsett (Member # 25) on January 27, 2019, 10:17 PM:

Congratulations Burton. Any time and energy that you spent on this modification will be well worth it when you listen to that stellar quality stereo!
I have yet to do this mod on my GS's, since I use my Eumig S938 Stereo for all re-recording jobs, but I really ought to take it on and get my GS up to full specs and performance. Exactly what capacitor did you use and where did you get it?

Posted by Burton Sundquist (Member # 5813) on January 28, 2019, 12:29 AM:

Hi Paul, Yes if you have the right tools for the task and work carefully it's a simple replacement and that is it. If need be you could also adjust the bias for each channel after swapping the capacitor. Not needed in my case as both tracks are in balance and produce full range.
Here is a link for the capacitor I used:

https://w ww.ebay.ca/itm/1pcs-PHILIPS-KS-3300P-3300pF-3-3nF-630V-1-Axial-Polystyrene-Capacitor/151664766262?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m1438.l2649

...This was courtesy of Renzo. His sync box works excellent as I already synced a
DVD almost frame to frame on 800' reel. The sound is so amazing, particularly the balance stripe considering it's width.

And Phil, I wanted to answer your questions too. This capacitor is a recording component on the amplifier board
Known to fail after many years due to its proximity to a resister that heats up during recording. Some members have replaced the capacitor on the back side of the board for this reason. Thanks to everyone who was of help!

Posted by Phil Murat (Member # 5148) on January 28, 2019, 04:05 AM:

Thanks Burton for this info.

So, I have not replaced this capacitor on my machines yet.

However I understand this capacitor is working under high frequencies so that it overheats.

If there is room enough around preamp board I will not installed the same capacitor (3000pf / 630V , polystyrene),but I'll replace it by 2 x 1500pf or 3 x 1000pf installed in parallel to decrease impedance.(Polyester or polypropilene caps are supposed to work too).
By this way overheating has to decrease significantly.

UBB.classic^TM 6.3.1.2