Shields on or off?

[J-Data]

So I just replaced the RAM in my console and to save time, I didn't replace the main board top and bottom shields when I put the unit back together.  It worked fine, and I didn't notice any change, good or bad on the audio or the video signals.  So, whats the prevailing thought, keep the shields or ditch 'em?

[+arcadeshopper]

Ditch them but you need a heatsink for your VDP if it's an older style motherboard so you might want to put it back on just for the heat sink

 

Sent from my LM-G820 using Tapatalk

 

 

 

 

[J-Data]

OK, I'll add a stick on heat-sink on the TMS9918A.  I'll bet allowing direct airflow over the board without the shield will generally improve the system thermals but obviously some parts need more.  The max power on some of theses old school TTL parts are ridiculously high. 

[GDMike]

 Think the shielding was just part of the strict RF rules that computer mnfctrs had to obey by.

[matthew180]

It was a big expense for TI to include them for sure, and probably required to pass RF certifications for home use, as previously mentioned.  As you have discovered the 99/4A seems to run fine without them, but that is not true for all computers that use shields (not replacing shields should not be considered a universal truth), so be mindful.  Personally I put mine back on for a few reasons:

 

* The lower shield provides the fingered shield-coupling for side-port connections, like the PEB cable.  Shields are very important in cables.

 

* The upper shield provides a physical support for the cartridge-port angle connector, although the upper half of the case does too.

 

* The shields protect in both directions, i.e. they also shield the motherboard *from* external noise.

 

* I find the motherboard fits better with at least the lower shield in place.

 

* TI included them (probably) because they were needed to pass testing, which means the 99/4A is probably a very noisy RF system.  With all the WiFi, Bluetooth, cell phones, etc. being used today, I don't need another source of electromagnetic noise if I can help it.  My 99/4A sits in close proximity to a lot of other computers on my bench, and I don't want some other wireless device acting flaky because the 99/4A is unknowingly throwing off interference.

 

Anyway, just my take on it.  If you do install either half of the shield, make sure you secure it with at least two screws on either end of the motherboard!  If the shield is misaligned even a little it can short other signals and voltages and possibly let the smoke out of your motherboard or power supply.

[GDMike]

I hear every bit passing through to my flatscreen sitting on top of my peb.

I have to turn the volume down, and just like that it's quiet again..

But yup, I always put those shields back in my Console after I have pulled it apart for some reason, then i get bent out of place because I put the screws and nuts on upside down.

I had heard at some point in my life that airflow has its way of working through it as well. And at one point I thought about putting a little fan in it, but, shoot I might cause more harm than good, AND knock on wood, all three consoles are still operational, but one could use a video chip replacement. 

ML

 

Edited March 24, 2020 by GDMike

[Ed in SoDak]

The RF interference would hit AM radios and analog TV hardest. Many TVs still used the old flat twin lead antenna wire which offered zero shielding. These days the FCC could give a hoot about AM and RF noise, damn-near every gadget and wallwart broadcasts radio hash to some extent, some can be severe.

 

For cooling, a small computer fan placed on top of the console vent behind the cart port works wonders. Mine runs off a low-voltage wallwart, it's still effective at reduced speed and not loud at all.

-Ed

[hhos]

Does the QI version even have shields?  It seems to me that it does not.  If my memory serves, the 9918A has some sort of spring metal heat sink attached to it.  I have a few of those consoles.  I will have to take a look later.  If someone else beats me to it, that's even better.

 

HH

[+Lee Stewart]

I seem to recall that the QI version has a prayed-on metal coating on the inside of the clamshell.

 

...lee

[Stuart]

12 hours ago, Lee Stewart said:

I seem to recall that the QI version has a prayed-on metal coating on the inside of the clamshell.

Our Father who art in Heaven,

Please let my QI TI work,

Without undue RF interference,

...

 

 

 

[JB]

On 3/23/2020 at 1:35 PM, matthew180 said:

TI included them (probably) because they were needed to pass testing, which means the 99/4A is probably a very noisy RF system. 

FCC regulations at the time where much stricter than they are now. I'd wager the 4a is pretty quiet by modern standards.

[hhos]

I think almost all the home computers of the '80s were pretty quiet RF-wise.  The Model 1 TRS-80 was pretty bad, but it was late 70s.  I think the expansion box was pretty bad, too.

On 3/24/2020 at 4:17 AM, Lee Stewart said:

I seem to recall that the QI version has a prayed-on metal coating on the inside of the clamshell.

 

...lee

I can't seem to locate any of my QIs.  I am sure I had either 3, or 5, of them, but since I can't find them, I can't check this out.