bryce@zen.UUCP (09/17/87)
How to improve your Amiga 2000's video a lot and your Amiga 500's a little
(In three easy steps):
1> Trace the R G and B signals from the video connector back to three
ferrite beads. (Ferrite is a hard dark substance. The signals will be
run or looped through. There may be a component that looks like a ceramic
capacitor with three leads instead.)
2> Using a soldering iron, remove the three components.
3> Replace the gap with solid wire. (heavy gauge preferred)
|\ /| . Ack! (NAK, ENQ, SYN)
{o O} .
(") bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce
U How can you go back if you have not yet gone forth?netoprhm@ncsuvm.bitnet.UUCP (09/17/87)
The big question is -- Why (and how) does it work?
I would like some idea of what I am doing before I go munging
around in the innards of my brand new beige box.
Hal
NETOPRHM@NCSUVM.BITNET
bryce@hoser.berkeley.edu (Bryce Nesbitt) (09/19/87)
In article <169NETOPRHM@NCSUVM> NETOPRHM@NCSUVM.BITNET (Hal Meeks) writes: >The big question is -- Why (and how) does it work? >I would like some idea of what I am doing before I go munging >around in the innards of my brand new beige box. [read the referenced article to know what is going on] Ferrite beads are commonly used on output signals to attenuate higher frequency noise that might otherwise be radiated exte rnally to the computer. (Incurring the wrath of the Federal Crap-Cutters :-). Why ferrite was used on the *VIDEO* output is beyond me. I'll need to assume that for the A2000 it has something to do with the German version of the FCC, which has what I have heard are strict requirements. ( I don't know about that rumor... US companies always use the FCC as a scapegoat for late products. I've never heard this excuse used for a German design... so... ) In this case what the ferrite attenuates is part of the signal! On the A500 I have next to me it is (was) an in-line ferrite with one hole. The A2000 prototypes in town are the two hole, two loop type. That *really* does in a video signal. Why, again, I don't know. Even without the ferrite that connector is not going to radiate... it's connected to a shielded cable. My circa 1986 FCC docket is not clear if one must test with and without cables attached. If so, the solution is simple: add a 15 cent stamped metal end cap. An empty connector would be covered, a full one would have a shielded cable. Users would be instructed to use the cap or a cable. Mr. A2000 guy? |\ /| . Ack! (NAK, ENQ, SYN) {o O} . (") bryce@hoser.berkeley.EDU -or- ucbvax!hoser!bryce U How can you go back if you have not yet gone forth?
grr@cbmvax.UUCP (George Robbins) (09/29/87)
In article <3795@zen.berkeley.edu> bryce@hoser.berkeley.edu (Bryce Nesbitt) writes: > > How to improve your Amiga 2000's video a lot and your Amiga 500's a little > (In three easy steps): > > 1> Trace the R G and B signals from the video connector back to three > ferrite beads. (Ferrite is a hard dark substance. The signals will be > run or looped through. There may be a component that looks like a ceramic > capacitor with three leads instead.) > > 2> Using a soldering iron, remove the three components. > > 3> Replace the gap with solid wire. (heavy gauge preferred) Oops, the first few hundred A2000's had this little (but truly offensive, no?) problem with fuzzy video. The multi-turn ferrite beads were a little too effective - your dealer should have the info on how to fix this problem as part of warranty service. The A500 uses nice 1/2 turn beads. As far as I can tell, they have no visible effect on the video quality, even with a little a/b switch so that you can pop them in and out to check for subtle effects. -- George Robbins - now working for, uucp: {ihnp4|rutgers|allegra}!cbmvax!grr but no way officially representing arpa: out to lunch... Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)
grr@cbmvax.UUCP (George Robbins) (09/29/87)
In article <3822@zen.berkeley.edu> bryce@hoser.berkeley.edu.UUCP (Bryce Nesbitt) writes: > In article <169NETOPRHM@NCSUVM> NETOPRHM@NCSUVM.BITNET (Hal Meeks) writes: > >The big question is -- Why (and how) does it work? > >I would like some idea of what I am doing before I go munging > >around in the innards of my brand new beige box. > > [read the referenced article to know what is going on] > > Ferrite beads are commonly used on output signals to attenuate higher > frequency noise that might otherwise be radiated exte rnally to the > computer. (Incurring the wrath of the Federal Crap-Cutters :-). > > Why ferrite was used on the *VIDEO* output is beyond me. I'll need to > assume that for the A2000 it has something to do with the German version of > the FCC, which has what I have heard are strict requirements. ( I don't > know about that rumor... US companies always use the FCC as a scapegoat for > late products. I've never heard this excuse used for a German design... > so... ) Somehow, I don't think you've tried to get an entire system thru FCC lately. > Why, again, I don't know. Even without the ferrite that connector is not > going to radiate... it's connected to a shielded cable. My circa 1986 FCC > docket is not clear if one must test with and without cables attached. If > so, the solution is simple: add a 15 cent stamped metal end cap. An empty > connector would be covered, a full one would have a shielded cable. Users > would be instructed to use the cap or a cable. Uh, what goes in one end comes out the other, not to mention leakage from the less than 100% efficient shielding. The video output consists of more or less square edged pixels derived from the 7 MHz clock. This decomposes into useful video in the maybe 0-14 MHz range, and a bunch of higher order harmonics that exceed the bandwidth of the monitor, but tend to sneak out of the monitor or cable and into the FCC test receiver. This effect is worse when the monitor is separatly powered and thus has multiple ground paths. Properly chosen the ferrite beads work magic and chop the bad stuff without perceptible effect on the video. Current FCC test requirements specify that the device be tested in a system configuration. That is if you sell a monitor/modem/printer it must be tested with these devices attached. It must also pass with any arbitrary positioning of components and cables. Doens't matter that the user normally doesn't wrap his mouse cable in a snake coil and leave it lying on the keyboard. -- George Robbins - now working for, uucp: {ihnp4|rutgers|allegra}!cbmvax!grr but no way officially representing arpa: out to lunch... Commodore, Engineering Department fone: 215-431-9255 (only by moonlite)