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avatar_WacKEDmaN

Jumpy screen with GBS-8200

Started by WacKEDmaN, 05:44, 24 December 22

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WacKEDmaN

#25
i am noticing some current draw through the CPC when off with the GBS powered by a wall wart...but its nowhere near as bad (60mA)  as with the PC PSU powering both (upto 200mA)... and theres no bounce...

Bryce

What needs to be understood is that you are connecting an 80's (relatively) low frequency device with pretty much no filtering for modern SMPSU's together with a modern device that has filtering for itself, but may mess up the power rails with spikes both from itself, but also probably reflecting the spikes from the PSU back at the CPC. My suggestion would be to add adequate filtering (perhaps a 100uH inductor (in series), a hefty 470uf Capacitor and a 100nf ceramic capacitor (in parallel)) between the GBS and the CPC. This will most likely remove all issues.

Bryce.

WacKEDmaN

#27
Quote from: Bryce on 19:27, 30 December 22What needs to be understood is that you are connecting an 80's (relatively) low frequency device with pretty much no filtering for modern SMPSU's together with a modern device that has filtering for itself, but may mess up the power rails with spikes both from itself, but also probably reflecting the spikes from the PSU back at the CPC. My suggestion would be to add adequate filtering (perhaps a 100uH inductor (in series), a hefty 470uf Capacitor and a 100nf ceramic capacitor (in parallel)) between the GBS and the CPC. This will most likely remove all issues.

Bryce.
where exactly "between" the cpc and gbs? i mean theres only RGBS+GND out of the cpc to the gbs..

...and do you reckon i could maybe get away with another buck (that has chunky inductor and caps) on the gbs..that should provide some filtering, just as the buck on the cpc is...

eto

Quote from: WacKEDmaN on 01:39, 30 December 22you can see here in this video clip...

https://youtube.com/clip/UgkxcPZgvmHbz_9v37zRzVvl2FXQrpyAFP5B
That one I experience too! 

@Bryce could you maybe give more details about the filter? I'd love to try that out. 

Bryce

This: Hand drawn because someone recently said they wanted to see how shitty my hand drawn circuits look like :)

Bryce.


WacKEDmaN

Quote from: Bryce on 13:56, 31 December 22This: Hand drawn because someone recently said they wanted to see how shitty my hand drawn circuits look like :)

Bryce.


not so shitty!...
..so i guess that on both cpc and gbs... like i said i thought the buck on the CPC would be providing some filtering.. ill have to give it a go with another buck (just with voltage display) on the gbs and see how it goes..
if i still have issues ill have to source some bits from old boards n make up a filter or 2...

i guess we really need to design a nice 5v and 12v power supply with the filtering built in... (but i would think a proper lab bench power supply from a reputable brand like siglent would already have adiqite filtering..yet we still see the issue)

Bryce

Not only does a buck NOT filter, it introduces more noise due to its switching frequency.

Is the Siglent a switched mode PSU or linear?

Bryce.

WacKEDmaN

not sure...id have to go through mates videos to find out... siglent or rigol.. one of the two!

eto

Quote from: Bryce on 13:56, 31 December 22This: Hand drawn because someone recently said they wanted to see how shitty my hand drawn circuits look like :)
Thanks a lot. I just ordered the inductor and will give that a try once it arrives.

Would that then be a recommended set-up any time we are connecting the CPC to e.g. a PC power supply or only in those cases, when someone wants to connect a modern device like the GBS in parallel? 

Bryce

Yes, that's the bit that's missing in Retro hardware, that would make them more compatible with SMPSU's.

Bryce.

WacKEDmaN

im gonna source some components off old boards tomorrow and build a couple of them up for both the 12v and 5v rails coming from the PC PSU...

hopefully that sorts the issue.... 
no offence Bryce  (yeah yeah another silly idea!)...
but i dont see how a filter like this will stop the current flow through the CPC when its off.....sure it will smooth spikes or drops..but i dont see how it can stop that current flow....
can you please explain how Bryce?!... or link somewhere with some good (easy to comprehend!) articles plz....

Bryce

It definitely won't stop current from flowing through the CPC, but that current isn't a problem it's a requirement for the monitor to work. Turn your PC monitor on and leave the PC off, you'll see current flowing too. The monitor needs to sense what's connected to it and that would be impossible with no current.

Bryce.

WacKEDmaN

#37
Quote from: Bryce on 12:38, 02 January 23It definitely won't stop current from flowing through the CPC, but that current isn't a problem it's a requirement for the monitor to work. Turn your PC monitor on and leave the PC off, you'll see current flowing too. The monitor needs to sense what's connected to it and that would be impossible with no current.

Bryce.
i didnt think it would be able to stop it!....

but....it SHOULD NOT be flowing through the CPC.... it should only be on the GBS that the monitor detect is on... i mean the input side (that the CPC is on) shouldnt matter, the GBS detects the sync... not the power....(eg pulling the CPC RGBS from the GBS still lets the monitor connected to it display)
looking at the CPC schematic.. i cant see how current can be flowing.. i see RGB is pulled up to 5v..but there should be no 5v with it off!... and it shouldnt be connected anywhere that will it flow.... can you see the path on the schematic Bryce? (remember..LUM is not connected!)

i might hook up my PC monitor that works direct from CPC again and check the current...im fairly sure i didnt see any when the CPC was off..
i dont see how current can be flowing on RGB+S pins.. they are all "logic".. so should have very little current, and the chips aint powered so there should be no current...

maybe all i really need to do is put the GBS power AFTER the CPC switch (and add the filtering).... so switching the CPC off also switches the GBS off and kills that current flow! (i really dont like the thought of current flowing through the GA when its off)..
...but then my buck/meter will show current draw of both CPC and GBS which i dont really want!
...or do away with the CPC switch and put in a switch via the CPCs incoming power rail...(so no current can flow into the CPC to begin with!)

EDIT: i wonder if i should break out the scope and have a probe around with the CPC off and see exactly where that current is flowing....

Bryce

The GBS also needs to detect the inputs, so the RGB pins of the GBS would have some voltage present that could be flowing through the Gate Array.

Bryce.

WacKEDmaN

#39
thanks Bryce.. i know it seems like we going around in circles here... but im just trying to get my head around how its happening!.. again, really do appreciate the help! (and i know eto does too!)

bugga...im gonna have to wait till the weekend for the filter...
you think i can find any 'marked' inductors on any of my old boards n power supplies?!
and i dont have a LCR meter or function gen to test the values.. its too long winded, and too much setup to test them with a scope and or multimeter!..ill just have to wait! (coz im a lazy ass!)

do you know where id definitely find a 100uH on a board Bryce? (anythin like old mobos, network cards, PSUs etc etc)...does the 100uH matter? can it be say 220uH? (i think i found some marked 220...not entirely sure what they actually are tbh! they got a strange package..but marked with a coil on the board..then again...220...is probably 220H not uH)

i did find some nice inductors on the HOT side that look to be around 100uH (but i dont wanna use them without measuring or atleast looking up the component datasheet first!)...
also scavenged some nice X class caps aswell as a bunch of diodes and other bits like PTCs

i can get 100uH 3A jobbies at the local for like 5$ a pop...

EDIT: on a side note....im finding it very strange that both the bounce and the current flow issue hasnt been seen earlier (how longs the gbs been around and used on CPCs?!)

WacKEDmaN

#40
ok...another silly question coming at ya @Bryce ! :P

...so which one of these would ya use if ya had to?! blindly without knowing its value?.. im thinking the one with the green core looks about the right size for 100uH.....
the 2 on the right side seem to be mains isolation transformers (4 terminals and 2 winding.. maybe i could use one side of them tho?!)

none are marked except for the 2nd from left (marked with 220 on the top)

inductors and caps really smash me for a 6!.. always have...i fully get how they work and what they do.. but can never put it into practice!

Bryce

The two on the right are common mode chokes, not inductors. The two on the left look like very low current inductors. The third (blue?) one looks like a variable inductor from an audio filter. Only the yellow one looks suitable from a current perspective, but it's most likely a lot less than 100uH.

The exact inductor value really depends on the switching frequency of the SMPSU (or buck). Try the yellow one. The capacitors should be doing most of the work anyway.

Bryce.

WacKEDmaN

#42
thanks for the confirmation mate...

isnt what we're after, "common mode" filtering? (but i guess them common mode chokes are meant for AC and we're playing in the DC domain)

yeah i was thinking the right 2 are probably too low current...
the blue one is actually out of a power supply! (TV)..i dont think its tunable, just wrapped around a ferrite core....i have seen ones with a tunable slug tho

i was thinking the exact value of the inductor shouldnt really matter (aslong as it can handle the current)...it'll just smooth any spikes.. where the 2x caps are doing the actual filtering across the power...

and yes... i AM colourblind! ...i gave up reading resistor values along time ago.. now i just measure em with the multimeter!

Bryce

Common mode is only for AC and mainly removes noise that got picked up by transmission cables (the house cabling).

Bryce.

WacKEDmaN

Quote from: Bryce on 12:42, 03 January 23Common mode is only for AC and mainly removes noise that got picked up by transmission cables (the house cabling).

Bryce.
thank you Sir!.. as i thought....

on another side note....ive got a bunch of linear regulators here...(LM317T in TO-220).. would a linear supply do away with all these issues?
sure the linear is gonna still need filtering on the input side..coz id still be powering the linear via the PC PSU or wall wart... but output should be solid DC.. no switch mode BS!
1.5Amp rating on the linear "should" be alright too yes? (ill whack a chunky heat sink on it!)...i mean ive never seen the CPC go above 1.1A...even with expansions
ive even got the right value resistors to set the adjustable linear to 5.03v (33k and 100k!)

Bryce

Yeah, linear would be a better solution. The heat produced by the LM317T is dependent on the difference between the input and output voltage, so try to keep the input voltage around 3V higher than the desired output voltage. Below 3V it may stop regulating properly and anything above will lower the efficiency and cause the chip to heat up.

Bryce.

WacKEDmaN

Quote from: Bryce on 13:41, 03 January 23Yeah, linear would be a better solution. The heat produced by the LM317T is dependent on the difference between the input and output voltage, so try to keep the input voltage around 3V higher than the desired output voltage. Below 3V it may stop regulating properly and anything above will lower the efficiency and cause the chip to heat up.
Bryce.
awesome!... ill get to building something up tomorrow....input filtering and linear reg on a single board..
thanks again Bryce

heres my back of an envelope hand drawn circuit!...yours is far from shitty Bryce! 




CaptainRon

WacKEDmaN I already sent you these in your messages but thought it might help someone else if they have this issue in the future. 

I tried to replicate the issue using a 5v 2.5a cheap wall wart power supply connected to both the GBS8200 and the CPC through a splitter. I also tested the current draw of the GBS with the CPC powered off but still in circuit on the RGB connector and the DC power jack. I connected a bench supply through a multimeter and used the ground and +5v solder joints on the CPC barrel connector to inject the voltage while checking the current draw of the GBS. 

I could not reproduce the bounce, and the GBS does seem to draw around 300 milliamp. 

Video trying to reproduce the bounce
https://drive.google.com/file/d/1dtFQr8thFjTCv8nIHGRFaAL2i4sBzmm9/view?usp=sharing

Video of the ammeter test of GBS from the CPC barrel jack while CPC is powered off
https://drive.google.com/file/d/1e7R8Cpk1ZKHlRad3ifgSWQb3S-WXhs1h/view?usp=sharing 

Pic of my GBS8200 board
https://drive.google.com/file/d/1eNlulzDnA-aafDRmm5SH5CopeUr6KrzX/view?usp=sharing
If anything's gonna happen, it's gonna happen out there.

WacKEDmaN

#48
thanks mate.... strange ya not seeing the bounce... i wonder if its something with 60hz vs 50hz mains....

i found my bucks run at 52hz.....

but im still finding it really strange there is power flowing through the CPC and GA when its off... ...and that the current going into the CPC INCREASES if ya pull the video connector from the back while its powered on...

gonna grab some new inductors n caps for the filter tomorrow....

@Bryce .. im i right in thinking that the GBS should be SINKING current through the vga connectors....not SOURCING?
im beginning to think about putting diodes on the RGB+S+GND lines so power cant get back into the CPC with it off...

SerErris

Diodes will have a forward voltage drop and a forward voltage minimum. The lowest I know of has 0.4 volt drop (and minimum voltage to actually even work). 

So you will drop at least 0.4 volts of your max 1V RGB voltage.

More typical diodes will drop 0.7 volts and will make your picture all black, as this is the video standard threshold between all black and all white. (0.3 means black, 1v means white).

So no, diodes in the RGB path will not help anything.
Proud owner of 2 Schneider CPC 464, 1 Schneider CPC 6128, GT65 and lots of books
Still learning all the details on how things work.

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