CMVS - RGB brightness levels

MtothaJ · Sep 7, 2015

On a MV-1FZ board I have 75ohm resistors on the RGB lines and its giving me perfect brightness levels when connected via Scart to a Sony Trinitron consumer CRT TV.
However when connecting to a BVM the picture is way too bright. I tried the obvious of getting a separate scart cable and adding some additional resistors - tried 480ohms (so in total 555ohms) - still too bright and washed out. Any ideas WTF is up and how to rectify?

Xian Xi · Sep 7, 2015

Check the video levels on the BVM, the brightness/picture level could be turned way up.

donluca · Sep 7, 2015

I have your exact same setup ( BVM 14M4DE + MV1FZ ) and the picture is just a little bit too bright with 75Ω resistors so I may try 100Ω out.

Did you put your resistors to ground or in-line? You want a voltage divider so, since the BVM should auto-terminate connections with 75Ω (to the ground), you just need resistors in-line to get the levels down.

Get your multimeter and measure the RGB signals. Theoretically, you should get no more than 2V on each one. Then use this http://www.raltron.com/cust/tools/voltage_divider.asp to calculate how big your in-line resistor needs to be. R2 is 75Ω. R1 is the one you put in.

skate323k137 · Sep 7, 2015

Generally with MVS (and many other JAMMA boards) with a PVM I use 220 ohm resistors on R G B and Sync. Never had a board not work well with that.

Also, what XX said... check your brightness / contrast and if there's a service menu check the sub bright too.

MtothaJ · Sep 8, 2015

Thanks for your replies. The 75ohm resistors are in line, I think that it is a question of dialling down the brightness levels of the BVM. Most other consoles I have seem to display fine although that's with the brightness dial turned almost all the way down. Just to check whether I should look at the service menu or whether there are some pots in the BVM where I would turn it down.

SmokeMonster · Sep 8, 2015

Instead of resistors, 1K pots may work better in your setup.

On my jamma harness I have 1k pots followed by 220uF caps on RGB. I did this to make switching between CPS2 and MVS easier. Is this a good way to wire it?

MtothaJ · Sep 8, 2015

SmokeMonster said:
Instead of resistors, 1K pots may work better in your setup.

I have 1k pots on my supergun followed by 220uF caps on RGB. I did this to make switching between CPS2 and MVS easier. Is this a good way to wire it?

I was thinking about 1k pots also - my supergun has a triple pot for the RGB lines which I haven't adjusted since I got it and from what I checked it is set at 550ohm - this was the reason why I tried to mod the scart cable to get to c.a. these values.

gtdoering · Sep 21, 2015

I've had good results with either 120ohm resistors in line and 1k pots as well. It takes some experimentation to find which setup works best for your TV. I use 1k pots on my CMVS with my 20 inch PVM.

Pasky · Sep 22, 2015

Did you terminate the passthrough on the BVM? That may be the issue.

http://www.ebay.com/itm/10-PCS-BNC-Male-Terminator-75-Ohm-/330891117782?hash=item4d0aa5c4d6

If it works fine on the Trinitron, I'd bet money that your signal isn't being terminated at the BVM and is therefore twice the strength (1.4vpp instead of 0.7vpp)

MtothaJ · Sep 24, 2015

Pasky said:
Did you terminate the passthrough on the BVM? That may be the issue.

http://www.ebay.com/itm/10-PCS-BNC-Male-Terminator-75-Ohm-/330891117782?hash=item4d0aa5c4d6

If it works fine on the Trinitron, I'd bet money that your signal isn't being terminated at the BVM and is therefore twice the strength (1.4vpp instead of 0.7vpp)

Thanks for this suggestion, I was pretty sure the BVM auto terminated @75ohm but it cant hurt to give this a try. Have already ordered the terminator caps, will report back once i recieve these.

MtothaJ · Sep 25, 2015

PASKY IS THE MAN!

Got the terminator caps today and all I can say is...

PASKY IS THE MAN :mr_t:

This has made all the difference - not only for the Neo but also for other consoles on the BVM. Previously it was still an excellent image but overly bright, even with brightness turned all the way down. Its interesting how much of a difference that 75ohm terminator makes on the BVM end. As mentioned in the thread I was pilling on the ohms at the scart plug cable end but to no avail - now I just use a standard scart cable. Maybe its something I missed but considering how crucial these terminator caps are not a whole lot has been written on the subject when discussing connecting a PVM / BVM.
In any case, thanks again, really happy with the results :glee:

city41 · Oct 4, 2015

What do the terminator caps do? Do you put them on the rgbs outputs used for daisy chaining? Why do they help?

MtothaJ · Oct 5, 2015

city41 said:
What do the terminator caps do? Do you put them on the rgbs outputs used for daisy chaining? Why do they help?

Basically they tell the monitor that no other monitor is daisy chained in - without them the signal is twice as strong as it should be to accommodate two displays, leading to e.g. excessive brightness. They are to be placed on the RGBS BNC output connectors on the monitor, just as you mentioned. RGB TV's and smaller PVM / BVM's without the daisy chaining connectors have these terminators built it, and that is why I was initially getting a great picture on the consumer Trinitron but a too bright image on the BVM. Also just to clarify the obvious in terms of wording - we are talking about terminator caps, but for the avoidance of any doubts they are not capacitors but resistors to match the output impedance as per RGB specs.

Heinz · Oct 5, 2015

MtothaJ said:
Basically they tell the monitor that no other monitor is daisy chained in - without them the signal is twice as strong as it should be to accommodate two displays, leading to e.g. excessive brightness. They are to be placed on the RGBS BNC output connectors on the monitor, just as you mentioned. RGB TV's and smaller PVM / BVM's without the daisy chaining connectors have these terminators built it, and that is why I was initially getting a great picture on the consumer Trinitron but a too bright image on the BVM. Also just to clarify the obvious in terms of wording - we are talking about terminator caps, but for the avoidance of any doubts they are not capacitors but resistors to match the output impedance as per RGB specs.

I'm wondering here, I've got a PVM 20M4A with RGBS outputs as well as inputs. I don't seem to have any terminator caps but is it necessary for every monitor with those outputs?

donluca · Oct 5, 2015

MtothaJ said:
Basically they tell the monitor that no other monitor is daisy chained in

Actually quite the contrary: they fake another monitor daisy chained to the current monitor if it doesn't auto-terminate by itself.
This is quite strange as AFAIK all BVMs and most PVMs auto-terminate the connections.

lachlan said:
I'm wondering here, I've got a PVM 20M4A with RGBS outputs as well as inputs. I don't seem to have any terminator caps but is it necessary for every monitor with those outputs?

As I said before, they are not needed normally. I don't understand why some pro Sony monitors don't auto-terminate, go figure.

CMVS - RGB brightness levels

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