Bad Video on STFM

[Dreamstate]

Hi, all.  I have a 520 STFM and I am having a strange issue.  If I use RF, I can see everything but everything is very grainy like static.  If I use SCART RGB, I can see that there is a picture, but I can’t get it to sync to anything.  It is distorted and rolls or is too out of sync to stay.  I am getting a loud feedback sound over the SCART audio as well.  I just recapped the PSU, but no change.  The system works, is booting fine and when I can see enough, the mouse can click and move around.

 

Does this sound like a Shifter or Glue issue or would those cause errors?  Any advice on troubleshooting would be appreciated.

[ParanoidLittleMan]

It can be something in color encoder circuit too - MC1377 and around , located in RD modulator case by STFMs . Composite sync is generated there, and Scart uses it.

Surely is worth to try with replacing Shifter, Glue .  Also check is 12V power line well filtered, voltage ..

[Dreamstate]

Thanks for the info.  I did check the power and it is Ok.  I'll pull out the schematics and poke around that color Encoder.  That sounds like the best place to start.  Finding a replacement Shifter and Glue seems a bit harder at the moment and I hate to buy them if they are not the issue.  I'll keep it on the table, though.

[atarian1]

Are you using a monitor that can sync down the 15kHz horizontal scan rate that the ST needs to display a picture?  Especially when you are using RGB SCART.

 

Actually, the RF output sounds right. It's really not that great of an output signal.

 

Pictures could help.

[ParanoidLittleMan]

If there is Scart connector on TV/monitor it should support 15 KHz scan rate - because it was made for such devices - VCRs, old computers with PAL, NTSC video outputs .

[TGB1718]

2 hours ago, atarian1 said:

Actually, the RF output sounds right. It's really not that great of an output signal.

Not really, it's not the greatest, but very usable, shouldn't be "like grainy/static"

On 7/18/2022 at 4:00 AM, Dreamstate said:

I am getting a loud feedback sound over the SCART audio as well.

Are you sure the monitor is ok, can you try it with something else, also is the cable properly shielded.

The 0V connection needs to be attached both ends and to the shield.

[Dreamstate]

5 hours ago, ParanoidLittleMan said:

If there is Scart connector on TV/monitor it should support 15 KHz scan rate - because it was made for such devices - VCRs, old computers with PAL, NTSC video outputs .

I am running it through a Retrotink 5X and it can handle the 15 KHz.  I can see looking at the statistics that that is what is coming through to the TV.  Since it is being upscaled, I know the TV can handle it fine.  It was working Ok, but a bit shaky but just kind of stopped.  RF always looked poor and I am running it though my VCR to get a composite out.  I did some small tests yesterday on the MC1377 chip and I know it is at least getting the correct voltage at the chip itself. 

 

Based on the multiple responses, I'll switch TV/Monitor tonight just to make sure it is not the issue.  I don't have another SCART option right now except the Retrotink so I can't remove it, but it should not have any issue with the 15 KHz.  I don't think it can handle the Mono High mode, but I am not really trying that at this point.

3 hours ago, TGB1718 said:

Not really, it's not the greatest, but very usable, shouldn't be "like grainy/static"

Are you sure the monitor is ok, can you try it with something else, also is the cable properly shielded.

The 0V connection needs to be attached both ends and to the shield.

I do have another cable on order to make sure it can get ruled out and I have a 1040STe that I bought that should arrive today.  Having that should help me start troubleshooting better since I can see what it does on that system.  At the moment, I have too many single points that I can't rule out.

 

5 hours ago, atarian1 said:

Are you using a monitor that can sync down the 15kHz horizontal scan rate that the ST needs to display a picture?  Especially when you are using RGB SCART.

 

Actually, the RF output sounds right. It's really not that great of an output signal.

 

Pictures could help.

If I can't get to the bottom of it shortly, I'll capture some video and post it for you guys.  Having a second ST in the house will hopefully give me a much better picture.

 

Thanks to everyone.

[Dreamstate]

Well, in the end, the SCART cable had a pin mis-wired.  Moved it the correct pin and it worked!  I’ll let the guys that sell it know to be more careful in the future. Thanks for the help!

[ParanoidLittleMan]

Interesting .. I guess that it was composite video line - since it carries sync signals too, actually in RGB mode sync signals are only used by TV from it.