mnielsenau Posted April 8, 2021 Share Posted April 8, 2021 Hey Guys, Have just installed an F18A in a beige (non v2.2) console and whilst the image on screen is crystal clear, I am getting some herringbone waves (ground loop interference) on the screen. I am using a VGA to HDMI (USB powered) adapter as I do not have a monitor at the moment that has a VGA connector. I have tried the usual ground loop correction things like having the monitor and the TI plugged into the same wall socket etc. I have also tried a number of different brands and model numbers for VGA to HDMI converters. Some are better than others, but all have some sort of interference that comes in waves from time to time. I am considering ferrite beads on all of the wires, but I just need to get some to test. I am running V1.8 of the firmware as when I tried V1.9 there was some strange blurring effects on some spots on the screen. Also the herringbone waves were still there so I downgraded back to V1.8 which at least is clear apart from the waves of interference. I also made sure that there was no interference on screen with the original 9918A chip installed before I installed the F18A. I was wondering if anyone else had seen this issue and if anyone has any advise as to how to rectify? I absolutely love the F18A and I can't wait to see its screen without the interference. Thanks for your help. Cheers, mnielsenau Quote Link to comment Share on other sites More sharing options...
RickyDean Posted April 8, 2021 Share Posted April 8, 2021 Have you tried the f18a on just a vga monitor? If the screen looks crisp and clear then I would say it is a converter issue. I recently got my f18a and it looks good on its intended target a vga monitor, I will have to see how it performs on one of my HDMI converters. Quote Link to comment Share on other sites More sharing options...
+arcadeshopper Posted April 8, 2021 Share Posted April 8, 2021 yes occam's razor is the converter is the likely culprit.. try a retrotink OR a real vga monitor.. they can be found at goodwill usually for cheap 1 Quote Link to comment Share on other sites More sharing options...
wierd_w Posted April 8, 2021 Share Posted April 8, 2021 If they werent such boat anchors, that cost more to ship than they are worth... I would give one of the . (ahem) small collection in my upstairs storage. Quote Link to comment Share on other sites More sharing options...
mnielsenau Posted April 9, 2021 Author Share Posted April 9, 2021 (edited) Yep I definitely think it is the VGA to HDMI converter, but I think I will try the ferrite beads on a few of the cables before I invest in a Retrotink. Else I will go and buy a refurbed $30 4:3 VGA LCD monitor on Facebook marketplace.... Am loving the F18A - I don't know how I managed to get along without using 80 columns for all those years... @arcadeshopper Thanks for the tip on using Force Command on TIPI... Love that command line interface - am reliving my MS-DOS days all over again! Edited April 9, 2021 by mnielsenau 1 Quote Link to comment Share on other sites More sharing options...
mnielsenau Posted April 9, 2021 Author Share Posted April 9, 2021 13 hours ago, wierd_w said: If they werent such boat anchors, that cost more to ship than they are worth... I would give one of the . (ahem) small collection in my upstairs storage. @wierd_w Thanks for the offer on the VGA monitor but you are right the shipping to Singapore would be HORRENDOUS Quote Link to comment Share on other sites More sharing options...
globeron Posted October 9, 2021 Share Posted October 9, 2021 Suddenly my Beige TI locksup to the F18A screen and sound has been working for long time. Any clue what it can be? Switched now to my spare one with F18A. Quote Link to comment Share on other sites More sharing options...
globeron Posted October 9, 2021 Share Posted October 9, 2021 1 Quote Link to comment Share on other sites More sharing options...
+9640News Posted October 9, 2021 Share Posted October 9, 2021 I got that screen when the F18 was loose in the socket. 1 Quote Link to comment Share on other sites More sharing options...
globeron Posted October 9, 2021 Share Posted October 9, 2021 26 minutes ago, 9640News said: I got that screen when the F18 was loose in the socket. Okay will try to open up and reseat it hope that works. 1 Quote Link to comment Share on other sites More sharing options...
GDMike Posted October 9, 2021 Share Posted October 9, 2021 (edited) I've also got one like that and no matter what I do it's just froze in that screen with the screeching noise. I tried placing 4 different 9818s in it, but just got a black screen and one chip made the screen flicker black. But I don't know if these 9818s are any good. But I did think at least one would work. But naa so I pulled the 9818A out and put it in another board, and it's just fine. Edited October 9, 2021 by GDMike Quote Link to comment Share on other sites More sharing options...
matthew180 Posted October 9, 2021 Share Posted October 9, 2021 @globeron When that happens, something else is going wrong with your 99/4A. *Unlike* the 9918A, the F18A powers up with the display enabled and VRAM initialized with useful data, i.e. characters and such so you get some sort of indication that it is working. You usually don't see this "F18A screen" because the host computer usually initializes the VDP very soon (in CPU time frames) after power on. The fact that the 99/4A is not talking to the F18A, yet it did previously, would indicate something has started to fail in your console. If it is a power supply problem, be aware you can blow your F18A up if it gets more than 5.5V on the power pin. 5 hours ago, GDMike said: I've also got one like that and no matter what I do it's just froze in that screen with the screeching noise. The "screaming banshee" is well documented. The default power-up mode for the sound chip (sn76489) in the 99/4A is such that is it making a tone, so one of the first things a computer using the sn76489 sound chip needs to do is turn the sound chip *off*. That is actually how the 99/4A emits a tone when you power it on, i.e. it is the fact that the sound chip has not been turned "off" yet. If your 99/4A is screaming, then the CPU has not executed enough of the power-on code to turn the sound chip off. This could be a lot of things, but the VDP is usually not one of them. The sound chip gets its clock from the VDP (9918A, or F18A in this case), so the fact that you hear the tone means the sound chip is getting its clock and has powered up correctly. Since the 9918A powers up "blind" (as mentioned above, with the display disabled since all the VDP Registers are zero until programmed by the host computer), a console with a 9918A will not display any video if the CPU is not executing its startup code, and the 9918A remains uninitialized. With the F18A, if you see the "F18A screen", then you at least know the 5V is good, the F18A is working, and the sound chip is getting its clock (which comes from the F18A). Since the other 9918A chips you tried also resulted in the screaming banshee, I would say there were probably all fine. Your problem is something else, i.e. bad ROM (doubtful), CPU failed, bad buffer IC on the address or data bus, bad +12V or -5V (the CPU needs 3 voltages), etc. 2 Quote Link to comment Share on other sites More sharing options...
GDMike Posted October 10, 2021 Share Posted October 10, 2021 (edited) Exchanged PS, same issue. It turned out ok, but a bad motherboard doesn't hurt my feelings, as I always want an extra keyboard, PS, extra parts. Since I have 4 consoles..it's just ok to figure 1 mb might go bad. My other three are beautiful. And two have F18A. But I wasn't going to pull another F18 out to test, since that whole computer works. I'll just use the good parts and put aside the Bad MB for now, sounds like the sound Chip is good too. I'm ok with that Edited October 10, 2021 by GDMike 1 Quote Link to comment Share on other sites More sharing options...
globeron Posted November 1, 2021 Share Posted November 1, 2021 Today had some time and swapped the motherboard all is fine now with F18A. But the broken one gives a black screen with a 99xx chip in it (i need more time because i think i plugged the wrong one. A PAL into a NTSC one.) but also i saw this suddenly on the top it is broken, can these break spontaneously? (I am not an electronic expert, i guess it is a resistor that need to be replaced?) 1 Quote Link to comment Share on other sites More sharing options...
Hans23 Posted November 1, 2021 Share Posted November 1, 2021 The broken resistor (R402 6.8k) is part of the cassette interface and won't be causing issues with your video output. You'll have to replace it if you plan to save to cassette. 1 Quote Link to comment Share on other sites More sharing options...
GDMike Posted November 1, 2021 Share Posted November 1, 2021 Slap a resistor there, you have plenty of work area for another. Quote Link to comment Share on other sites More sharing options...
Tursi Posted November 1, 2021 Share Posted November 1, 2021 I've never seen one break spontaneously... that suggests an impact. it looks like the nearby white strip may also be damaged - I don't know much about those but I know damaging them can prevent a boot. Quote Link to comment Share on other sites More sharing options...
matthew180 Posted November 1, 2021 Share Posted November 1, 2021 Resistors spontaneously break? No. They can blow up, though, if things are going really bad. But in that case you would see a lot of burned components and such. If the white strip, that Tursi pointed out, is actually damaged, then that can prevent your system from working. Those strips carry power distribution (+5, -5, +12, ground) to various parts of the system. I always thought they were just for noise, but found out the hard way (by pushing one too far out of the way and breaking it), that they are critical to the PCB working. Whole sections of the motherboard remain isolated if you break the wrong ones. They are hard to solder too, since they are basically big pieces of copper wrapped in insulation. Be nice to the white strips. 1 Quote Link to comment Share on other sites More sharing options...
+dhe Posted November 1, 2021 Share Posted November 1, 2021 I think Karl Guttag called them 'bus bars'. Quote Link to comment Share on other sites More sharing options...
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