Sideburn,
The circuit that reads the video RAM creates the dot clock (or just passes it on from the main clock generator). That and the two sync frequencies are really the only timings needed to create the video signal. On a standard 600B, the dot clock is simply the crystal frequency. On the 600D in 48-character mode, it is actually double the crystal frequency. I don't know the details of the video mod on your board. Is there just one crystal? It's frequency should be marked on it. I don't think modulating the signal on an RF carrier would do any good, it would still be the same signal when it was demodulated. But who knows?
Improving signal strength on Superboard II
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Re: Improving signal strength on Superboard II
No current OSI hardware
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
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- Posts: 115
- Joined: Sat Feb 03, 2024 10:59 pm
Re: Improving signal strength on Superboard II
I took some measurements.
The crystal is showing 7.81mhz
HS (u70 pin 13) is showing 15.43 kHz
HV (u70 pin 12) is showing 60.24 Hz
The crystal is showing 7.81mhz
HS (u70 pin 13) is showing 15.43 kHz
HV (u70 pin 12) is showing 60.24 Hz
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Re: Improving signal strength on Superboard II
Only one crystal on my board and it’s just blank can.bxdanny wrote: ↑Tue Mar 26, 2024 6:26 pm Sideburn,
The circuit that reads the video RAM creates the dot clock (or just passes it on from the main clock generator). That and the two sync frequencies are really the only timings needed to create the video signal. On a standard 600B, the dot clock is simply the crystal frequency. On the 600D in 48-character mode, it is actually double the crystal frequency. I don't know the details of the video mod on your board. Is there just one crystal? It's frequency should be marked on it. I don't think modulating the signal on an RF carrier would do any good, it would still be the same signal when it was demodulated. But who knows?
Photos of its current state attached:
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Re: Improving signal strength on Superboard II
Only one crystal on my machine, which is a 600D replica, It uses an LS93, U29, to split the clocks up IIRC.
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Re: Improving signal strength on Superboard II
Sideburn,
It looks to me like there are some numbers stamped on the end of the crystal's can, opposite the leads, but I can't make them out. Are they not actually there?
It looks to me like there are some numbers stamped on the end of the crystal's can, opposite the leads, but I can't make them out. Are they not actually there?
No current OSI hardware
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
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- Posts: 115
- Joined: Sat Feb 03, 2024 10:59 pm
Re: Improving signal strength on Superboard II
My mistake.
Yes it says 7.86342
Yes it says 7.86342
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Re: Improving signal strength on Superboard II
7.86432 = 2 * 3.93216 (MHz), or exactly twice the frequency of the standard C1P/SB II crystal. Try replacing it with a crystal of 8.0 MHz even. (I guess you'd have to order one.) That would bring the horizontal frequency closer to the NTSC spec. And while it would also push the vertical frequency away from spec, the result could be good enough for your LCD monitor to display without problems.
No current OSI hardware
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
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- Posts: 115
- Joined: Sat Feb 03, 2024 10:59 pm
Re: Improving signal strength on Superboard II
Ok I’ll order one. Thanks.
You saw I was reading 7.9 mhz off the crystal right?
This good enough ? https://a.co/d/jjziXi1
You saw I was reading 7.9 mhz off the crystal right?
This good enough ? https://a.co/d/jjziXi1
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Re: Improving signal strength on Superboard II
I guess so, yeah.
No current OSI hardware
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
Former programmer for Dwo Quong Fok Lok Sow and Orion Software Associates
Former owner of C1P MF (original version) and C2-8P DF (502-based)
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- Posts: 115
- Joined: Sat Feb 03, 2024 10:59 pm