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Looking for insight on the Sol-20

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    Looking for insight on the Sol-20

    I just became the steward of two Sol-20 machines of unknown operability. I am carefully and slowly assessing their status, but I have quickly realized that I have to let go of a lot of the assumptions I've developed over the years about "retro computers." I am coming mostly from the Apple II world, and everything that came after in the 80s. For example, I think I may have taken things like RF Modulation for granted.

    I have a thread going on the comp.os.cpm google group, and there's been some interesting debate about 50 ohm vs 75 ohm coax.

    I wanted to see if a wider audience might be able to help me get to the crux of the issue.

    What is the simplest way to connect the Sol to a TV? Everything I know about that era of computing would tell me to rely on a serial connection or RF modulation for display, and so I think my options are to connect the Sol to an older TV via an RF modulator, or connect it to the composite video of a new TV.

    Also, I can count on one hand the number of fuses I've had to buy in the last 20 years. The user manual only states that a 3A or 3.2A (contradictory statements on different pages) slow blow fuse is required. A quick search turns up 3A fuses, but of varying sizes. Which is the correct size? And finally, at least one of the fuse holders should probably be replaced. I think I have found a replacement part with Littelfuse p/n 03420038, but it looks like there are three variations - 38H, 38X, and 3HXL. Any idea what the suffixes mean and if any of these are compatible?


    Actually for something like computer text and much more so computer graphics, the RF modulator is a very poor option and the video resolution becomes substantially degraded for detail, when the video modulates an RF carrier and that carrier is processed by the tuner and video IF in a TV to get it back to the same video signal you started with.

    You can think of the TV therefore as being a Tuner & IF system to recover the video signal then feeding a video display unit or video monitor.

    Many TV's had 75 Ohm video inputs, for VCR's and this sort of thing. Its better to use those inputs.

    For a SOL-20, there are plenty of good monochrome video monitors about, 9" is a good size, with 75R video inputs , these sorts of things were used in the security industry etc, get something like that for your SOL, rather than a TV set.

    Of course you can hack into the video input section of a TV, ideally you require the set's schematic and sometimes a buffer stage is needed or a stage to invert the polarity of the signal. These are easy to design for those familiar with the requirements of composite video signal and impedance matching and the requirements of wide signal bandwidth.

    If you have a video output stage in a computer, that has been designed with a 50R output impedance, and you terminate it at the TV end with 75R rather than 50R (and even if it is 75 and not 50R cable) there is no significant issue except for a slightly high signal level due to the under-termination, it takes many meters of cable before issues like signal reflections at impedance bumps are problematic for a monochrome video signal. Many video monitors have a high Z switch, lifting the cable termination to a few thousand ohms, and even that gross mismatch doesn't normally cause too much visible trouble, and if the was some loss of high frequency resolution or subtle ringing effects, it would only be a fraction of the loss you see with the RF modulator and TV arrangement.


      fyi, comp.os.cpm isn't a "google group", it's a Usenet news group.

      Proud owner of 80-0007 - The only one of its kind.


        9" B/W monitors meant for studio or security applications are available on ebay at fairly good prices, occasionally, even unused. Beware that some used examples that had been used for security have burn-in in the time/date/"camera" block areas. Because they generally have metal cases, they survive shipping better. and are small and relatively light. The studio monitors in particular have higher specs than a normal consumer TV. I can get good 80x24 resolution on a quality Sony monitor over NTSC, for example. These are not as plentiful as they once were because the HD conversion is getting further in the past.

        BTW, generally, these have 50/75 BNC inputs.

        I would not recommend adding an input into a TV because of possible hot chassis issues, although in the transistor era, this is not likely to be an issue. A monitor is cheap and better. I blew up a TV and almost myself over this once.



          .TD0 files someone created by TELEDISK (SYDEX)
          206416 Feb 9 1993 sol20-3.td0
          281126 Feb 9 1993 sol20-2.td0
          194166 Feb 9 1993 sol20-1.td0

          .IMD files I created with Dave Dunfield's Imagedisk Utilities TD02IMD
          315091 Apr 20 06:23 SOL20-3.IMD
          402811 Apr 20 06:23 SOL20-2.IMD
          286530 Apr 20 06:21 SOL20-1.IMD

          .RAW files I created with Dave Dunfield's Imagedisk Utilities IMDU
          509184 Apr 20 06:24 SOL20-3.RAW
          509184 Apr 20 06:24 SOL20-2.RAW
          509184 Apr 20 06:24 SOL20-1.RAW

          .TXT files I created with Dave Dunfield's Imagedisk Utilities IMDA & IMDU
          9702 Apr 20 06:59 SOL20-3.TXT
          9798 Apr 20 06:58 SOL20-2.TXT
          10751 Apr 20 06:57 SOL20-1.TXT

          CP/M 2.2 System Disk for Morrow Designs w/ Disk Jockey & Sol20 I/O
          SSDD 256 byte sector, 1-26, 1:1
          8" 77 Tracks Single Sided Double Density

          DIR list in SOL20-1.TXT
          $ cpmls -f comb -D SOL20-1.RAW
          Name Bytes Recs Attr update create
          ------------ ------ ------ ---- ----------------- -----------------
          A$ .ASM 10K 71
          ANS .LIB 2K 3
          ASM .COM 8K 64
          BIOPS1 .BAS 2K 2
          BIOPS2 .BAS 2K 2
          BIOPS3 .BAS 2K 2
          CALIB .ASM 2K 9
          CALIB .BAS 2K 2
          COIL .BAS 2K 3
          COIL1 .BAS 2K 4
          COIL2 .BAS 2K 4
          CREF80 .COM 4K 30
          DDT .COM 6K 38
          DISPLAY .FOR 2K 9
          ED .COM 8K 52
          EPROM .BAS 2K 3
          EPS80 .COM 2K 4
          F80 .COM 26K 201
          FORMT# .COM 2K 11
          FORTH .ASM 2K 1
          JUMP .ASM 2K 4
          L80 .COM 8K 58
          LOAD .COM 2K 14
          M80 .COM 18K 137
          MBASIC .COM 24K 190
          MSGS .LIB 2K 6
          OPTO .ASM 2K 3
          PIP .COM 8K 58
          PLL .BAS 2K 6
          PLOT1 .BAS 2K 2
          POSTEST .ASM 2K 1
          POSTEST1.ASM 2K 10
          POSTEST2.ASM 2K 4
          PROB1 .ASM 16K 113
          PROB1 .BAS 2K 13
          PROBE .BAS 2K 6
          PROG .ASM 2K 15
          PROG .FOR 2K 3
          SCAN .ASM 2K 13
          SHAFT .ASM 2K 7
          SLIDE .ASM 2K 10
          STAT .COM 6K 41
          SUBMIT .COM 2K 10
          SYSGEN .COM 2K 10
          TC1 .BAS 2K 3
          TC2 .BAS 2K 2
          TEMFLTR .BAS 2K 4
          TEMFLTR1.BAS 2K 4
          TEMPCAL .BAS 2K 1
          UTIL .ASM 4K 24
          VISC1 .BAS 2K 2
          VISC2 .BAS 0K 0
          VISC3 .BAS 2K 2
          WS .SUB 2K 2
          WSEPSON .COM 14K 110
          WSMSGS .OVR 26K 195
          WSOVLY1 .OVR 28K 222
          WST .COM 14K 110
          58 Files occupying 304K, 192K Free.

          DIR list in SOL20-2.TXT
          $ cpmls -f comb -D SOL20-2.RAW
          Name Bytes Recs Attr update create
          ------------ ------ ------ ---- ----------------- -----------------
          ASM .COM 8K 64
          CATF .ASM 8K 62
          CATQ .ASM 6K 35
          COPY .COM 8K 60
          DDT .COM 6K 38
          EXAM .ASM 8K 55
          F80 .COM 26K 201
          FORLIB .REL 24K 180
          IRS .COM 20K 158
          L80 .COM 12K 84
          LIB .COM 6K 37
          M80 .COM 20K 157
          M80B .COM 20K 150
          MBASIC .COM 24K 190
          OBASIC .COM 18K 129
          PIP .COM 8K 58
          PRODUCT .D03 4K 25
          RECIPE .D04 4K 24
          RELOC .ASM 10K 78
          SEQIO .LIB 12K 82
          SID .COM 10K 80
          STAT .COM 6K 44
          VBOOT31 .ASM 4K 20
          WS .COM 14K 110
          WSMSGS .OVR 26K 195
          WSOVLY1 .OVR 28K 222
          WST .COM 14K 110
          XIRS .COM 24K 182
          28 Files occupying 376K, 120K Free.

          DIR list in SOL20-3.TXT
          $ cpmls -f comb -D SOL20-3.RAW
          Name Bytes Recs Attr update create
          ------------ ------ ------ ---- ----------------- -----------------
          BASCOM .COM 34K 257
          BASCOM .SUB 2K 3
          BASLIB .REL 26K 195
          BCLOAD . 2K 1
          BRUN .COM 16K 121
          CREF80 .COM 4K 31
          ED .COM 8K 56
          EPROMCHK.ASM 2K 6
          EXM125 .TXT 6K 39
          FORMT# .COM 2K 11
          INSTALL .COM 28K 222
          L80 .COM 12K 84
          LIB80 .COM 6K 37
          LOAD .COM 4K 18
          M80 .COM 20K 157
          OBSLIB .REL 48K 378
          PIP .COM 8K 58
          PROMPTER.ASM 12K 82
          RANTEST .BAS 2K 3
          RANTEST .COM 2K 11
          STAT .COM 6K 44
          SUBMIT .COM 2K 10
          SYSGEN .COM 2K 10
          WSU .COM 14K 112
          XSUB .COM 2K 6
          25 Files occupying 268K, 228K Free.