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Thread: Original Tandy 1000 no boot

  1. #81
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    Quote Originally Posted by falter View Post
    So I've been looking at the RDDATA line, and I see a fairly clean signal up to U107. The signal looks good and clean going into the hex inverter at pin 13 but coming out it seems weak, like it was with the 7432, and then it looks weak coming into pin 1 of the FDC at U69.

    I'm a little weak on how hex inverters handle this sort of thing. It looks like signal comes from pin 30 (RDATA), to pin 1 of U85 (74LS14), then gets inverted out pin 2, then hits U107 at pin 13, and gets inverted again at 12. So I should be seeing pretty close to the same sort of signal out of pin 12 of U107 as I'm seeing at pin 1 of U85 right?
    I was about to suggest the RDDATA line, but the page wasn't submitting my post for some reason, but I see you're on top of that.
    Can you use the oscilloscope to measure the voltage coming out of the inverter at pin 12? The FDC9216 splits the MFM read signal into the seperate data and clock signals, so a voltage drop could interfere with what the FDC gets from the splitter.
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

  2. #82
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    Looks like a little less than 1V at pin 12?

  3. #83
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    Quote Originally Posted by falter View Post
    Looks like a little less than 1V at pin 12?
    Yeah, that gate is borked. Should be outputting at least 2.7v in the high state, nominally 3.4v.
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

  4. #84
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    Replaced - voltages look ok.. but still no difference.

    I had a look at the FDC9216 chip next out of curiosity. If I'm reading the block diagram right, I should be seeing a clock coming out of pin 2 (SEPCLK), and some data coming out of pin 7 (SEPD). SEPD doesn't seem to have anything coming out (stuck high), and SEPCLK doesn't have any discernible clock signal. REFCLK has a clock signal. Am I understanding the function of this correctly?

  5. #85
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    SEPD* and SEPCLK are both "separated" from the floppy disk drive combined (modulated) data signal (active low). The REFCLK is the clock input from the oscillator circuit, which should be 8MHz divided by 2. Assuming the new '04 chip you installed at U107 is producing an active-low data signal, but the FDC9216 is not giving proper outputs, maybe check to see if the reference clock at pin 3 is actually operating at 4 MHz? It's possible that the FDC9216 is bad too, but I'm kinda wondering what would cause all these chips to go bad in the same section of the board. Almost as if somebody just dragged a 12v wire across the board and it touched several pins along the way.

    Wow. This board is turning out to be quite the problem child, isn't it?
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

  6. #86
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    If you end up having to replace the FDC9216, I'd order a replacement for the uPD765 as well, the way things are going. They're both cheap as borcht on eBay.
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

  7. #87
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    Quote Originally Posted by blackepyon View Post
    SEPD* and SEPCLK are both "separated" from the floppy disk drive combined (modulated) data signal (active low). The REFCLK is the clock input from the oscillator circuit, which should be 8MHz divided by 2. Assuming the new '04 chip you installed at U107 is producing an active-low data signal, but the FDC9216 is not giving proper outputs, maybe check to see if the reference clock at pin 3 is actually operating at 4 MHz? It's possible that the FDC9216 is bad too, but I'm kinda wondering what would cause all these chips to go bad in the same section of the board. Almost as if somebody just dragged a 12v wire across the board and it touched several pins along the way.

    Wow. This board is turning out to be quite the problem child, isn't it?
    Pin 3 seems to be 4mhz.. so.. yeah.

    I'm curious if all original 1000 boards had all these little jumper wires. The 74ls04 I replaced had three connected to it and I see a bunch elsewhere.

  8. #88
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    Quote Originally Posted by falter View Post
    Pin 3 seems to be 4mhz.. so.. yeah.
    Well, if it's getting a good clean input then the FDC9216 is probably bad too, assuming that the socket, if it's using one, is still good (the 1000A has it socketed, so this part might have had a failure rate?). Fortunately, as we've said, they're pretty cheap.

    Quote Originally Posted by falter View Post
    I'm curious if all original 1000 boards had all these little jumper wires. The 74ls04 I replaced had three connected to it and I see a bunch elsewhere.
    These follow the traces in the schematics, I assume? It's not unusual to see bodge wires on PCBs from the 70's and 80's, especially first runs. CAD software was in it's infancy back then, and the traces on these boards would usually have been laid out by ruler, pen, and stencils on a drawing table. Because of the cost of manufacture, you'd bodge-fix the stock of first runs to use them up, and fix the problem before you submit the design for the next run. These days, any circuit design software will run a check to make sure there's no nets left dangling in the wind before you send the design off for manufacture.

    This was also before PTH became common practice, so it was pretty easy to lift traces on these boards.

    While you're waiting on that FDC9216, I'd highly recommend testing end to end on the other lines too, just to make sure there' no other bad ICs.

    If it's not asking too much, would you be able to snap a high-res photo of the motherboard, so that I can see how the ICs are arranged? I can only find one of the 1000A online (which is laid out a bit differently), and I'm trying to figure out what the common cause would have been to bugger up the floppy control circuitry like this, especially if the rest of the system seems to be working.
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

  9. #89
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    Not a problem at all -- I appreciate all the suggestions/help very much.

    Here's the high res shots of the board:

    https://drive.google.com/file/d/1meg...ew?usp=sharing
    https://drive.google.com/file/d/1mdU...ew?usp=sharing

  10. #90
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    Nice! The board's a bit grungy, but I can clearly see the labels. I'll see if I can discern anything from this.

    I see what you mean about the bodge wires. As I said, it was common practice, and the price of PCB manufacture has gone down significantly in the past 40 years.
    My vintage systems: Tandy 1000 HX, Tandy 1000 RSX, Tandy 1100FD, Tandy 64K CoCo 2, Commodore VIC-20, Hyundai Super16TE (XT clone), and some random Pentium in a Hewitt Rand chassis...

    Some people keep a classic car in their garage. Some people keep vintage computers. The latter hobby is cheaper, and is less likely to lead to a fatal accident.

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