Dragon 32: Part 2

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The Clueless Engineer

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Published on February 14, 2023 4:59:05 PM ● Video Link: https://www.youtube.com/watch?v=1_USfg3G3Tw

Duration: 31:22

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I don't get around to using the CoCoSDC in this part. I do, however, check out the 2nd Dragon 32 I have.

01:27 ... keyboard is cleaned
02:35 ... close-up of main board components
03:52 ... FORESHADOWING ...
04:22 ... almost re-assembled
04:37 ... top-case cleaned, new label
05:50 ... comparison with TS1500
06:46 ... 2nd Dragon 32
08:37 ... quick comparison
11:15 ... magic smoke
12:30 ... finally do the TS1500 comparison
13:40 ... dodgy components removed
15:00 ... new components
17:11 ... close-up of 2nd Dragon 32 main board
18:15 ... difference noticed between the two Dragons
20:30 ... testing 2nd power supply
21:30 ... power-on test of 2nd Dragon 32
23:15 ... checking the VDG bodge resistor
24:54 ... side-by-side comparison of video output
26:20 ... close-up of VDG bodge in 1st machine

The 1st machine is all cleaned up.

I test the 2nd machine and immediately blow a tantalum (C11, 4.7µF right next to power input). Once replaced the machine behaves itself.

The 2nd machine has the same Issue 5 Mk II main board but has an Issue 6 power supply board (compared with Issue 4 for the 1st machine). The main difference is the UHF modulator - the Issue 4 modulator has four input wires vs. two in the Issue 6 modulator.

The video output is a little different - a bluer border in the 2nd machine compared with a greener border in the 1st machine.

I noticed that the 1st machine has a pair of bodge resistors on the VDG (MC6487). In particular it has a 15kΩ resistor from pin 10 (ØB or B-Y signal) to pin 4 of IC10 (V- inverting input of a CA3100E op. amp.). {Update: this is apparently the "Sony mod"}

Part 1:
https://youtu.be/72LvEHGdzIQ

Part 3:
https://youtu.be/o0xAoE05nHc


Dragon Data
Tandy TRS-80 Colour Computer
CoCo