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Author Topic: Schneider 7200 revived  (Read 1433 times)
gertk
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gertk64
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« on: March 11, 2012, 03:37:46 PM »

Another piece of history restored:

A defunct Schneider 7200.

After powerup it just displayed a dull grey screen and no sound or any activity whatsoever. Doing some standard checks (powersupply etc.) giving no strange values it was time to bring up the oscilloscope.

The CPU was running OK but the videochip 8245 was totally 'silent'. It turned out to be the 74LS04 inside the metal box which was happily oscillating but the final buffer port towards the 8245 had input but no output. After replacing this chip (only had an old 7404 lying around, the rest were all 'modern' 74HC04 which would not work without modifying the circuit) the 7200 came back alive.
The most work was removing the metal box without damaging the circuitboard. The defective 74LS04 was simply cut out leg-by-leg first. Then the remaining pins were removed. The holes sucked empty with a vacuumpump and a nice quality DIL socket inserted in place.

The powerswitch was also bad but after some minor plastic reworking the switches I used in the 7400 will also fit inside the 7200.

The Schneider was very dirty inside and out but after some cleaning up it is a lot better, not in mint condition alas: there is a small piece broken off from the blue top casing, front edge left bottom side.

Endresult:
« Last Edit: August 19, 2012, 07:59:00 PM by gertk » Logged

>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
gertk
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« Reply #1 on: March 11, 2012, 03:38:39 PM »

This is the replaced chip. (pos. 660)
« Last Edit: August 19, 2012, 07:59:34 PM by gertk » Logged

>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<
Seob
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« Reply #2 on: March 12, 2012, 07:36:14 PM »

great work
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