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I'm trying to get an old C128 working again. Lacking a C128 power supply, I've attached a C64's power supply's 9VAC and am supplying 5VDC from a bench power supply (with a 2A limit at the moment).

There's an old CRT TV attached to the Composite output and an old Commodore 1404 screen (which might or might not be working) is attached to the DB9 socket.

Switching the C128 on immediately draws 2A. Neither screen shows any kind of output. As far as I can tell with a quick check, the only IC that gets warm (but not hot) is the 7812. There are no funny noises or smells.

My question at this point is mainly whether it might make sense to try with a 3 amps limit?

(In case anyone happens to be hanging around 35C3, I'm at doubleoctothorpbuero (just type "double" in the C3Nav and it'll autocomplete). Thankful for any hints or pointers! :-))

Edit: thank you for the comments. I've added a question that should make it clear what I'm asking. But please keep it on hold for now as I'm trying to follow @'Brian H''s suggestion of finding a known-good device to test monitor and power supply with. Given that there's a PDP11 standing down the hall, there should also be plenty of at least C64 around here.

closed as unclear what you're asking by wizzwizz4 Dec 28 '18 at 16:03

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  • I'm not certain what your question here is. Please read the tour, then edit your question to be clearer. – wizzwizz4 Dec 28 '18 at 16:03
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    The question is quite obvious, it's in the subject. – Maury Markowitz Dec 28 '18 at 16:31
  • This hardwarebook.info/C128_Power_Supply says 5V at 2.5A. If you are limiting to 2A and are at that limit, the voltage will be less than 5V so nothing is likely to work. Try increasing the limit to 3A. If you are still current limited, you need to find out why before you do anything else. – alephzero Dec 28 '18 at 16:32
  • A known-working C64 or C128 would come in very handy here, as you are working with several independent variables. I'd want to confirm my Power Supply rig and video displays were good-to-go before going any farther. – Brian H Dec 28 '18 at 16:50
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    @alephzero: Didn't find a known-working C64 yet. Did try with 3A, and the voltage still drops to around 3.75V. Really, really curious. – Rainer Verteidiger Dec 28 '18 at 18:09