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qmacpoint
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IBM 770 circuit diagrams

Sun May 19, 2019 6:20 pm

So I'm trying to revive this 770 (when I got it I didn't realized there were blown capacitors) - does anyone know where you can get the circuit diagrams for these old laptops? :)
 
just brew it!
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Re: IBM 770 circuit diagrams

Sun May 19, 2019 6:56 pm

You don't need a circuit or PCB diagram to replace bad caps. Just look up the caps based on their markings and find a similar substitute.
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qmacpoint
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Re: IBM 770 circuit diagrams

Sun May 19, 2019 7:52 pm

just brew it! wrote:
You don't need a circuit or PCB diagram to replace bad caps. Just look up the caps based on their markings and find a similar substitute.

That's true - but before I get neck deep on that, I was wondering if there are damaged traces, or similar problems that may happen. Plus this being a super old machine, a diagram like that would help on maintaining it alive as much as it can.
 
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Re: IBM 770 circuit diagrams

Mon May 20, 2019 6:49 am

qmacpoint wrote:
just brew it! wrote:
You don't need a circuit or PCB diagram to replace bad caps. Just look up the caps based on their markings and find a similar substitute.

That's true - but before I get neck deep on that, I was wondering if there are damaged traces, or similar problems that may happen. Plus this being a super old machine, a diagram like that would help on maintaining it alive as much as it can.

You don't need a circuit diagram to spot damaged traces either, and high-density PCBs typically have 6 (or more) layers, so most of the traces aren't even visible; if there's an internal trace that has been blown by a short or over-current condition you won't even see it unless it got hot enough to burn through the PCB material.

TBH I don't think manufacturers have made circuit diagrams available for PCs since the 1980s. If what you really mean is just a placement diagram for the major components, yeah that may be available out there somewhere; but like capacitor values, that could be figured out by looking up part numbers of individual components.
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ludi
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Re: IBM 770 circuit diagrams

Mon May 20, 2019 11:27 am

qmacpoint wrote:
just brew it! wrote:
You don't need a circuit or PCB diagram to replace bad caps. Just look up the caps based on their markings and find a similar substitute.

That's true - but before I get neck deep on that, I was wondering if there are damaged traces, or similar problems that may happen. Plus this being a super old machine, a diagram like that would help on maintaining it alive as much as it can.

AFAIK laptops, even ones as old as that, only fail in a few ways you can do anything about:

1) Power brick or battery failing -- replace power brick or battery. For a late-1990s unit, the battery most likely uses 1.2V NiCd or NiMH cells and could be refurbished.

2) Electrolytic capacitor dried out, or swollen and leaking -- replace any units you can find, like-in-kind.

3) Through-hole solder joint broken behind a connector (very common when power ports were still PCB mounted) -- reflow the solder if the joint is cracked, repair PCB using TC buswire if it lifted or broke the trace.

4) Flexible cable broken internally -- salvage the part from another unit.

5) Component or subassembly not working -- salvage the part from another unit.

There aren't many options beyond that, even if you can decode some of the components. On equipment that old, there might be a couple through-hole fusible resistors that failed, but in that case the problem is downstream and thus see (5).
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