I think this is the technology that Paul Krugman has in mind:
1. C + Kdot = A.La.K(1-a)
C is consumption, K is the capital stock, Kdot is investment, L is employment, A is a parameter that represents productivity, a is a parameter that (in competitive profit-maximising equilibrium) will equal labour's share of national income, so (1-a) is capital's share. (I've ignored physical depreciation of capital for simplicity).
Macroeconomists commonly assume this technology, mostly because it's easy to work with. But this technology creates a problem for Paul. That's because with this technology (in competitive profit-maximising equilibrium) the (real) rate of interest equals the rental rate on capital goods (equals the Marginal Product of Kapital), and Paul wants to explain why capital income has gone up while the rate of interest has gone down. (So he has to assume that monopoly power has increased, and that what looks like an increase in capital income is really an increase in monopoly rents.)
Let me make one small change. Change 1 to:
2. C + Kdot/A = La.K(1-a)
(I've divided both sides of 1 by 'A', then deleted the 'A' underneath 'C'.)