WASHINGTON (AP) — Federal regulators have fined 13 brokerage firms, including Charles Schwab, JPMorgan Securities and TD Ameritrade, accusing them of failing to protect retail investors in sales of high-risk bonds issued by Puerto Rico's debt-strapped government. Retail investors usually buy securities in smaller amounts, so the rule is designed to ensure that high-risk "junk" bonds are sold only to investors who can purchase bigger quantities and shoulder greater risk.