[sdiy] Roland's MB187123 / RD87123 Alpha Juno DCO chip

[brianw]

They might literally be TEST pins ... ones that you don't want to use without documentation.

The Ensoniq Performance Sampler has a menu that is barely hidden and can be reached with a few button presses. There are warnings everyone not to enable any of the test modes on that screen because it will damage the sampler. I never learned what sort of tests they put in the firmware that could destroy the hardware, but it's at least one example of something the manufacturer thought was necessary, even though it was not useful to customers.

I suspect that the TST pins are grounded so that they force "normal" operations instead of any sort of test mode. Perhaps it's something used to test the chips before they're soldered into a product.

Brian


On Aug 24, 2026, at 3:37 PM, Tom Wiltshire <tom at electricdruid.net> wrote:
> Finally, I'm sort-of curious about those two "TST" pins. Looks like "Test" to me. but what does a test mode do on such a chip, and why didn't Roland use it in the Alpha Juno? (both lines are tied permanently low). Maybe that's not it.
> 

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