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wagiminator / C64-Collection

Collection of cartridges, adapters, and replacements for the Commodore C64
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USB-C to 1541-II Power Adapter Low Voltage #10

Open TankedThomas opened 1 year ago

TankedThomas commented 1 year ago

Hi Stefan, sorry to bother you again.

I got the power adapters made by JLCPCB (5 PCBs minimum, of course) and had them assembled because I can't do SMD work myself.

For the most part, they work fine - the voltages are within about 5% tolerances (most are much closer). None hit 12V on the dot but it's close enough (about 11.9V). Some hit 5V and some are just under (about 4.9V), so that's fine. However, when hooked one up to my 1541-II, the drive is only drawing an absolute maximum of 4.37V on the 5V rail. The 12V rail seems fine though.

I should add that I don't know if the 1541-II fully works as it was in bad condition and I've been refurbishing it (nor does it have the original PSU). I've tested all but the 2003 chip (need to get a replacement soon) and, of course, the SMD amp. All the tested chips were fine except the 251828-03 gate array (tested them in my working 1541C, and tried its 251828-01 gate array chip in the 1541-II to no avail). It seems the amp has some voltage control built into it too but I don't think this is the problem because the 5V rail seems to test the same through it.

So I'm wondering if this is a problem with the power adapter not outputting enough under load, or if there's something I've missed on the drive itself that could be causing the low voltage. The drive's spindle spins but both lights stay on. Best I can tell, it's not getting high enough voltage to reset the drive at boot, but I could be wrong.

I've tried a bunch of USB adapters, at least two of which definitely have the correct specs for powering this adapter. I've spent days troubleshooting this drive, so I thought I'd reach out to you in regards to this power adapter to see if I can rule it out as a problem (or fix it if it is the problem).

wagiminator commented 1 year ago

Hi, first please try to find out if the problem is with the adapter or the drive. There are two ways to do this:

  1. Clamp an ammeter into the 5v line between the adapter and the drive. Turn on the drive and measure the current.
  2. If you have an electronic load, connect it to the adapter's 5V and GND, turn on the load and measure the voltage at a current of 1A.

If the floppy drive is working properly, it should never draw more than 1A of current on the 5V rail. If the adapter is working properly, the voltage should not drop below 4.8V at a 1A load. The voltage drop of the adapter should behave similarly as shown in the following project: https://github.com/wagiminator/Power-Boards/tree/master/78xx_Replacement_SD8942

Also make sure that the individual cores of the connection cable between the adapter and the drive are thick enough (at least 20AWG) to have the lowest possible resistance!