Posted By
Dbrownlee
on 2025-08-01
12:13:57
|  Plus 4 Power issue No LED
New to Plus 4. I bought a modern C64 power supply and a C64 to Plus 4 square socket adapter. I have good voltage readings at the connector 5.06DC and 10.3AC. C7 shows around 6.95 volts but takes a minute to reach that on or off. Even off it holds at 6.95V. Looking top down, power switch has 5.06VDC center and top leg, on or off. 0VDC on bottom leg, on or off. Everything is cold to touch. Any advice is appreciated. Thank you!
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Posted By
BSZ
on 2025-08-01
15:02:02
| Re: Plus 4 Power issue No LED
Hello Dbrownlee!
C7 shows around 6.95 volts but takes a minute to reach that on or off. Even off it holds at 6.95V.
On the C7, this voltage seems low to me, but let's leave that aside for now; without the AC9V, the machine should start up without any problems. (Only the datasette will not work.)
Looking top down, power switch has 5.06VDC center and top leg, on or off. 0VDC on bottom leg, on or off.
That's strange.  If I understand your description correctly, you are talking about the three pins of the switch that are accessible from above. The "upper" pins are connected to AC9V. The +5V is switched by the "lower" pins of the switch. However, these are difficult to access for measurement purposes.
These voltages are suspicious! Are you sure the "C64 to Plus 4 square socket adapter" is properly wired? If possible, please take a photo of the connector and write to picture what voltage did you measure on which pin!
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Posted By
Dbrownlee
on 2025-08-01
18:52:34
| Re: Plus 4 Power issue No LED
Think I need to be a member for pics. But yes the lower switch legs. As the unit is in front of me, the switch is on the right hand side. I have a skinny probe on my meter. With the meter negative lead on a ground, I stick the positive lead in between the switch legs to the bottom rung. Middle measures 5.06V, as does the bottom leg furthest away. The close one reads 0V. On the power connector, I can measure that same 5.06V on the bottom two pins. The top two measure ~10VAC. I got the power adapter off of ebay from a seller in California. It has a reset button, if that helps identify it. The C64 to Plus 4 adapter came from a seller in Spain. I also have the original power supply but have not tried it for fear of it frying the unit.
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Posted By
Csabo
on 2025-08-01
20:26:31
| Re: Plus 4 Power issue No LED
You can always upload photos to any free image hosting site (like imgur.com) and post the links here.
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Posted By
SukkoPera
on 2025-08-02
02:40:38
| Re: Plus 4 Power issue No LED
I think your switch is broken, you should have +5V on the bottom right pin when it's on, IIRC.
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Posted By
BSZ
on 2025-08-02
06:30:17
| Re: Plus 4 Power issue No LED
Thanks for the photos, now I understand what you're measuring. Fortunately, the power connector wiring appears to be fine. Based on this, I also suspect a switch malfunction; we have encountered faulty switches before. After disconnecting the power supply, measure the resistance with the switch turned on, between the pins, which are labeled "5V" and "0v on or off" in your photo.
I also have the original power supply but have not tried it for fear of it frying the unit.
Your caution is understandable. Fortunately, plus/4 power supplies fail less often than brick-shaped C64 power supplies. Regardless, it's a good idea to use a modern equivalent instead.
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Posted By
Dbrownlee
on 2025-08-02
15:46:31
| Re: Plus 4 Power issue No LED
Thank you! I will investigate and report back, later today.
Update:
Does seem to be a bad switch. AC legs have continuity but DC legs do not. Anybody have a part number? Somebody has them on ebay but from Europe. Prefer U.S. And thanks for the help!
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Posted By
SukkoPera
on 2025-08-03
05:34:55
| Re: Plus 4 Power issue No LED
This switch was custom-made, it doesn't have any known P/N and you can't find it on the market, unless it's one that was recovered from a +4 board.
IIRC an Italian guy had some remade recently and was selling them on AmiBay. I think it was alex81, look for that.
Or maybe you can try this.
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