Previously, way back in August 2016, I posted about having power supply problems on my Sega TeraDrives.
I had considered falling back onto a PSU replacement if replacing parts blindly failed. As it turned out this was the plan I ended up following. However, instead of the PicoPSU, I ended up going with the Mean Well RD-65A power supply. Ronnie of ASSEMblergames went with the Mean Well PT-65B for his own TeraDrive, which is great for certain old ISA cards as they require a negative voltage rail.
Leading up to this though, I had replaced a whole heap of components on the PSU. I finally received the last components I was waiting on (C3331 and M5237L) and threw them into the pile of bits to fit alongside B1274. The bad news, it didn’t work. The good news, even more fault was detected. It seems as though the power supply was having issues getting enough juice through quick enough.
The non-funcitonal unit was showing the values below (under 0629). At first I thought I had a no-power situation – it was close. Leaving the PSU connected for around a minute allowed it to charge up and then push through insufficient power… to do nothing. I did notice that the 12V rail with no load was jumping between 10.9x and 10.3x every few seconds, while the 5V rail remained steady.
1135 – Working (Reference)
12V rail (yellow cable) – no load 11.46V
5V rail (red cables) – no load 5.00V
12V rail (yellow cable) – under load 12.16V
5V rail (red cables) – under load 5.17V
0629 – Non-functional
12V rail (yellow cable) – no load 10.93V
5V rail (red cables) – no load 4.93V
12V rail (yellow cable) – under load 12.12V
5V rail (red cables) – under load 4.75 – 4.84V
=========================================================================== C6 330uF 200V 105°C H=31mm W=22mm "Rubycon" C7 4.7uF 350V 105°C H=16mm W=10mm C9 47uF 50V 105°C H=11mm W=6mm C12 1000uF 35V 105°C H=22mm W=12mm C14 1000uF 16V 105°C H=16mm W=10mm C16 6800uF 10V 105°C H=37mm W=12mm "Nichicon VZ(M)" C17 3300uF 10V 105°C H=22mm W=12mm "Sanyo" C19 10uF 50V 105°C H=11mm W=5mm C21 10uF 50V 105°C H=11mm W=5mm IC2 M5237L TO-92L Q1 2SK723 Q2 B1274 Q3 C3331 ===========================================================================
That was enough tinkering for me though, especially with mains voltage, so I decided to terminate the Sega TeraDrive PSU repair and pass the units on to other folk. Not with a bang but a whimper. Above is a listing of the major capacitors and some other components on the PSU mainboard.
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