B-Series Power Supply Transformer

[crock]

Good afternoon Gentlemen,

Does anyone know the specs of the original power transformer in the low profile b-series machines PSU?

I have a very beaten up Commodore 610 (B128 ) which has been modded to 256k at some point in the past. I am also assuming it’s spent time in the US or some other 115V supply country, as the power transformer in the PSU has been replaced with a dual output 117 VAC -> dual 1.9A, 16 VAC one. This looks like a home brew mod as part of the aluminium PSU chassis has been bent downwards to create a mounting flange for the transformer.

I would then appear that the item found its way back to Europe as the PAL link has been installed and an additional 230->117VAC transformer has been strapped to the underside of the air vents in line with the mains supply.

This has resulted in a rather untidy (and dangerous) mess of mains wiring inside the case which includes taking the mains switch out of the circuit, connector blocks and insulating tape. I’d like to take it back to something approaching its original state and want to put a 230 VAC power transformer back in the PSU but I can’t find any details regarding the rating of the original transformer in the European B-series machines.

A dual 16V, 1.9A output would seem about right given the C610 (and I assume the B128 ) were rated for 60watts, but I cannot find such a rated transformer on ebay, digikey or maplins. Given it’s a switcher, I want to know whether there is any scope for replacing this with an alternative transformer with dual 14 or 18VAC outputs.

Cheers, Rob

 

[carlsson]

If I can remember, I can look inside my 610. Should it explicitely say which voltages and amperages it outputs, or is that more a matter of measuring it?

 

[crock]

Thanks Anders, I don't mind, the stated V & A is great if it's there. My EU 610 doesn't say on the transformer but some might.

Rob

 

[crock]

I finally got fed up with the original power supply and replaced it with a small form factor ATX PSU I grabbed off ebay for £11. I figured this was a bargain as this model (FSP150-50PL) retails for around £40.

The PSU supplies the +5V, +12V and the -12V required by the b-series (in my case a 620) but not the 50hz square wave required to drive the TOD line. I found out that unlike the 64, the b-series will not boot if the TOD signal is not present. I solved this with a 50hz signal generator circuit using a programmed PIC from Elm electronics http://www.elmelectronics.com/ebench.html#ELM446 .

The power switch has been replaced by a switch grounding the power-on line from the PSU. Molex made the power connectors in the b-series and as luck would have it, the pitch of the pins matches those used in the old IDE power connectors used on hard drives. A number of old IDE to SATA adapters were sacrificed to extract the male pins used to plug in to the 620 main board as shown, along with liberal quantities of heat shrink.

Finally, ATX power supplies often have a minimum load otherwise the built in safety cut-out will trip. This PSU expected a load on the 3.3v line to prevent it cutting out, so there is a 33ohm power resistor in line to draw a small 0.1A load. This was lower than I expected so if you try this, you may find a lower resistance load is required, which may in turn need heat-sinking.

My final task is to fashion a suitable bracket to hold it inside the now much emptier case!

Any questions, please ask!

Rob

 

[Pet Rescue]

Crock if you look on the forum under my b series thread, I posted a picture of the transformer with part number and voltages label.

Mine was a 256 prototype so I don't know if it's any different!

 

[carlsson]

Alas, this is yet another case when something I promised just evaporated in the middle of other things I'm doing. I may get to have a look within this month, but as you already found a replacement and Pet Rescue posted a picture from a prototype model, it may not be cruicial to look at the PSU of the production model.