Dead commodore 4040 disc drive

[pudwink]

Hi all
Following on from my commodore pet computer I would like to get the 4040 disc drive working as well.
I found a recent post on here for the same drive and as in that one I found no voltage at CR7/8/9 on the main board but unlike the previous post the wiring looks fine although onthe bottom of the transformer there is the earth neutral and live going in but there is a red snipped off wire next to them but is this for 110v?.
The fuse and switch test fine I would like to test for voltages coming out of the power supply to the motherboard but dont know what each wire is.
Any help as always is much appreciated.
Many Thanks

[TonyDuell]

I'd start with some DC resistance tests -- using the normal ohms range of your multimeter -- with the unit unplugged from the mains.

The tags on top of the transformer are almost certainly the secondary windings as they are connected to the logic board. It looks to be a pair of orange wires, a pair of red wires, and one other (black). This suggests a simple winding with 2 wires and a centre-tapped one with 3.

With the connector unplugged from the logic board (as in your photo) and the unit unplugged from the mains :

Measure the resistance between the 2 orange wires, should be a few ohms I would think.
Ditto between the 2 red wires.
Now test from the black (?) wire to each of the others. I would expect a low resistance to either the red ones or the orange ones.

Now, still with the connector unplugged from the board, turn on the power switch (mains plug unplugged from the wall) and measure the resistance between the live and neutral pins of the mains plug. This circuit consists of the mains cable, the switch , the fuse, and the mains transformer primary winding. The resistance will be a bit higher, maybe even a few thousand ohms, but it should not be 'infinite', a total open-circuit.

[pudwink]

Hi
I have done what you suggested using continuity setting on my multimeter and get a beep and .4 or .5 ohms.
But when I try testing across the plug I get nothing just O/L.

[SiriusHardware]

The secondaries (the windings on the low voltage side) will be very thick wire so the low resistances you see for Tony's tests may not be unusual.

Picking up on what you said earlier, the snipped red wire...

It's not too obvious where that is on your original picture so could we have a closer shot of that snipped wire and also shots of the wiring on the other side of the transformer and the general area around where the mains wiring comes in, the on-off switch, the fuse holder, the mains filter if there is one - that will be a metal can with 4 wires going to it, probably two blue and two black, if it is fitted.

[ScottishColin]

For reference, here's the transformer area of my working 4040, although it looks different to the OPs.

Happy to take any readings or any photos here to help if I can.

Colin.

[pudwink]

Hi
Here is mine showing the red wire.

[buggies]

Originally Posted by pudwink

Hi
I have done what you suggested using continuity setting on my multimeter and get a beep and .4 or .5 ohms.
But when I try testing across the plug I get nothing just O/L.

The transformer primary resistance could be in the region of hundreds of ohms so you would need to use the DVM on resistance mode not continuity.

[SiriusHardware]

Hmm, surprisingly different from Colin's. That red stub will most likely be the 220V tap so, assuming your drive unit is a 220V-240V model - does it say so on a label on the unit? - you don't need to worry about it except for the fact that that tiny stub of metal sticking out from the end of the red insulation will have high AC voltage on it when the unit is powered. I would put some close fitting heatshrink over the end of that to make it impossible for anyone to come into contact with the core of the wire.

Wire colours black and white are 'American' for live and neutral respectively, it doesn't look as though the unit has a mains filter to complicate things, unlike Colin's.

All measurements and actions below to be carried out with the mains plug UNPLUGGED from the mains, I'm sure you know that, but we have to consider the possibility that someone we don't know could read this thread in the future and follow these instructions literally.

First of all verify that both fuses are OK, the one in the fuse holder in the unit and also the one in the mains plug - both should show continuity, obviously. While checking the fuse in the mains plug also check that the screws on all three pins are really tight, as it is very common for them to work loose over time.

As buggies said, you need to measure the resistance between live and neutral on the plug rather than looking for continuity, and of course the drive unit's mains switch needs to be in the ON position during that measurement. I seem to recall that the primary of Colin's transformer had quite a low DC resistance, in the order of tens of ohms.

[pudwink]

Hi
On the back of the drive it just says 240v I have tried the lead again and getting nothing I then plugged it in to something else and tried the test and got a reading so the lead is fine.
Many Thanks

[SiriusHardware]

Still with the plug unplugged from the mains and the unit's mains switch in the ON position, can you measure the resistance (not continuity) between the following two pairs of points:

One side of the mains switch to the live pin of the mains plug, resistance is?
The other side of the mains switch to the neutral pin of the mains plug, resistance is?
One side of the mains switch to the other side of the mains switch, resistance is?

(If the mains switch has three pins, use the ones which have wires going to them as one side of the switch / the other side of the switch, ignore any third (unconnected) pin.)

From what you have said, can I take it the mains cable plugs into a socket on the unit's rear panel, like the one on a kettle or similar?

[pudwink]

Hi
May have had an eureka moment yes the back socket is a kettle type and what I have tried is taking the readings from the back of the socket and I get the readings I then checked for continuity from the socket pins through to the wiring on the back of the socket and only getting continuity on the earth nothing on the live or neutral.

[pudwink]

Hi
Looking into it these sockets have two rifa caps which as usual produce the magic smoke.
Does anyone know where I can get a replacement from as I don't think it will be possible to take it apart.

[pudwink]

Hi all
I have found this one it's 15a not 3a like the one fitted but would it be ok as a replacement.
https://www.ebay.co.uk/itm/185419110...MAAOSw9OZieWyz

[Mark1960]

Will that one fit? It looks quite a bit longer. Also you need to know if it matches the cut out in the case.

You might not need the filter, you could remove the filter and connect mains directly, just to confirm thats the only fault before you start spending any money on parts.

[pudwink]

I did wonder if that would be possible to wire it up without a filter.

[SiriusHardware]

How are the outgoing wires from the original filter connected to the filter, by solder terminals, by shrouded push-on spade connectors, or do they sprout directly from the body of the filter, or...?

Also where is the mains fuse on the UNIT, is it a separate chassis mount fuse holder or is it built into that filtered socket?

[pudwink]

The wires are soldered on with separate switch and fuse.

[SiriusHardware]

Measure the resistance between the black and white wires soldered to the filter, first with the unit mains switch turned OFF, then with the unit mains switch turned ON. What resistances do you see?

[pudwink]

I get nothing with the mains switch off when turned on in continuity mode I dont get a steady reading its up and down but when it settles down a bit its between 20 and 45.

[pudwink]

Just tried it again and now it settles at 14.9