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View Full Version : XT 130W PSU 120V tp 240V conversion, is it possible?



mR_Slug
June 29th, 2017, 06:46 PM
I've been scouring modem7's site, and here for some info but still cant make heads or tales of it. Can you convert the XT PSU to run on 240V? Specifically the one with the P/N 1501436. I wondered if by '83 they built a dual voltage version, and its just a trace inside that needs to be cut?

paul
June 29th, 2017, 08:50 PM
If it's the same circuit as what's in the docs, you can, and it's easy if you're willing to get out your soldering iron. Here's what I PMed to one of our members last week and he reported success.
The schematic is here: http://minuszerodegrees.net/5160/psu/5160_psu_schematic.htm


Do all this on the "AC INPUT BOARD."

1. Break the trace at PL/SK102 pin 4. The right side (output) of that path will now not be connected to anything.
2. From the left side of that path (output of R104) connect a diode to provide power to PL/SK102 pin 5. So the diode points toward pin 5. Use the same diode type as in the 5150 conversion (1N5404 or 1N5408 ).
3. From the left side of that path (as above) connect a diode to draw power from PL/SK102 pin 3. The diode points away from pin 3.

The circuits around Z4 and RL101 look to be unaffected. It would be wise (but not essential) to replace C101, C104 with modern "X2" caps, same sizes but higher rating than 250, say 280VAC roughly. Replace C105, C106 with modern "Y2" caps, same higher rating. Big caps C1, C2, C3, C4 on the main board can be replaced at your option ... or if they look dodgy.

It might pay to first do a test. Disconnect PL/SK102 (the connector) and confirm that the voltage at PL/SK102 between pin 5 and pin 3 is ballpark about 325 VDC running via a stepdown transformer. After you do the conversion, check for the same voltage running off raw 230VAC, and verify that pin 4 is not connected. That way you don't risk the whole PS.

Dwight Elvey
June 29th, 2017, 08:52 PM
It is common for these supplies to have a jumper to select
between 120 and 240.
Usually it is converting the rectification from a doubling circuit
to a single wave rectifier.
You can verify if this can be done by measuring the voltages
on the large input capacitors.
Always do this by safely connecting the leads to the capacitor
with it powered down. The DC level on these capacitors is
clearly lethal.
Always discharge them after removing the power. The usually have
a bleeder resistor but these are known to go open, leaving
a nasty charge on the capacitor.
Tinker Dwight

mR_Slug
June 29th, 2017, 11:45 PM
Is this what you mean:
39405

I will have to crack open the PSU tomorrow and see if it matches the diagram. Sure looks simpler than the 5150 mod. That resistor installation is a work of art!
Thanks

paul
June 30th, 2017, 01:16 PM
Is this what you mean: That's correct ... and thanks :)

Note that there appears to be no fuse on the AC line, same as the 5170.
No idea why IBM left this out but be sure to check that the X2 and Y2 caps are suitably rated and in good shape.

mR_Slug
June 30th, 2017, 08:00 PM
Well it seems I must have an early version of the XT PSU. The AC input board only has 2 wires coming out of it to the main board. In fact that part of the PSU is exactly the same P/N 204-1076c. The main board unfortunately isn't just a beefed up version of the 63W PSU:
39419

39420

I have tried to decipher the main board and I think this is correct. (Resistor values are just placeholders):
39421

It looks like it may be possible to do a similar mod, but T5 is an issue. I can't work out what ratio it is, its labeled "eia 343 95-3601". I have been unable to power the PSU up on 120V as I cant seem to find my step-down transformer anywhere, very puzzling.

Anyway, I was thinking that perhaps I could disconnect the secondary side and run 240V through the tranny, then somehow come up with something to reduce the voltage down to the required voltage. Wont the voltage be doubled, and the amperage be halved? AFAIK it is immediately rectified, and there is what looks like a smoothing cap rated at 25V. I don't know that much about transformers, so I may have got this wrong. The alternative is to find a new transformer with the right ratio.

Am I going down the right path here?
Does anyone else loose large heavy objects, like transformers?

Dwight Elvey
June 30th, 2017, 08:15 PM
Can we see the bottom of the board with the transformer.
I what to see if it might have a center tap primary.
As it is, you can't do much with it.
Dwight

mR_Slug
July 1st, 2017, 03:02 AM
Sadly no center tap:

39430

I just remembered I have a huge box of wall-worts, maybe there's a transformer I could pull out of one of them. BTW, the two chips have date codes that are both early '83, indicating this is likely an early design of the XT PSU.

For reference:
221-234 PWM Regulator (8-40V, http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=221-234)
221-121 Voltage Comparator (2-36V, http://www.weisd.com/test/GenericParts_WEISD_view.php?editid1=221-121)

paul
July 1st, 2017, 01:26 PM
... run 240V through the tranny, then somehow come up with something to reduce the voltage down to the required voltage. Wont the voltage be doubled, and the amperage be halved? ... I don't know that much about transformers, so I may have got this wrong.
Am I going down the right path here?
No, don't do what you propose, please ;), you will burn it up. You should be able to source a proper 240VAC-to-whatever transformer once you know what the output is.

First, update your schematic covering the secondary side of T5. Then, power it up off your stepdown (carefully, please) measure the DC voltage across the smoothing cap on that output, I'm guessing it's around 25V. You might want to temporarily solder some wires to the relevant pads for measuring so you don't risk shorting something with the voltmeter probes while it's "live." After you power it down be careful of residual voltages on C14, C15 ... could be up to 162 VDC on each.

Next, update your schematic with any further items connected to the junction between the caps you have marked C14 and C15. Hopefully there's nothing else so you can change to full wave without further issues.

Dwight Elvey
July 2nd, 2017, 06:40 AM
If I'm making out the transformer correctly, there are only 4 leads.
So, no extra lead to be an input tap.
If you can't find your step down transformer, you can test the transformer
you have to see what its value is.
You have to unsolder it. Use one of your wall warts that has an AC output
and connect it to the primary. You can then measure the input and output
voltages. That will give you the ratio to apply to 120v.
Then you can hunt for a transformer that is close. Some of the wall warts
have transformers that are easy to rewind and aren't potted.
If you can find a small transformer that is for 240 and has a center tap primary, you can
use it as a auto transformer to drop the voltage. The core should weight about 1/2 the
T5 as it only deals with 1/2 the power in the core.
I did this once with a printer rated at 220-240 to bring it up from my 110-120v.
It is the other way but the principle is the same. I'd only use it on the T5 as the change of
the diodes is better for the raw input.
Dwight

mR_Slug
July 3rd, 2017, 06:43 PM
Ok well here is the updated schematic:
39469
39470

The voltage on my secondary seems to be 12VDC across the cap. The 11VAC across the transformer, is likely the result of my multimeter (1-2V accuracy). The third leg of pot R36 goes off to one of the chips. I tried to continue with the circuit diagram further but it gets real confusing.

So I guess I need to find a transformer that ~20:1. I suppose a 12VDC wall-wart should suffice.

Here is what I'm proposing to do:

As I understand it, R33, CR23 and R36 are there to provide a voltage drop to the third terminal of R36. For the moment I will take out the transformer, and in its place on the secondary side, connect 12V DC, from a wall wart. It's rectified, again giving 1.4V loss. But I would rather not desolder/solder, more than I have to. Correct me if I'm wrong but 1.4V loss isn't going to screw up the PSU is it? Alternatively connect 12VDC across the Cap and 12V between CR23 and CR26.

Then power the device, on 120V, and the 12VDC wall-wart. It this works, Perform the mod to full wave rectification, test, on 240V, then crack open the wall wart and try to somehow fit it in the PSU.

One thing I need to do first is mod my step down transformer. It's a tool transformer. For those of you who don't know about these uniquely British devices, they are wired to provide two 60V hot leads. The ground point is actually between the 120V. Fine for tools, but if powering a 120V computer and then you connect that computer to something else, that's also grounded, as I understand it you end up with a 60V difference in ground points! Somehow this hasn't been a problem when connecting a 240V monitor to a 120V PC, and I cant understand why? So I'm going to mod it to provide, float, 60V-60V and GND-120V.

Dwight, just to clarify, do you mean to use the auto-transformer arrangement ONLY if I cant find a transformer of the correct ratio?

Thanks for your help so far.

mR_Slug
July 7th, 2017, 01:20 PM
OK well I've made some progress. The tool transformer has been modified and is working. I've removed the PSU's transformer (T5), and done the full-wave rectification mod. I can now power the PSU from 240V with 12V being supplied to the secondary side of where T5 used to be.

I don't know why I didn't see it before but there are actually places left on the PCB for the additional diodes. See to the right of the connector, CR35 and CR34. Also just below the connector, the bridge W23 needs to be removed:
Before:
39555
After:
39556
Updated Schematic (red indicates changes):
39557

So this indicates that the board is designed with dual voltage in mind. So my question is now, can the existing transformer be used, and the secondary circuit be modified easily? Or was the intention of the designer to swap the transformer depending on whether the PSU was targeted for 240 or 120V?

If the existing transformer were used its now going to put out 24V, the smoothing cap is rated at 25V, but that seems a little close. This leads me to think the designer intended a transformer swap.

The transformer swap seems like the safest option. But I wondered if anyone more familiar with SMPS, would look at this (admittedly abstract) configuration, and recognize it? Or am I just chasing a ghost here?

Thanks

paul
July 7th, 2017, 02:10 PM
The transformer must be changed or another source of 12VDC maintained across the 470uF 25V cap. Yes, the designer intended a transformer swap. If you run that one off 240VAC it will fry in a few minutes! As Dwight said, you might find a suitable transformer inside an old (non-switch mode) wall wart.

Or look in Digikey (https://www.digikey.co.nz/products/en/transformers/power-transformers/164?k=transfomer&k=&pkeyword=transfomer&pv183=7075&pv1393=48&pv1393=78&pv1617=114&pv1617=96&pv1617=18&FV=ffe000a4&mnonly=0&ColumnSort=0&page=1&stock=1&quantity=0&ptm=0&fid=0&pageSize=25). You will need to measure the DC current used by your wall wart to supply this circuit to size the transformer.
Mouser (http://www.mouser.co.uk/ProductDetail/TE-Connectivity-PB/4900-9010RC62/?qs=sGAEpiMZZMvwUzoUXIIvybxvWcHlXqMIJJMreLPLlIY=) has a better selection. If you measure both the current and physical size it would be easier for us to help further.

Otherwise good work, and please maintain good electrical safety. Your work-site stepdown would have been better left with either a centre-grounded 120 VAC or even floating. But, you're past that point now.

Chuck(G)
July 7th, 2017, 02:36 PM
I thought the OP was using a tool transformer to step down 220 to 110 vac?

mR_Slug
July 7th, 2017, 05:01 PM
Thanks. Saved me chasing that ghost. I will first try to crack open the wall-wort I have. The one I'm using is a very common generic shaped one here in the UK, and feels like its not potted. If it will fit then it is an easy source for replacement transformers, in case anyone else wants to perform the mod.

I've wired the tool transformer to have the ground point switchable. There is float, 60-60V, and 0-120V. Usually the center point is tied directly to Earth. In the image below, I have made this switchable to set it so that instead the neutral of the 120VAC is now 0V with respect to earth. This is what you have in the USA right?

39572

I hope this makes sense. As I understand it the floating type is the safest when working on electronics, as if you touch only one place, you just ground it. Many of the ungrounded VCR's etc are just left to float, problem is when you connect, say an audio cable, between them and a grounded device you sometimes have massive potential differences. So I thought if you set the neutral of the transformer output to be at 0V with respect to Earth, your less likely to have things go wrong. Perhaps I'm missing something.

Chuck(G)
July 7th, 2017, 05:47 PM
Yes, you want S1 in the "up" position, but floating will probably also work.

US domestic home power distribution is 120-0-120, with receptacles and lighting wired on both sides, so "neutral" is grounded. Of course, for heating, air conditioning, cooking, etc. 240V is used.

Dwight Elvey
July 7th, 2017, 08:52 PM
This won't work. As Chuck just said, the neutral is grounded at the main fuse box.
If your unit puts a low impedance between the neutral lead and ground it will
cause a short on the lower half of the winding.
You are better to just leave the secondary float. It will make a safer system.
I see no reason to tie any lead of the transformer to ground. The socket
ground lead should be grounded.
Dwight.

paul
July 7th, 2017, 09:26 PM
Yeah, ideally your schematic should not show the link between N and G at the fusebox because it's not really relevant and confusing on first glance. Only the ground status after the power plug is relevant and I would agree that for troubleshooting electronics a floating output is best, as long as you become "aware" should you happen to touch one side, in case you carry on oblivious. 60-0-60 makes you fully aware of the initial mistake without potentially fatal consequences.

Chuck(G)
July 7th, 2017, 10:08 PM
I don't know how easy it is to dig into the tool transformer, but if you break the ground loose from the center tap on the 60-0-60 winding, you should be able to connect it to the neutral (ground) on the 240V side. But that ground sitting at 60VAC will probably raise all sorts of problems. So, absent that, float the output with no ground.

mR_Slug
July 8th, 2017, 05:35 PM
Ok well I can see why that diagram was confusing. In the center switch position "isolation mode", it also removes the protective earth. Not a good idea! This is what I've actually done:

39630

Originally the center tap on the secondary side, was tied directly to earth, giving 60V on both The L and N coming out. So I cut this connection, and added a switch, S1, in the configuration shown.



+---------------+-------------+-------------+
| | 240V side | 120V side |
| | L N E | L N E |
+---------------+-------------+-------------+
|top position | 240V 0V 0V | 120V 0V 0V | (same as USA)
|middle posiion | 240V 0V 0V | ?V ?V 0V | (floating)
|middle posiion | 240V 0V 0V | 60V 60V 0V | (original)
+---------------+-------------+-------------+



If your unit puts a low impedance between the neutral lead and ground it will cause a short on the lower half of the winding.

I assume you mean the original 60V-0-60V configuration?


...if you break the ground loose from the center tap on the 60-0-60 winding, you should be able to connect it to the neutral (ground) on the 240V side. But that ground sitting at 60VAC will probably raise all sorts of problems.

Yes if the center tap of the secondary is connected to the neutral side of the of the 240V this will cause all sorts of problems. If center tap of the secondary is connected earth, and earth is connected to the neutral at the fuse board, then essentially you have the same circuit, no?

Leaving it to float, is an option, but isn't the 120V-0V configuration effectively the same as a US outlet now?

The PSU:
I have cracked open the wall wort and it is a little more complicated than I though. I will post back with some info soon.

Thanks for all your help.

Chuck(G)
July 8th, 2017, 05:51 PM
Yes if the center tap of the secondary is connected to the neutral side of the of the 240V this will cause all sorts of problems. If center tap of the secondary is connected earth, and earth is connected to the neutral at the fuse board, then essentially you have the same circuit, no?

Leaving it to float, is an option, but isn't the 120V-0V configuration effectively the same as a US outlet now?

You don't want the center tap connected to anything. But yes 120-0V with the 0V connected to the ground lug--and earthed, is essentially the US system. Remember the US distribution:

120-0-120, with the 0 also earthed. The 0 side is the wider of the two prongs on a USA plug--don't get those mixed up. So the wide prong in US outlets is connected to 0, with the 3rd ground prong earthed--usually, the two are connected together in the breaker panel. The narrow prong on the US plug is connected to 120V; it doesn't matter which side of the distribution transformer winding.

US electrical code requires an independent conductor for the grounding prong, even though it may be connected to the neutral side of the line in the breaker (distribution) box. Safety is provided by a GFCI (if the fault circuit interrupter detects that the current between the two flat prongs isn't the same, the circuit is interrupted.) So, tossing a hair dryer into the bathtub will cause the (now code) GFCI to trip, regardless of what the TV murder mysteries say.

240V appliances are a different matter. An electric oven may have 4 conductors; two for the 240 heating elements, one for the 120V to run the clock and controls and a fourth for earthing the body of the oven.

On the other hand, my table saw is 240V with only a protective ground wire--but that requires a special circuit.

I do envy you fellows in the UK. Here in the US, the most powerful home vacuum cleaner available is a paltry 1440 watts. Code requires that a portable device (i.e. something that's not wired in) to draw no more than 80% of the circuit capacity. Since a lot of US homes are still wired with 15A, 120V outlets, the maximum current draw allowed is 12A.

paul
July 8th, 2017, 08:36 PM
...This is what I've actually done:

39630
Frankly I see no need for a grounded neutral option as no appliance expects that or even cares. The centre ground is the best safety option (obviously why it's used for worksite tools) and the floating output could be useful for some advanced troubleshooting.

Chuck(G)
July 8th, 2017, 09:35 PM
It depends on what other gear you have hooked to the 120V supply. There are some bits of vintage equipment with a so-called "hot chassis", where one side of the line is connected to chassis ground. This would create a bit of a problem if the protective ground (connected to the case) were at 60VAC.

Look, it's a North American convention; best to follow it, no? You don't take a UK 240V piece of equipment and place the protective ground prong at 120VAC, do you?

paul
July 9th, 2017, 01:54 PM
I would guess that that 60 V is safer than placing the hot chassis at 120VAC. (Thankfully 5-valve radios in 240VAC countries have power transformers and a grounded chassis.)

The output of a portable power transformer is not house wiring and a technician can do whatever he or she feels is appropriate for troubleshooting purposes.

I've also seen the 110 VAC Center Tap Earth (CTE) standard used in industrial PLC I/O ... in the US auto industry.


...You don't take a UK 240V piece of equipment and place the protective ground prong at 120VAC, do you?

Hmm, sorry, Chuck, no one is suggesting placing the protective ground prong at 60 V. Ground is still grounded.

Chuck(G)
July 9th, 2017, 02:41 PM
I guess I'm not following the conversation well, then. I see the low end of the 120V "neutral" and then I see the ground prong (chassis ground) hooked to the center tap (60V above neutral) US convention is neutral-ground.

I'm wondering if the setup will create issues with ground loops. Maybe I'm fussing about nothing.

paul
July 9th, 2017, 04:20 PM
Yes, mR_Slug's wiring diagram is slightly misleading schematically, functional but not ideal if it's really wired that way.

I just opened up my 1KVA NZ worksite transformer and the 110 VAC output is completely floating. I've run my US-sourced laser printer off it for the last decade.

Home wiring is going to protect against overloads and subsequent fire as a first priority and a grounded neutral is a practical standard so ground faults off Line cause a trip.

Work site power tools, and I would argue technical troubleshooting, would favor safety first so the output with a locally-grounded center tap is a good choice. Completely floating outputs have the disadvantage that you don't know you touched one side until you touch the other side, at which point it is a bit late. On a work site, cutting through a power cord could still trip the fuse/breaker and in any case with a center tapped ground, minimise the potential shock hazard.

As for ground loops, I don't see how the relative potential of the incoming AC would affect that, as long as the isolation is from a nearby transformer and does not pick up further potential capacitively, if completely floating. Of concern is the dielectric rating of the input electrics over chassis ground. You wouldn't want a floating AC input float >400V over ground because it may exceed component dielectric ratings. A center-tapped ground should not affect the functionality of any modern appliance or electronics since the AC input is fully isolated from the chassis.

3964839651 pardon the rotated photo, couldn't seem to correct it

mR_Slug
July 11th, 2017, 07:52 PM
Ok, finally got some time to play with this again. The first wall-wort I took apart turned out to be a SMPS, I always thought they were all linear. The second would fit, but due to the terminals for one winding being on the top and the other on the bottom it was going to be very difficult to mount it.

I was going to measure the milliamps, but I realized my meter cant do that. It's a clamp-on thingy, intended for electricians. It is made by toolzone, so I doubt an actual electrician would buy one. As the probes were broken, and tape holding on the battery compartment fail again, I've ordered a new multimeter.

I did measure the resistance and got 7.8K which should equal 15mA. But I don't know how accurate that is, or if it's completely meaningless. I had a look around for small transformers and found this:

http://www.ebay.co.uk/itm/VIGORTRONIX-VTX-120-003-606-TRANSFORMER-3VA-2-X-6V-/171948239506?epid=1827115810&hash=item2808e9ea92:g:rfAAAOSwcwhVNX3A

datasheet:
http://datasheet.octopart.com/VTX-120-003-606-Vigortronix-datasheet-10380009.pdf

Says its rated at 250mA, and aside from the dual primary and dual secondary, as far as I can tell it looks like it will fit the original PCB holes. I can just connect the two 6V windings, and the two 120V windings and get a 240V to 12V transformer right?

paul
July 11th, 2017, 08:35 PM
Looks close enough to try out.

Dwight Elvey
July 11th, 2017, 09:21 PM
I'm looking at the drawing, if the switch is set so that the external ground
is connected to the sockets neutral, the ground on the plug will be at
60 volts.
Most equipment connect that to the physical chassis.
If one set that on a grounded surface, it would short out the 60V output of the transformer.
I would not wire it in such a configuration.
I see no big issue with grounding the center tap but the circuit as drawn
is really dangerous.
Dwight

mR_Slug
July 11th, 2017, 10:52 PM
Took me a while to understand what you mean. Unless I have missed something you must be referring to the first diagram I drew in post #18. Yes the diagram in post #18 is very very wrong. I have updated it in post #20.

On second thoughts, would it not make more sense to bond the neutral of the 120V to the neutral of the 240V?

Like this:
39695

Also, I changed the typo in the thread title, by editing the post before anyone else posted. I'm sure it updated. It seems to have reverted to "tp", confusing?

Dwight Elvey
July 12th, 2017, 06:32 AM
I didn't notice the changed diagram.
The only issue is that most switches on the power supplies
only switch the hot lead.
If someone though turning it off at the switch was enough to
poke around, a screwdriver or a ring on ones hand could find
the 60V to ground.
I do like the idea of the balanced voltage for other safety reasons.
One could still manage to kill them selves with 60V but it is
safer, as you mention.
Dwight

paul
July 12th, 2017, 01:30 PM
On second thoughts, would it not make more sense to bond the neutral of the 120V to the neutral of the 240V?

Like this:
39695

Umm, no. Like any other modern appliance, treat the Neutral on the incoming 240VAC as though it is "hot" because it's potential is not entirely certain. You might encounter a reverse-wired plug or overload at another point in the household circuit where that current raises the potential on N. Same reason why 240VAC appliances often switch both sides of the mains.

On your schematic you need to remove the link between the incoming N and ground since that link is not part of the transformer assembly wiring between it's 240VAC plug and the two outgoing sockets. I also note there are no fuses and you might check to see if the transformer core is tied to ground as well.

Dwight Elvey
July 13th, 2017, 01:35 PM
Umm, no. Like any other modern appliance, treat the Neutral on the incoming 240VAC as though it is "hot" because it's potential is not entirely certain. You might encounter a reverse-wired plug or overload at another point in the household circuit where that current raises the potential on N. Same reason why 240VAC appliances often switch both sides of the mains.

On your schematic you need to remove the link between the incoming N and ground since that link is not part of the transformer assembly wiring between it's 240VAC plug and the two outgoing sockets. I also note there are no fuses and you might check to see if the transformer core is tied to ground as well.

In the house we bought about 3 years ago, 20 percent of the sockets
had neutral and hot swapped.
Only 5 of them actually had the ground terminal connected.
The seller recommended the contractor he'd been using. I asked
if he'd upgraded the sockets to ground lead sockets.
"He did a good job, didn't he!"
was the response.
Dwight

mR_Slug
July 16th, 2017, 06:20 PM
Well I got the new transformer. I folded over the pins, and soldered the two 6V windings together and did the same for the two 120V, giving a 240-12V configuration. Then I lightly touched one of the other pins, and it broke off immediately. So I managed to solder on a lead further back where the winding connected to the pin. It turned out that my measurements were wrong, and I needed to drill 1 new hole in the PCB. So anyway I did all this, got it all soldered in, was very pleased with myself, patted my self on the back, until I realized I'm an idiot.

The negative side of the transformer doesn't connect directly to the negative coming in. It DID previously, but because I had removed the W23 jumper, now it just connects to the center of the two main caps. No one could have advised me of this, because my schematic was incorrect.

So my intuition on reusing the 120V transformer was right, but my schematic tracing skills need more work.

Anyway the end procedure is really quite simple, remove W23, solder in diodes at CR34 and CR35.

Updated schematic
39840
So now back to the filtering board. I can order some 0.1uF X2 caps, but would .22uF X2 275V work? I seem to have some left over from anther project, and I'm itching to get this finished.

Tool transformer:
Yes it does have fuses and switches, I just didn't add them to the diagram to make it simpler.

paul
July 17th, 2017, 12:47 PM
I can order some 0.1uF X2 caps, but would .22uF X2 275V work?As long as it's marked X2 it should be fine.

mR_Slug
August 5th, 2017, 06:55 AM
Just an update. Finally got around to testing this with my actual XT. Everything is working perfectly. Thanks to everyone who helped.

nztdm
December 15th, 2018, 10:38 PM
Just an update. Finally got around to testing this with my actual XT. Everything is working perfectly. Thanks to everyone who helped.

Hello
I want to do this on my own XT PSU.

I found a couple errors on the final diagram. The diagram didn't show W23 connecting between C14 and C15.
This one has some fixes.
My board is -03 , not -01, but they are probably the same in this regard.

Could I get a run-down of what you did exactly? I find it unclear.

-Install diodes CR32 and CR33
-Remove jumper W23
-Replace T5 (115/12) with 230/12 one that fits

And by my guesses on the filter board:
- Replace X2 caps with 275V+ rated ones.
- Replace 300K resistor on filter board with 560K resistor.
- Replace 4A fuse with 2A fuse.

Thanks
JD

nztdm
December 17th, 2018, 12:25 AM
I've successfully done this conversion on a 5160 PSU of mine.

My board was the -03 version instead of your -01 version, but it's nearly identical.

Exact procedure, to clear things up:

Parts list:
- 2 x 1N5408 diodes
- 1 x 10ohm 5W resistor
- 1 x 560K 1W resistor
- 1 x 2A 250V 3AG-size fuse
- 2 x 100nF 275VAC+ "X2" film capacitors
- Torx T10H security-bit screwdriver
- ~7mm nut driver

Procedure:
- Install two 1N5408 diodes at CR32 and CR33 empty holes. (May need to drill holes slightly bigger)
- Remove jumper W23 next to J3.
- Replace R1 (2ohm 5W) on the relay board, with a 10ohm 5W.
- Replace the main fuse (4A 250V 3AG-size) on the AC-input board, with a 2A 250V 3AG-size one.
- Replace the 300K resistor on the AC input board, with a 560K 1W.
- Replace the two X2 capacitors on the AC input board, with ones rated 275VAC or higher.

Test that you still get between 9 and 12 V AC on the secondary of T5 when mains is applied.
A test load is needed to test the power supply. One 3.5" drive was not enough for me. A 5.25" drive was. Maybe two 3.5" would be.

BE CAREFUL!

49957

Also, with Paul's help, I've successfully done a late model 5150 PSU too (that differs to the one in Paul's 5150 PSU guide), and will post my findings in another thread I guess.

Cheers
JD

Note: I plan on removing my previous reply, but I cannot as I am too new to the forum.