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General Chat / Re: What did you buy today? Post your latest purchase!
« Last post by Falkra on Today at 10:46:49 pm »
  ;D

I don't like the leads/probes, I'll use better ones I have.
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Not sure if this is well known The Boat Anchor Manual Archive
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Buy/Sell/Wanted / Re: Wanted Keithley 2000 Scan-Card
« Last post by hellzakk on Today at 10:46:32 pm »
pm sent
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Buy/Sell/Wanted / Re: Lots of gear from "GrandPa's Lot"
« Last post by Inverted18650 on Today at 10:46:14 pm »
Are any of the 3456A's still available?

Indeed there are, how many do you need?
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The issue with the resistor overheating is due to the device under test being at a high voltage, relative to earth. The main advantage of the capacitor is the device being tested can float at any voltage, up to the capacitor's maximum rating.

Shaver transformers are normally rated at about 20VA, although they won't be rated to that continuously. Dual voltage operation is standard. The one in my house has separate sockets and a mechanism which ensures only one can be used at a time. I haven't taken it apart, but I'd expect it has two 120V secondary windings and a switch to select between series and parallel configuration, depending on whether the 240V or 120V socket is used.

I had a quick search for 25VA isolation transformers.
Triad VPS230-110
Available from Mouser and Farnell. Lookst good, double bobbin and low capacitance.
https://uk.farnell.com/triad-magnetics/vps230-110/transformer-2-x-115v-25va/dp/1610413
https://www.mouser.co.uk/ProductDetail/Triad-Magnetics/VPS230-110?qs=%252bfhPKvh1fqM%2fIMKduQ8CRw==

Triad VPT230-110
Toroidal. Probably higher capacitance, but will be more efficient. US stock so available from Farnell at high cost or Mouser, with a long lead time.
https://uk.farnell.com/triad-magnetics/vpt230-110/transformer-toroidal-2-x-115v/dp/1785731?gclid=EAIaIQobChMIlZq7ypjy3wIVqrftCh2WqQLMEAAYAiAAEgL2sPD_BwE&mckv=s4rYYLzOH_dc|pcrid|99299485688|kword|vpt230-110|match|p|plid||slid||product||pgrid|5285736368|ptaid|kwd-24784252128|&CMP=KNC-GUK-GEN-SKU-MDC
https://www.mouser.co.uk/ProductDetail/Triad-Magnetics/VPT230-110?qs=wkKrz7WmEgNNNgyT8w4YqA%3D%3D&gclid=EAIaIQobChMIyMfwz5Hy3wIVo7XtCh3yIQbZEAAYASAAEgJLFPD_BwE

Bel Signal A41-25-230
Similar to the first one. Available from Digikey and Mouser.
https://www.mouser.co.uk/ProductDetail/Bel-Signal-Transformer/A41-25-230?qs=sGAEpiMZZMvwUzoUXIIvyZ8riR3Pta28%252b8Y6KbSbVRk%252bKxx4UgnHTw%3d%3d
https://www.digikey.co.uk/product-detail/en/signal-transformer/A41-25-230/595-1303-ND/953173

Another possibility is to buy a cheap shaver socket or salvage one from a skip and take the transformer out of it. Some are cheaper than buying an isolation transformer. The only issue is whether it will be able to power the SMPS continuously, without overheating.

https://www.tlc-direct.co.uk/Products/PU8900.html?source=adwords&ad_position=&ad_id=315107931576&placement=&kw=&network=u&matchtype=&ad_type=&product_id=PU8900&product_partition_id=297072075353&version=finalurl_v3&gclid=EAIaIQobChMI7dGoqZry3wIVDJztCh1ErAEjEAQYBCABEgKNE_D_BwE
https://www.directtradesupplies.co.uk/product.php/193005/ansell-dual-voltage-shaver-socket--white-?gclid=EAIaIQobChMIwImru5vy3wIVRofVCh0nzwF8EAkYASABEgJrgfD_BwE
https://cpc.farnell.com/unbranded/701875/shaver-socket-dual-voltage-white/dp/PL15991?mckv=sKmngMpNY_dc|pcrid|224681503328|kword||match||plid||slid||product|PL15991|pgrid|47203068935|ptaid|pla-559841591210|&CMP=KNC-GUK-CPC-SHOPPING&gclid=EAIaIQobChMIiejRrZvy3wIVSrftCh18vghaEAkYDiABEgJ95fD_BwE

Regarding dual voltage operation: I don't see any issue with having a jumper or switch. How often are you planning to take it abroad? A 1:1 230V transformer will work, but bear in might the current draw on 120V will be greater, so a 230V transformer running on 240V will only have half the VA rating. The power factor of the SMPS might also be poor, so even if it only uses 10W, it still might need a 20VA transformer.
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Buy/Sell/Wanted / Re: Lots of gear from "GrandPa's Lot"
« Last post by Inverted18650 on Today at 10:45:03 pm »
Hoping its a bit more like this!
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Buy/Sell/Wanted / Re: Lots of gear from "GrandPa's Lot"
« Last post by gnavigator1007 on Today at 10:40:05 pm »
Are any of the 3456A's still available?
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Repair / Re: C-64 Weirdness.
« Last post by CJay on Today at 10:39:23 pm »
No, it's the other way around.

"In all C64 models VIC-II is socketed for easy replacement, but it is important to notice that 6569, 6572, 6573, 6566 and 6567 use 12 volts and 5 volts when 8565 and 8562 use only 5 volts. Replacing old version with new version without motherboard modification destroys 8565 and 8562 if powered up in the oldest versions of C64 motherboards."

Best is to measure Pin 40 to ascertain the voltage present there and determine the model.

Umm, I thought that was what I said?
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usb on a 1.6mm thick board always calls for crazy thick traces, instead focus on keeping the distance you need to route your USB lines short, this way you dont need to worry about impedance anywhere near as much,

you can reduce how much trace width you need a bit by routing a picketed ground along side the differential pair. (coplanar Wave differential pair, its not in any free tool I have seen, but you can use it to trim down your Zo)

If you want to follow the spec as close as possible, 0.18mm gap, 0.8mm trace, 0.8mm gap to ground, yes it is crazy sized, and near to the ratio limits, but if you want close to 90 diff, 50 Zo, then that should put you inside the limits.

A good tool for this is "Saturn PCB Toolkit"
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If you can - Use a 0.8mm PCB instead of 1.6mm, that will make it easier to approximate the 90 Impedance - Use as thick traces as possible, and be aware that if you let the ground pour on the top layer get too close, it will also alter the impedance
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