Agilent E3610A - Shorted transformer? - Page 1
Forum section: electronics / beginners

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 12:28:31 am
content: So, I found a not-so-cheap-but-cheaper-than-usual E3610A for sell.I got it. Received it today. The seller informed: Turns on but immediately blows the fuse.So I oppened it up and started testing some components and nothing got my attention. I started suspecting the transformer (wich was my biggest fear). Since I didn't have any 2A fuse around, I decided to put a 500mA fuse instead. I removed CR2 wich is the bridge rectifier for the main output and tuned it on.The fuse blows.So I decided to remove the internal fuses for the refference bias supply F1 and F2.The fuse blows.So I decided than to remove F3 wich is the fuse for the display.The fuse blows.So, I guess I already know the answer, but: is it shorted or is there anything else I can try and check?Since it's a very good power supply, I'm willing to try to get it to work again. I've been thinking about getting one or more transformers and hooking it up to the supply. I do have a 12v transformer laying around, wich is something. maybe I can get it to work for the bias and display part.I would need to know the voltages for the taps on the original transformer do that I can try something. I supose the output tap would be something close to 15V, but I can only find 12V or 24V on the market here.So, is it worth making a frankenstein out of this power supply?Here's the link to the schematic, but I imagine some of you already know it by heart hahahttps://www.manualslib.com/manual/1342113/Hp-E3610a.html?page=16#manual

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 01:41:20 am
content: Sounds like a primary winding issue . Check that there is no shorting on the power cord . Remove plug from power outlet and check for continuity between L ,N and Ground of power cord with switch on .Check for continuity between primary and secondary windings .Check power switch for shorting .

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 02:15:43 am
content: Quote from: Jwillis on October 06, 2021, 01:41:20 amPower cord is ok. It's actually a cord I use on a laptop charger. The supply came with no power cord. But I double checked it and it's ok.L,N not measuring any continuity between them unless main switch is on. Ground measures no continuity to any of the other two terminals.Also found no continuity between primary and secondary.

author: andy3055
author_rank: Super Contributor
timestamp: October 06, 2021, 02:45:49 am
content: With the 3 fuses and CR2 out, if it still blows F4 fuse, did you check C1 that is still in circuit? Could it also be that the 500 mA fuse is too small for the no-load current?

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 02:51:06 am
content: Ok. So it sounds like a shorted primary coil . Have you tried putting an incandescent lamp in series with the Live wire . Search on the internet for " incandescent current limiter". Great diagnostic tool for transformer issues and easy to build . If the light glows brightly then the Primary winding is indeed shorted. And it won't keep blowing your fuses.You can use individual transformers to replace the burned out one .The display transformer can be 12V if that all you have available .The reference and bias can use a 12V 12V-0V-12V center tap since it regulated down to +12V and -12VThe last transformer is use purely for current . You could probably get away with a 12V-0V-12V high current but I'm not 100% sure about that .

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 06, 2021, 02:56:40 am
content: The obvious one:Are you sure it is the correct voltage transformer? They are not selectable. A 120v device on 240v mains?Some labels have both voltages with a black marker check in the appropriate box but that could be easily rubbed off and changed by an unscrupulous seller.

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 03:08:25 am
content: Brazil is 127V /220V 60Hz .

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 06, 2021, 03:25:19 am
content: Quote from: Jwillis on October 06, 2021, 03:08:25 amDon’t bank on that, some residential areas may still be 220V. Industrially, I send many a machine there rated for the quite bizarre 380V/60Hz configuration. That Volts per Hertz ratio was a royal PIA.

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 12:36:11 pm
content: Quote from: WattsThat on October 06, 2021, 03:25:19 amQuote from: WattsThat on October 06, 2021, 02:56:40 amThe label says the equipment is 120V. My mains here is 127V.Quote from: andy3055 on October 06, 2021, 02:45:49 amC1 is also out of circuit. I forgot to mention. Lifted one of it's legs. I though that with secondaries open the primary would not draw any current. But thinking about it, the transformer would need some current in order to generate the voltage in the secondaries even with them open. So, yes, might be a thing. I'll look and see if I can find a higher amperage fuse.Quote from: Jwillis on October 06, 2021, 02:51:06 amI've seen it before. People also call it "dim bulb tester" sometimes. I haven't thought of that. I guess I do have a socket laying around, I'll have to find a bulb. I'll definitely try that.I'll also dig a little deeper and try and identify U7, U2 and U6 (the regulators) to see some specifications. Feeding 12V to generate 5V might be a bit too much.About the main output, I don't think it's going to be less than 15V (the rated output). If the power supply had a step up function, there would probably be a coil somewhere, right? I can't see any.

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 02:00:38 pm
content: I was just going by what you said you had available for transformers. If the transformer is no good and if your up to it you could rewind it .

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 02:14:00 pm
content: Quote from: Jwillis on October 06, 2021, 02:00:38 pmI did thought of that but guessed it would be too crazy to try it. But you mentioning it makes me think is not such a crazy idea hahaEDIT:I'm still going to test it with the bulb, though. Just to be sure.

author: cbutlera
author_rank: Regular Contributor
timestamp: October 06, 2021, 02:19:17 pm
content: Quote from: augustol on October 06, 2021, 02:15:43 amDid you specifically check the power switch for shorting as Jwillis suggested? In my experience, that is more likely to fail than the transformer itself. You will have to disconnect the primary from the switch to do that.

author: WattsThat
author_rank: Frequent Contributor
timestamp: October 06, 2021, 02:59:52 pm
content: If the switch opens the load, it’s not bad. Those switches do physically break/fail but they're not likely to short, the isolation between poles is quite good. Typically, the push shafts just break off leaving either open or closed. Usually open due to the spring.

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 03:01:00 pm
content: Quote from: cbutlera on October 06, 2021, 02:19:17 pmI didn't, but now I did. No shorts on the main switch.Here in Brazil the mains voltage is not the same for the whole country. Some places are mainly 220V and some mainly 110V. It depends mostly on the company that makes the distribution and it changes from state to state. So, we also have to consider the possibility of someone getting the 110V power supply and plugging it to 220V. It happens.

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 03:09:46 pm
content: Quote from: augustol on October 06, 2021, 03:01:00 pmPossible and they just kept increasing the fuse value until it burned up .

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 03:18:21 pm
content: Quote from: Jwillis on October 06, 2021, 03:09:46 pmI hope it's not the case, though. I imagine someone that bought/used this supply before was either a student or a technician. So, at least the basic knowledge I expect from previous users.Fun fact: it has an inventory number and the sticker says "PROPERTY OF NOKIA Nokia Brasil Tecnologia DO NOT REMOVE" and some bar code. So I guess it once was used in an actual electronics lab.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 06, 2021, 04:07:32 pm
content: What's the part number on the transformer? Just to be 100% sure you have the right line voltage for your unit.9100-5250 is for 100V9100-5249 is for 115V9100-5252 is for 230V

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 04:50:57 pm
content: Quote from: TERRA Operative on October 06, 2021, 04:07:32 pm9100-5249.It's the 115V one.Now it got me thinking one thing. Although everyone here says the mains voltage is 110V, my cheap non-rms multimeter measures 127V. This extra 12V might be causing this issue?

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 08:13:41 pm
content: So I made a quick bulb tester here. Got a 70W bulb. It tuned on and stood brightly lit. Definitely shorted, right?

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 11:09:58 pm
content: I would say it is . If the primary is fine with no load on the secondary , the light should not light until a load is connected to the secondary. Or a secondary is shorted and overloading the primary . In either case the transformer is broken and needs rewinding.

author: Jwillis
author_rank: Super Contributor
timestamp: October 06, 2021, 11:16:56 pm
content: Quote from: augustol on October 06, 2021, 04:50:57 pmNo. The nominal voltage here is 120V but can reach 125V . Many appliances are rated for 117V and even 110V . So a few volts higher won't hurt a transformer . They will run warmer than optimal but won't burn up . Doubling the voltage or high voltage spikes (lightning) would burn a transformer.

author: augustol
author_rank: Contributor
timestamp: October 06, 2021, 11:28:02 pm
content: Quote from: Jwillis on October 06, 2021, 11:09:58 pmDo you have any info on how to make it? I've never done it and never seen anything related. I just know it's possible.I would like to make some further testing on the unit first to check if everything is ok, try and power it from an external source and stuff. but I would like to research a bit on how to do it and how does rewinding it works.

author: andy3055
author_rank: Super Contributor
timestamp: October 06, 2021, 11:40:29 pm
content: The secondaries are other top and will be thicker wire. Make note of the ends and unwind them. Then take a look at the top end of the primary. If the damage is closer to that end, you might just be able to repair it. Then re wind the secondaries as they were. It is not that hard as long as it is not a potted unit.

author: Jwillis
author_rank: Super Contributor
timestamp: October 07, 2021, 12:48:37 am
content: To do a full rewind can be expensive . Sometimes it's cheaper to get a rewinding shop to do it . Or if you can find another unit for parts . If you want to do a repair as Andy3055 suggests you'll still need to take apart the core . These cores are called laminated EI cores because each layer consists of over lapping E plates and I plates around a plastic bobbin .You can wind by hand but it takes longer and patients . Just remember how many times the wire goes around the bobbin. That is the winding count which is very important .Here's video of the general technique .

author: augustol
author_rank: Contributor
timestamp: October 07, 2021, 01:31:49 am
content: Quote from: Jwillis on October 07, 2021, 12:48:37 amOh my, that's a lot of work!

author: andy3055
author_rank: Super Contributor
timestamp: October 07, 2021, 03:59:29 am
content: Can you post a picture of your transformer?It is difficult, of course! But at least, like I said, you can see if it is just shorted close to the "top end" of the primary winding and fix it. Winding back the secondary windings are not that hard if you keep a count of the number of turns in each segment. You may be able to use the same wire also if you are careful. Use some cotton gloves to keep the oil from your hands away. Once it is done (if you decide to do so) put the thing in a metal container with a high wattage bulb to "bake" it. Good if you can re-varnish it. You may not find the varnish though in your area. Something like this:https://www.ebay.com/itm/331529483474?epid=9011367709&hash=item4d30b274d2:g:DOMAAOSwqu9VLBIlLike mentioned by JW above, the easier thing to do is to find another transformer that will have the same outputs (very unlikely though) or look for a guy who does this for a living. It should not cost that much.

author: augustol
author_rank: Contributor
timestamp: October 07, 2021, 06:24:21 pm
content: Quote from: andy3055 on October 07, 2021, 03:59:29 amThis weekend I will remove it from the board and post some pictures here. For now, I'm assessing costs for rewinding. I found some companies that rewind transformer, but by the looks of it, they only work with huge power transformers. I sent those companies an email, let's see if one of them will do it.I'm actually up to rewinding it myself but if I have to redo all the windings might be cheaper to get two or three transformers to replace this one. And I would probably have to put the outside of the power supply, it will be very ugly, but functional. Since covid the prices of copper wire skyrocketed here, let's see how this goes. But if I'm able to reuse most of the wire, it might be a good choice.

author: andy3055
author_rank: Super Contributor
timestamp: October 07, 2021, 09:25:20 pm
content: Big companies will not do this. Too much trouble for them. Find a small motor winding place. If you have to wind the primary, it is a lot of work as the wire will be too small to handle.

author: pqass
author_rank: Super Contributor
timestamp: October 07, 2021, 11:08:34 pm
content: I think you can replace the custom factory transformer with a standard 24VAC center-tapped toroidal tansformer plus adding two more secondary windings (~9VAC, ~30VAC CT).https://www.digikey.ca/en/products/detail/hammond-manufacturing/1182M12/4809336The service manual says that TP2-to-TP4 (the transformer's main secondary) is 25VAC +/- 10% (note 6 on page A-9)The 9VAC custom winding supports +5VDC for the front panel which is a pair of standard 7107 ADCs + 7-seg displays.The 30VAC winding is center-tapped to support up to +/-12VDC rails for the opamps etc.Both are regulated with 78XX/79XX series regulators; up to 1A but likely much less is used.The E3610A has an input power rating of 70W. So I found the above 80VA transformer that has 89mm diameter and 38mm height. I own a E3611A and the distance from the top of the heatsink where the factory transformer sits to just under the case is about 45mm. Just find a 1mm thick aluminum plate to rest on the old transformer bolt holes and mount the toroidal transformer on top of that.You probably could also get away with the 1182L12 at 50VA (giving 24V@2A or 12V@4A) but it's only marginally cheaper. I think this is a simple and elegant solution fitting for a premium power supply.

author: augustol
author_rank: Contributor
timestamp: October 08, 2021, 12:57:49 am
content: Quote from: pqass on October 07, 2021, 11:08:34 pmNote:I just found a supplier that can make custom transformers in low quantity. I'm excited! I think this will work!Now, I'm still confused about something: note 6 on page A-9 says the voltage between TP2 and TP4 is 25V +/-10% in low current range. Will this be different in high current mode?Plus, it does look a lot like a center tapped transformer, am I being dumb assuming this is a 50V center tapped? But the drawing the center tap is bit out of center. Is it possible they are different voltages or am I just being paranoid? Or they are completely different windings?EDITSorry for the tons of silly basic questions. I'm learning and transformers are not something I've dig in deeper yet. Also, thanks to everyone, I'm learning a lot here. <3

author: pqass
author_rank: Super Contributor
timestamp: October 08, 2021, 01:43:03 am
content: Quote from: augustol on October 08, 2021, 12:57:49 amThe note is basically telling you the max. winding voltage of the secondary but, come to think about it, I assumed that the center-tapped point is at half that; 12VAC. I may be wrong. Why don't you measure the resistance of each half of the seconary to confirm that it is, in fact, at the half-way point. It could be a 14VAC/10VAC or other odd split.In high-current mode, S2A switch only takes current from half (?) the secondary so that means it must sustain the full rated output of the power supply of 3A. So, I misspoke about using the 50VA (1182L12) transformer as its rating requires both secondaries to be in parallel to sustain 4A (however, 1182M12 can sustain 3.3A on just one half).QuoteIt may look a bit off but I wouldn't trust the visual. If each half is different it should say so somewhere.In the absence of that, I'd confirm by actually checking both winding resistances.It's NOT a 50VAC CT (or 25VAC-0-25VAC) for sure!The reason that it's using half the secondary to produce a max. 8V output is so that it only has to burn 4VAC vs. 12VAC+4VAC to get 8VDC out (@3A; 12W vs 48W in the output transistors).FYI: I measure 51VDC between TP2 and TP4 on my E3611A which makes sense since my supply can go to 40VDC output. And is consistent with note 6: "E3611A 47V +/- 10%"

author: pqass
author_rank: Super Contributor
timestamp: October 08, 2021, 03:54:41 pm
content: So I had a poke in my E3611A and measured the pins directly off of the transformer. This is what I see between the following pins (the square pad is pin 1, values shown are RMS):pin 1 - 2: 8VACpin 3 - 4: 15VACpin 4 - 5: 15VACpin 3 - 5: 30VACpin 6 - 7: 38VACpin 6 - 8: 25VACpin 7 - 8: 12VACAlthough I have a E3611A vs your E3610A we share the same design and only differ in a subset of component values.pin 1 - 2 is the winding for the front-panel.pin 3 - 4 - 5 is the center-tapped winding for the opamps (pin 4 is the center).pin 6 - 8 - 7 is the center-tapped main winding being controlled to the output posts (pin 8 is the "center"). But pin 8 is NOT a typical center where half the voltage is above and half below This one is 25VAC below and 12VAC above; 2/3rd to 1/3rd ratio. This makes sense since my PS output range is 20VDC and 35VDC. Your PS's range is 8VDC and 15VDC which is closer to 50/50. So I would expect your transformer be wound differently than mine for this winding. Also, I found anERROR IN THE SCHEMATIC; pins 7 and 8 of the transformer are swapped! I've confirmed it by following the trace on the board.

author: augustol
author_rank: Contributor
timestamp: October 08, 2021, 09:05:16 pm
content: Quote from: pqass on October 08, 2021, 03:54:41 pmHave you noticed that the note 6 on page A-9 might also be incorrect? You measured a total 38V on your E3611A, right? The note says it should be 47V. It caught my attention because because I was looking at the schematic and remembering the thing you said about the 1/3 2/3 ration between them. I also remembered that the low current should be 25V in my unit according to the notes. If I apply 25V as a 2/3 ratio, the total voltage should be 38V.I actually didn't remember your measurements so I came back here to check it because I though it was way to high supplying 38V to output 15V max. Also, the other taps give more voltage to the regulator but not that much. 8~9V become 5V, 15V becomes +/-12V. Getting 38V to supply 15V sounded odd to me.I'll later check if pins 7 and 8 are also swapped in my unit. But I guess they'll be.

author: augustol
author_rank: Contributor
timestamp: October 08, 2021, 10:59:08 pm
content: Quote from: andy3055 on October 07, 2021, 03:59:29 amHere are the pictures:

author: augustol
author_rank: Contributor
timestamp: October 08, 2021, 11:11:45 pm
content: Ok, so... Updates:I removed the transformer and did some measurements in DC Ohms.Primary: 2.5 ohmsPins 1-2: 1.2 ohmsPins 3-5: 8.3 ohmsPins 6-8:0.8 ohmsA note here: my multimeter is not acurrate at all in low ohms (under 20, maybe 50). If I short the leads, for example I measure0.8 ohms.I guess is no the primary that's shorted after all. It's the main output.I measured for ohms between the plus and minus of the (removed) bridge rectifier in the main output, I got no reading in any range. I tried continuity and all I got was a charging cap. I guess it's a sign it's not shorted. I will investigate the board further, though.

author: pqass
author_rank: Super Contributor
timestamp: October 09, 2021, 12:32:51 am
content: Quote from: augustol on October 08, 2021, 09:05:16 pmTrap for young players there... Notice note 6 says between TP2 and TP4. Well those points are AFTER the bridge and the main bulk cap C2, and are in DC! Since I didn't have a load attached at the output posts on the front panel (and with range button on low - pushed in) then the voltage at the test points will basically be the peak of the wave. I measured 38VAC (this is RMS) on the transformer pins 6-7, therefore the peak is 38*sqrt(2)=53VDC less 2 diode drops is 51VDC. This is within 10% of 47VDC as per note 6 so I have no reason to doubt the values for the other PS models.The reason note 6 says to put it in low mode is so that the S2A switch uses the full secondary and not (in my case) the 2/3rds position.In your case, the E3610A, the low position is your whole secondary of 25VDC and my expectation of your transformer to be a true 50/50 split, so your high position should pick the center, therefore, should output 12.5VDC.I'm NOT saying all transformers will be 2/3rds - 1/3rd split like mine. These are are all custom transformers for each model so I assume the split would be according to the ratio of the hi/low voltages on the front panel label.QuoteAlthough my E3611A is labeled 0-20V (range button out) or 0-35V (range button in) my voltage dial can go 0-33V or 0-40V, with no load attached. If the range button is on high (button out) the TP2-TP4 voltage sinks to 33VDC; this is used to guarantee 20VDC (not 15VDC as you said). With a load attached, in hi-mode I can sustain 26V@1.5A (any higher voltage I go into CC mode) and in low-mode 40V@0.84A; this over the rating!

author: pqass
author_rank: Super Contributor
timestamp: October 09, 2021, 01:15:27 am
content: Quote from: augustol on October 08, 2021, 11:11:45 pmYou'll have to lift one leg of C1 otherwise you'll just mess the readings.If you could measure all three; between 6-7, 7-8, and 6-8 using croc/aligator clips (so hand pressure is removed from the readings) that would allow us to determine the ratio in the main center-tapped winding. The actual low resistance value is not important; just that you did all three in the same manner.My expectation is that pin 8 is the center-tapped, pin 6 is one side, and pin 7 is the other side of the secondary. Based on your E3610A being labeled as 8V (hi-mode) or 15V (low-mode), a ratio of approx. 50/50, I expect a 50/50 in each half of the secondary. So, I predict 6-8 should have the same resistance as 7-8, and 6-7 is twice that.Let me know otherwise.

author: augustol
author_rank: Contributor
timestamp: October 09, 2021, 01:44:15 am
content: QuoteOh... haha Yeah, I should've taken that into consideration. I actually saw that when I was reading and identifying the points and etc, but I didn't really think through that. You are right.QuoteI did, actually. I was measuring the DC side. I was probably reading C2 which for now I do not intend to mess with. I did find a strange reading in CR3 though, the diode in the output which I supose is a reverse voltage protection. Not saying it's buned yet. I'll have to lift one of it's legs and measure again. Might just be because it's in circuit.QuoteOk, so I did the measurements again between all the taps with alligator clips, but not a big difference:Primary: 2.2R1-2: 1.2R3-4: 4.5R4-5: 4.4R3-5: 8.1R6-7: 0.8R7-8: 0.8R6-8: 0.8REDIT:Like you said, it makes sense that in the E3610A should have symmetrical taps on the output part. Which makes the second tap 12.x volts. Which makes sense for delivering 8V.

author: pqass
author_rank: Super Contributor
timestamp: October 09, 2021, 01:53:11 am
content: Quote from: pqass on October 09, 2021, 12:32:51 amCORRECTION: Note 6 says to expect 25VDC on TP2-TP4 (E3610A) and we assume the peak of the wave when output is unloaded. Therefore, using my earlier math backwards, what's the AC volts (RMS)? A: 25VDC/sqrt(2)=18VAC and the center-tapped is 9VAC (assumes 50/50 split; reasoning in my last message).

author: pqass
author_rank: Super Contributor
timestamp: October 09, 2021, 02:04:09 am
content: Quote from: augustol on October 09, 2021, 01:44:15 amIf you removed the bridge, you should be measuring across the AC ("~") pads with C1 leg lifted and the range switch in low-mode (pushed-in). That way you'll get the full secondary winding.QuoteThose last three are a problem. 6-7 should be equal to the other two added together.Given my last message (thinking now you have a 18VAC CT secondary) I don't think your meter can actually measure such a small winding.

author: augustol
author_rank: Contributor
timestamp: October 09, 2021, 02:12:42 am
content: Quote from: pqass on October 09, 2021, 02:04:09 amI removed the transformer from the board. the AC side now is just a cap with one leg lifted. I was just making a quick test to see if I could find anything obvious on the board apart from the transformer.Yeah, my meter is a problem, actually. It was actually the first thing electrical I ever got. I do intend to get a better one in the future, but for now that's what I have available.But, the three taps measuring the same resistance could be a sign of a short, no? I don't know what to expect in terms of resistance from the primary (in case it is the shorted one).

author: pqass
author_rank: Super Contributor
timestamp: October 09, 2021, 02:37:33 am
content: Quote from: augustol on October 09, 2021, 02:12:42 amIf you have a "relative" mode on your meter you can null-out the meter leads and try measuring all three pins again.I'd expect each half to be of similar resistance to pins 1-2 (8VAC) but probably a little lower given the 6-8-7 secondary has thicker wire.But, yeah, it may be shorted too.BTW: I measure 4.7 ohms across the leads of the main power switch (S3) directly in front of my  transformer.Yours should be the same if you're in 120VAC service area.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 09, 2021, 04:00:01 pm
content: Here you go, because I crave acceptance and praise from random people on the internet, I measured the output side of the transformer in my 100V E3610A with my freshly calibrated HP 34461A multimeter in 4-wire mode.The transformer was removed from the unit for the test.(Values in brackets are my best guess at nominal values)1-2: 0.357 Ω (0.36 Ω)3-4: 3.798 Ω (3.8 Ω)3-5: 7.563 Ω (7.6 Ω)4-5: 3.762 Ω (3.8 Ω)6-7: 0.202 Ω (0.2 Ω)6-8: 0.111 Ω (0.1 Ω)7-8: 0.092 Ω (0.1 Ω)

author: augustol
author_rank: Contributor
timestamp: October 09, 2021, 05:02:33 pm
content: Quote from: TERRA Operative on October 09, 2021, 04:00:01 pmOh my, thank you very much. You didn't need to do that. That's very helpful.But yeah, my multimeter can't read resistances that low. For some time I've been considering that 0.8R as an "offset" and it kind of worked for some cases. For example, comparing my measures and yours between 1-2, there is approximately 0.8R difference.But 0.1 and 0.2 my multimeter definitely won't be able to measure. Not even considering this "offset".Anyways, I'm waiting for a reply from the guy that makes custom transformers. I've messaged him today in the morning. I guess monday I'll get a reply.

author: pqass
author_rank: Super Contributor
timestamp: October 09, 2021, 05:35:09 pm
content: Quote from: TERRA Operative on October 09, 2021, 04:00:01 pmTERRA,if you could measure the AC RMS voltages between those pins, then that would finally put to rest this discussion on the secondary center tap voltage.Thanks.

author: TERRA Operative
author_rank: Super Contributor
timestamp: October 10, 2021, 12:32:54 am
content: Alrighty, here are the E3610A transformer output voltages.Open circuit voltages:1-2: 7.9V3-4: 14.6V3-5: 29.2V4-5: 14.6V6-7: 20.4V6-8: 13.1V7-8: 7.3VTransformer installed with no load on output terminals and all dials set to 0.1-2: 7.9V3-4: 14.4V3-5: 28.8V4-5: 14.4V6-7: 20.3V6-8: 13.0V7-8: 7.3V

author: pqass
author_rank: Super Contributor
timestamp: October 10, 2021, 02:14:33 am
content: Quote from: TERRA Operative on October 10, 2021, 12:32:54 amThanks TERRA.Well, that settles it, that last winding has a similar 2/3rds-1/3rd split just like my E3611A.augustol,if rewinding doesn't work out, I still think you can opt for the 24VAC CT 80VA toroidal transformerhttps://www.digikey.ca/en/products/detail/hammond-manufacturing/1182M12/4809336and add these additional secondary windings 8VAC, 30VAC CT, and a 4VAC. Assuming 0.25V/turn***, that would mean 32 turns, 60 turns (of a pair), and 16 turns, respectively. The first two can be 24AWG but the last one should be at least 22AWG (5A capable).Why the additional 4VAC? A:The full 24VAC may produce too much heat in the pass transistors so by connecting a 4VAC winding "backward" to the direction of the end lead, we can subtract those 4 extra volts. This will get you to a 0VAC-12.5VAC-20VAC secondary as confirmed by TERRA.It's not cheap though; CA$80. But it's easier to wind secondaries than primaries.***You need to confirm this with the actual transformer you buy.