Re: Should I power this thing up?(I HAVE NO VARIAC)
Sorry Techgeek , i had some clients . Well , you treat a rectifier just like it is 4 diodes bridged together , the first one goes from ~ sign to the minus sign , the second goes from ~sign to the positive sign , the third goes from the plus sign to the negative sign and the fourth goes from the plus sign to the negative sign ...
Should I power this thing up?(I HAVE NO VARIAC)
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Diodes are a single PN junction. They conduct in one direction only. On semiconductors the arrow always points at negative. Therefore put the negative lead on the band of the diode and it should conduct. It will still show resistance because it's a "semi" conductor. That's why a diode mode is nice. It shows the voltage drop. One way is infinite the other is around a half a volt. A rectifier is merely a diode bridge. It kinda makes a rough DC out of AC. So, figure out which leg is positive and negative and check it. Best done out of circuit. If you can find the paperwork on the rectifier it will show you how it's setup. I would suspect your unit is somewhere from 1976 to 1980 manufacture date. Before then they usually had four simple diodes for a rectifier after that they went to black plastic faces.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Check on youtube on how to test a bridge diode easier to do that writing and possibly causing confusion, basically a rectifier has 4 diodes in side of it, normally the pins are labelled on it where the diodes are.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
mine can go all the way up to 2000k. So plug it in and give it a go?Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Ahh right ok, its a little harder with resistance mode as it wont be able to find a voltage drop just resistance across the part/circuit. Maybe pick a cheap DMM up ? You can get them off ebay for £3 with probes with diode test. Still with resistance as its high as you said, chances of it being shorted is nothing.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
uhhh... I don't have a diode checker on my DMM, only resistance, VAC, VDC, and that's about it. Need a photo?Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Use diode mode on your meter.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Note that some diodes could give erroneous measures on board if it's relayed with some resistance . In such case , you have to remove one leg of the diode .Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
How do I check transistors for shorts and/or rectifiers? The output diodes on the PSU are far from shorted, one reads almost 200K resistance.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Since no silicons are shorted , fuses are okay , then why not ..Capacitors , if dried , will show different symptoms , but not much more than the fuse can handle .
Those Fisher were something , Akai are better , and the twos were formidable if equipped with JBL's , the good old days .Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
That's a big myth. A Variac doesn't limit current. How would it? It's nothing but a variable autoformer- a dead short on its output will pull excess current even with the knob way down.
IOW, even with a Variac, you still use a "dim bulb." Try a 40W lamp in series with the line, and verify all power supply voltages begin to come up. Then a 60W, 75. The amp should be working at this point- check across emitter resistors for excessive voltage= means amp bias "ran away." Fix this before larger lamp or full line voltage.
DC offset should be below 250mV at the point amp comes up on reduced voltage. Some had more offset at reduced voltage- long tailed pair isn't quite symmetrical at this point. If offset minimal, a larger lamp/higher voltage should make DC offset decrease.
If there are offset and bias pots, clean them! A bad bias pot can take the output/driver transistors out, as well as other components. A set of four Motorola/Onsemi 2119x is about $20.
Last edited by kaboom; 07-31-2016, 11:30 PM.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
This Fisher is made by Sanyo when they bought out Fisher name, so basically a Sanyo with Fisher name on it.
You can use 60 Watt lamp for now, or use two 60W in PARALLEL to give 120 W.
Last edited by budm; 07-31-2016, 11:09 PM.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Sorry to tell you this. Fisher was sold by the original owner. Anything that says "Studio Standard" was made after the sale and is not considered to be valuable at all. I have a system I bought in 1984. It just isn't as good as one of the big three, Pioneer, Sansui, or Marantz. It's worth saving. It just won't ever be as valuable as one of the other three. People are discovering what real music can sound like and ditching their digital equipment. That's why you see prices rising on all the old stuff. In the 80's and 90's you couldn't give it away. Now, it's in high demand.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
Sorry to tell you this. Fisher was sold by the original owner. Anything that says "Studio Standard" was made after the sale and is not considered to be valuable at all. I have a system I bought in 1984. It just isn't as good as one of the big three, Pioneer, Sansui, or Marantz. It's worth saving. It just won't ever be as valuable as one of the other three. People are discovering what real music can sound like and ditching their digital equipment. That's why you see prices rising on all the old stuff. In the 80's and 90's you couldn't give it away. Now, it's in high demand.Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
I didn't find any active listings for that particular model (though I did see some similar ones), but a search of completed listings (these go back 90 days) found 3 one for $51, one for $135 and one for $175, the two more expensive ones were tested and cleaned (though it doesn't appear any internal work was done on these, one that has been recapped/re-lamped may be worth more, but maybe not hard to say) and from established sellers (while the $51 one was from a 0 feed back seller with a limited description).Leave a comment:
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Re: Should I power this thing up?(I HAVE NO VARIAC)
While I generally don't have any complaints with Marantz (but also realize other makes have receivers that are as good or better), the prices have gotten absolutely ridiculous. I have a model 2015 receiver I bought about 10 years ago for around $35 in excellent condition (only needed one bulb replaced), today those are going for around $100-250 for a little 15 WPC receiver with 4 inputs (2 tape, phono, Aux). When I bought the 2015, 2270/2275s were going for $200-300 fully working and in excellent cosmetic condition and $400-500 fully refurbished with new caps and lamps and calibrated, which I thought was pretty reasonable (not "cheap", but ok for a receiver with those capabilities and build quality), today you are looking at double that or more (and a lot more if you want a wood case), there are just too many good alternatives out there for far more reasonable prices to justify that.Last edited by dmill89; 07-31-2016, 09:47 PM.Leave a comment:
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by momakaI know I've been a little scarce lately (like the last 2-3 years), but I'm still here and still doing my thing with fixing PSUs.
For today's considerations, I have a Seasonic B12 BC-550 [A551bcafh] 550 Watt ATX power supply for you (click on links for full size images).
https://www.badcaps.net/filedata/fetch?id=3591771
https://www.badcaps.net/filedata/fetch?id=3591772
It's a modern ATX unit with fixed (non-modular) cables and an 80-plus bronze certificate. Here's the label:
https://www.badcaps.net/filedata/fetch?id=359177... -
by tony359Hi all,
I have an old Apple II monitor to restore and I do have a big variac. I've always wondered whether a variac is a good idea to power on equipment which has been unpowered for (likely) decades?
When it comes to analogue stuff, I suppose it's ok and I'm probably going to see the device slowly coming back to life with a lower voltage applied.
But I suppose this won't work for devices with digital components in it as they won't work unless the proper voltages are applied?
In case of an old monitor, it is safe/good for the monitor to...10-13-2023, 02:47 AM -
by angelosHello everyone,
I was wondering if anyone in the forum can tell me how they use the variac transformer to check a switch mode power supply that they had just repaired.
I wanted to know how they adjust the votlage, do they start from zero and turn it up slowly or rather switch on that about 60V ac ( My country we use 220V ac) and hope for the best.
Also what sounds the PSU should make, what sounds wrong etc. Also if i have a scope what can i check for.
The reason why i am asking is i have a Sony LED TV PSU whose PFC circuit shorted out and upon closer inspection a... -
by CapSnap123I have an old "Adjust-a-Volt" variac. Shortly after I bought it, it started smoking and now the windings look burned for about 2 inches around the left side. Is it possible to fix this or bypass the shorted windings? I'm not sure how to detect where the bad windings are, except by appearance.
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by evilkittyMy Mom bought some cheap motion sensor lights on wish... then complains about about batteries and this thing chews though them, well it uses 4 AAA batteries and a pack of rechargeable ones is about 13 USD
well since it uses 4 AAA and rechargeable are 1.2v and non-recharge at 1.5 this thing must work with 4.8-6v, I'll shove a USB cable on it, infant i will use a broken phone charge cable... dam this thing uses 430 mA and they made it battery powered...
lets ignore the fact that i thought the board fit both ways... and the wire color is reversed going to the board...-
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