Follow It Home Posted March 31, 2008 Share Posted March 31, 2008 Hey everyone, my trio mod is here and before I sit down and seriously work on it I would just like someone to run through important pre-work checks for me. Like how to check the voltage and things like that, just so I dont kill myself :-P. I'm pretty confident on taking the chassis out, but are there some thing I should know about it? Thanks everyone. Link to comment Share on other sites More sharing options...
TWANG Posted March 31, 2008 Share Posted March 31, 2008 by memory alone.. I shall decieve ye! but here goes. black probe to ground on chassis. I use alligator clip to common star ground nut. red probe to R10 both sides, R12 both sides, R3 both sides. oh. amp turned on, speaker plugged in, volume down and warmed up for ten minutes. nothing plugged into the input jack. Pin 1 3 5 7? maybe 9, too. on the 12ax7 pin 3 5 7 8 or 9? on the el84 DCmv all. get those numbers and I'll see if I can pull my papers out for accurate ranges and then tell you what they all are. I can never remember it when I'm not inside. TWANG Link to comment Share on other sites More sharing options...
Follow It Home Posted March 31, 2008 Author Share Posted March 31, 2008 ...Ill be honest with you tang, once you got to the part about turning it on and stuff, I got lost. I was just talking about checking the voltage to make sure its not dangerous for me to work on, is that the first part? I just need to know how to check the dangerous voltages, but I would still like to know what you were talking about after, haha. Link to comment Share on other sites More sharing options...
bluefoxicy Posted March 31, 2008 Share Posted March 31, 2008 Yo home boy. Little tip for when you're putting it in. When you solder in the trio you're going to want to solder to R6 and R8 on the board, as well as to the two right pins (from the front) on the vol pot. You CAN bend the leads of the wire into hooks and loop under R6 and R8's ends. Don't. I did it, it's dumb, I had to UNDO it to fix a mistake. Just do it like it says to do on Vol (detailed below). What you do is use a very little solder to tin the ends of R6 and R8 (put a tiny drop there, but solder nothing to them). Use however much solder you want on the ends of the wires, and then melt excess off with the iron, it'll drip and leave a silver-coated wire end. Then, bring the wire to the solder point. Hit it with the iron. The solder on both the resistor lead and the wire will melt and join; let it cool (blow on it gently), then let go, move on to another. Give it a few minutes to cool down when you're done (way excessive), give the wires a tug, they should hold. IF you make a mistake, hit it with the iron and tug. It'll melt the joint and slip right out. No need to re-tin. Link to comment Share on other sites More sharing options...
Follow It Home Posted March 31, 2008 Author Share Posted March 31, 2008 Thanks blue. But still anyone want to help me with how to check the voltage of the amp? Im sure all of you do it before you work on it, I just need an explanation on how to do it. Thanks. Link to comment Share on other sites More sharing options...
strangedogs Posted March 31, 2008 Share Posted March 31, 2008 I'm a Maintenance Supervisor (last 22 years) - I've taken 110 and 220 loads of times - it'll make you tough Link to comment Share on other sites More sharing options...
bluefoxicy Posted March 31, 2008 Share Posted March 31, 2008 I have no advice on that. I tend to dive in right after turning the amp off and unplugging it; I have no concept of mortality and you may want to ignore any safety advice you get from me Link to comment Share on other sites More sharing options...
Follow It Home Posted March 31, 2008 Author Share Posted March 31, 2008 Well can I just trust the bleeder caps or whatever they installed on V. 3 that i have heard about? Or dont those exist, haha. Link to comment Share on other sites More sharing options...
layboomo Posted March 31, 2008 Share Posted March 31, 2008 Well...first of all any voltage that goes across your chest can stop your heart and it's the amperage that kills you not the voltage! It's a bleed resistor thats built in to the amp to discharge the caps and after your amp is off and unplugged for 15 minutes or so it should be safe to work on. You can also plug your guitar in and with the volume up strum your guitar while you unplug the power cord and you'll hear the caps drain as it powers down. When you slide the chassis out you can clip the black lead from a meter to the chassis ground and check the filter caps for any voltage if you want to be absolutely sure. Be safe! Dead is dead! I'm not trying to scare you but have a healthy respect for electricity......it's really not a joke. Link to comment Share on other sites More sharing options...
Follow It Home Posted March 31, 2008 Author Share Posted March 31, 2008 Thanks Layboomo, where do I put the other probe to check the caps? Thats all I need to know and I think I should be good. Link to comment Share on other sites More sharing options...
TWANG Posted April 1, 2008 Share Posted April 1, 2008 oh caps discharge.. sorry. *L* "the black lead from a meter to the chassis ground and check the filter caps for any voltage if you want to be absolutely sure." you'd put the red probe to the caps leads. 'check the filter caps' he just forgot to say with the other probe. I thought you were talking about the problems vjs have with high voltages like at the heaters of the tubes, etc.. and how to check them for bias, etc.. TWANG Link to comment Share on other sites More sharing options...
Follow It Home Posted April 1, 2008 Author Share Posted April 1, 2008 Are the filter caps the big black caps on the board? Link to comment Share on other sites More sharing options...
TWANG Posted April 1, 2008 Share Posted April 1, 2008 C6 and C9 right next to each other on the end.. tall black caps. 100uF is better. Link to comment Share on other sites More sharing options...
Follow It Home Posted April 1, 2008 Author Share Posted April 1, 2008 Thanks Twang, but what is UF? haha sorry if my ignorance is frustrating. Link to comment Share on other sites More sharing options...
tunghaichuan Posted April 1, 2008 Share Posted April 1, 2008 Thanks Twang' date=' but what is UF? haha sorry if my ignorance is frustrating.[/quote'] Stands for "micro Farad" the symbol is µF, but the "u" on the keyboard is easier to type. tung Link to comment Share on other sites More sharing options...
TWANG Posted April 1, 2008 Share Posted April 1, 2008 they measure capacitance in farads and volts. like.. .022uF, 600V. wait till you start having to figure out nF and pF and so forth. luckily there are charts on the web. though I still wound up with a lot of the wrong caps! Link to comment Share on other sites More sharing options...
Eracer_Team Posted April 1, 2008 Share Posted April 1, 2008 This is one ugly thread, meaning the answers to your initial question are all over the place... Yes version 3 VJ's have a bleeder resistor (not a cap), it will as long as its good will drain the power supply cap's within seconds. BUT you should still measure to be sure... 350VDC at 5amp's will kill you. :-) ( also we've all taken zapps from 120vdc/220 don't try sticking a fork into the wall outlet to see if you'll survive.. bad idea, I see strangedogs added a wink in there but it doesn't come across the way i think it was intended). print out the schematic for the version of VJ you have, this keeps track of your voltage when you write them down for reference. looking at the schematic and the amp out of the cabinet, you'll notice the black cans (those are the capacitors) but since their legs are on the underside of the board you can't access them easy) So to check that the bleeder resistor has done its job... clip the black lead of your meter to the nut that has all the green wired grounds going to it. then with the meter in vdc take the red probe and measure either side of R10, R12, R13... normal operating voltage is more than 200~357vdc.. so you should only measure a few milli-volts when powered off. The voltage readings that Twang was referring to is measuring the live operating voltages, which you'll need to do when you start to adjust the bias voltage (the power that runs the tubes) to not kill your tubes. same procedures apply for checking the cap voltages as does live running voltages. Clip the black lead of your meter to the ground screw nut and use the red lead to probe the locations Twang mentions... remember to plug in your speaker or you’ll have a lot more to fix, like a blown output transformer, etc. Don't use your finger in the live running amp as temperature gauges or voltage probes... its not advisable. Hope this helps Link to comment Share on other sites More sharing options...
strangedogs Posted April 1, 2008 Share Posted April 1, 2008 awww - c'mon COWBOY UP girls... and I was kiddin' - it ain't the volts IT'S THE AMPS. I had an old A/C cap (45 mfd @470v) in the back of my truck and actually had the bejeebies knocked outta me one day when I grabbed it... wheeeeeee! Link to comment Share on other sites More sharing options...
bluefoxicy Posted April 1, 2008 Share Posted April 1, 2008 IT'S THE AMPS Not even, it's the milliamps! 10mA, to be precise, directly across the heart will definitely kill you. They made us explain PNP and NPN transistors and electricity and stuff when we were getting our radio operators' licenses back in... um. What year was it when I was 11? 97 or something? I never got higher than Tech+ but... Good information though. Something everyone should know: electricity will kill you. Link to comment Share on other sites More sharing options...
tortuga Posted April 1, 2008 Share Posted April 1, 2008 looking at the schematic and the amp out of the cabinet, you'll notice the black cans (those are the capacitors) but since their legs are on the underside of the board you can't access them easy) So to check that the bleeder resistor has done its job... clip the black lead of your meter to the nut that has all the green wired grounds going to it. then with the meter in vdc take the red probe and measure either side of R10, R12, R13... normal operating voltage is more than 200~357vdc.. so you should only measure a few milli-volts when powered off. If you were wanting to discharge the caps as a precaution (assuming the bleed resistor didn't work) is either side of R10, R12, and R13 the points that you would need to connect to ground to discharge the cap? Link to comment Share on other sites More sharing options...
Eracer_Team Posted April 1, 2008 Share Posted April 1, 2008 yes. if the bleed resistor didn't do its job, you would have to make a discharge tool (some call it a shunt) to bleed the voltage to ground... (a wire, with a resistor and protective covering, probe tip and an aligator clip) You just can't attach a wire from the cap to ground or you'll start your own arc welding school. Link to comment Share on other sites More sharing options...
tortuga Posted April 1, 2008 Share Posted April 1, 2008 Sorry...I did a poor job of asking the question. I understand I would need to use a "shunt" with a resistor inline, but my question is would shorting from ground to the resistor points you describe above be the suggested way to short the capacitor? Or should you connect to the capacitor itself? Link to comment Share on other sites More sharing options...
layboomo Posted April 1, 2008 Share Posted April 1, 2008 The cap's are soldered to the botom of the PCB..so the resistors are the only top side places you can get to easily on the stock board. Link to comment Share on other sites More sharing options...
Eracer_Team Posted April 1, 2008 Share Posted April 1, 2008 Thanks Lay... the cap's are soldered to the bottom side of the board (although they stickup on the top side) so the resistors as LayB point out are the only things on the top side you can gain access to. Since one side of the cap is connected to ground, by touching your discharge tool to the resistor points you mentioned would short the cap's to ground (well not really short them since you power shunt has a resistor in it). I wouldn't worry too much on discharging of the cap's manually too much... Just measure the voltage on them via the resistors R10/12/13 the cap's are in parallel so they should all discharge equally. Only if the R11 drain resistor doesn't do its job then go for the manual discharge tool Link to comment Share on other sites More sharing options...
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