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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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VOX AC30/6 TB
All valve, no solid state devices, probably made 2002 from barcode date? and
2001 date on Sovtek 5AR4. Powered on for about 5 seconds with cracks and bangs then HT light went out and dead. Inside looks and smells fine but "gently" blown HT fuse. I've not tested the valves yet. 1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and all 4 EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has crudely cut one of the 2 grounds to the pcb, presumably trying to reduce hum when it was working. All DVM DC resistance measurements of the transformers seem ok. Any pointers to known problems with this version? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#2
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VOX AC30/6 TB
"N Cook" wrote in message
... All valve, no solid state devices, probably made 2002 from barcode date? and 2001 date on Sovtek 5AR4. Powered on for about 5 seconds with cracks and bangs then HT light went out and dead. Inside looks and smells fine but "gently" blown HT fuse. I've not tested the valves yet. 1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and all 4 EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has crudely cut one of the 2 grounds to the pcb, presumably trying to reduce hum when it was working. All DVM DC resistance measurements of the transformers seem ok. Any pointers to known problems with this version? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ First question back to you is.. is the HT fuse after the rectifier or before it? Or, are you really talking about the AC mains fuse? If the fuse is really in the AC mains line, then almost all my bets are going to be on a shorted power transformer or a shorted MOV or line bypass capacitor. If the fuse is after the rectifier, then you should pull the rectifier tube, replace the fuse, and see if the fuse blows again. If it blows again, then check to see if maybe one side of the power line is shorted to ground... possibly caused by a shorted MOV or line bypass capacitor. Or a stray piece of wire, or other malady. If the fuse doesn't blow again, then you have a bit of troubleshooting to do. Most likely a shorted B+ filter capacitor or shorted tube. Be sure to keep your eyes peeled for stray wire clippings. Cheers!!!! -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer to the end, the faster it goes. |
#3
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VOX AC30/6 TB
DaveM wrote in message
. .. "N Cook" wrote in message ... All valve, no solid state devices, probably made 2002 from barcode date? and 2001 date on Sovtek 5AR4. Powered on for about 5 seconds with cracks and bangs then HT light went out and dead. Inside looks and smells fine but "gently" blown HT fuse. I've not tested the valves yet. 1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and all 4 EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has crudely cut one of the 2 grounds to the pcb, presumably trying to reduce hum when it was working. All DVM DC resistance measurements of the transformers seem ok. Any pointers to known problems with this version? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ First question back to you is.. is the HT fuse after the rectifier or before it? Or, are you really talking about the AC mains fuse? If the fuse is really in the AC mains line, then almost all my bets are going to be on a shorted power transformer or a shorted MOV or line bypass capacitor. If the fuse is after the rectifier, then you should pull the rectifier tube, replace the fuse, and see if the fuse blows again. If it blows again, then check to see if maybe one side of the power line is shorted to ground... possibly caused by a shorted MOV or line bypass capacitor. Or a stray piece of wire, or other malady. If the fuse doesn't blow again, then you have a bit of troubleshooting to do. Most likely a shorted B+ filter capacitor or shorted tube. Be sure to keep your eyes peeled for stray wire clippings. Cheers!!!! -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer to the end, the faster it goes. MOV= metal oxide varistor ? Probably the most diagnostic feature is the 500mA HT fuse, on the DC side of the rectifier tube, is a small gap in the fuse filament with a glob on one broken end, both remnants axially present in the barrel, no staining inside barrel at all. Last gasp rather than catastrophic failure. I'm struggling with sticky needle on my valve tester , again. I know if i poke around in the meter I will totally bugger up the movement , so no use rather than problematic use with a lot of case tapping. As an aside anyone know when barcodes started appearing on electronic kit or components? for age determination assistance. Mid 1980s is my recollection but googling has not helped -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#4
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VOX AC30/6 TB
N Cook wrote in message
... DaveM wrote in message . .. "N Cook" wrote in message ... All valve, no solid state devices, probably made 2002 from barcode date? and 2001 date on Sovtek 5AR4. Powered on for about 5 seconds with cracks and bangs then HT light went out and dead. Inside looks and smells fine but "gently" blown HT fuse. I've not tested the valves yet. 1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and all 4 EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has crudely cut one of the 2 grounds to the pcb, presumably trying to reduce hum when it was working. All DVM DC resistance measurements of the transformers seem ok. Any pointers to known problems with this version? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ First question back to you is.. is the HT fuse after the rectifier or before it? Or, are you really talking about the AC mains fuse? If the fuse is really in the AC mains line, then almost all my bets are going to be on a shorted power transformer or a shorted MOV or line bypass capacitor. If the fuse is after the rectifier, then you should pull the rectifier tube, replace the fuse, and see if the fuse blows again. If it blows again, then check to see if maybe one side of the power line is shorted to ground... possibly caused by a shorted MOV or line bypass capacitor. Or a stray piece of wire, or other malady. If the fuse doesn't blow again, then you have a bit of troubleshooting to do. Most likely a shorted B+ filter capacitor or shorted tube. Be sure to keep your eyes peeled for stray wire clippings. Cheers!!!! -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer to the end, the faster it goes. MOV= metal oxide varistor ? Probably the most diagnostic feature is the 500mA HT fuse, on the DC side of the rectifier tube, is a small gap in the fuse filament with a glob on one broken end, both remnants axially present in the barrel, no staining inside barrel at all. Last gasp rather than catastrophic failure. I'm struggling with sticky needle on my valve tester , again. I know if i poke around in the meter I will totally bugger up the movement , so no use rather than problematic use with a lot of case tapping. As an aside anyone know when barcodes started appearing on electronic kit or components? for age determination assistance. Mid 1980s is my recollection but googling has not helped -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ the third EL84 tested , started out normally then rapidly accelerated off the scale. I've never had the protection relay on my Avo CT 160 dropping out before. I had to get inside to manually reset it and took the opportunity to sort out the meter needle sticking problem, much easier to get to and into this meter movement than I'd thought. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#5
Posted to sci.electronics.repair
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VOX AC30/6 TB
"N Cook" wrote in message ... N Cook wrote in message ... DaveM wrote in message . .. "N Cook" wrote in message ... All valve, no solid state devices, probably made 2002 from barcode date? and 2001 date on Sovtek 5AR4. Powered on for about 5 seconds with cracks and bangs then HT light went out and dead. Inside looks and smells fine but "gently" blown HT fuse. I've not tested the valves yet. 1 of the 22K 1/3W HT R/C dropper resistors slightly discoloured and all 4 EL84 1/2W, 100 ohm grid resistors slightly discolured. Someone has crudely cut one of the 2 grounds to the pcb, presumably trying to reduce hum when it was working. All DVM DC resistance measurements of the transformers seem ok. Any pointers to known problems with this version? -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ First question back to you is.. is the HT fuse after the rectifier or before it? Or, are you really talking about the AC mains fuse? If the fuse is really in the AC mains line, then almost all my bets are going to be on a shorted power transformer or a shorted MOV or line bypass capacitor. If the fuse is after the rectifier, then you should pull the rectifier tube, replace the fuse, and see if the fuse blows again. If it blows again, then check to see if maybe one side of the power line is shorted to ground... possibly caused by a shorted MOV or line bypass capacitor. Or a stray piece of wire, or other malady. If the fuse doesn't blow again, then you have a bit of troubleshooting to do. Most likely a shorted B+ filter capacitor or shorted tube. Be sure to keep your eyes peeled for stray wire clippings. Cheers!!!! -- Dave M MasonDG44 at comcast dot net (Just substitute the appropriate characters in the address) Life is like a roll of toilet paper; the closer to the end, the faster it goes. MOV= metal oxide varistor ? Probably the most diagnostic feature is the 500mA HT fuse, on the DC side of the rectifier tube, is a small gap in the fuse filament with a glob on one broken end, both remnants axially present in the barrel, no staining inside barrel at all. Last gasp rather than catastrophic failure. I'm struggling with sticky needle on my valve tester , again. I know if i poke around in the meter I will totally bugger up the movement , so no use rather than problematic use with a lot of case tapping. As an aside anyone know when barcodes started appearing on electronic kit or components? for age determination assistance. Mid 1980s is my recollection but googling has not helped -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ the third EL84 tested , started out normally then rapidly accelerated off the scale. I've never had the protection relay on my Avo CT 160 dropping out before. I had to get inside to manually reset it and took the opportunity to sort out the meter needle sticking problem, much easier to get to and into this meter movement than I'd thought. The schematics for most of the AC30 derivatives are on the VOX website for free download Arfa |
#6
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VOX AC30/6 TB
Arfa Daily wrote in message
... The schematics for most of the AC30 derivatives are on the VOX website for free download Arfa only the older amps Laney did the same but pulled them from open access a few months ago. I'd managed to download about 2/3 of them, over a few months, before they were all pulled. Just for my personal use at some future date. I would suggest doing the same for any site that has such technical details. I assume some accountant or intelectual property rights lawyer comes along and says "remove that content" from open access that some well meaning technician had put up there. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ |
#7
Posted to sci.electronics.repair
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VOX AC30/6 TB
N Cook wrote in message
... Arfa Daily wrote in message ... The schematics for most of the AC30 derivatives are on the VOX website for free download Arfa only the older amps Laney did the same but pulled them from open access a few months ago. I'd managed to download about 2/3 of them, over a few months, before they were all pulled. Just for my personal use at some future date. I would suggest doing the same for any site that has such technical details. I assume some accountant or intelectual property rights lawyer comes along and says "remove that content" from open access that some well meaning technician had put up there. -- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on http://home.graffiti.net/diverse:graffiti.net/ or quite likely being removed from site/s because of some health and safety consideration |
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