Hi I was just wondering if someone can help with a problem I am having with this amp, it has over time developed a crackling volume control.
I know this is a common fault with amplifiers of this age but I would like too replace the pot if possible, rather that using contact cleaner, off course I’m not very knowledgeable about these things which is why I came here for help. I am just not sure what part to get is there an exact replacement the label on the pot says qvz-1219-005,m250kohmbx2,583L A. If it is not possible too get this part or similar and I have to use contact cleaner which do you recommend? Thank you..
Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
I know this is a common fault with amplifiers of this age but I would like too replace the pot if possible, rather that using contact cleaner, off course I’m not very knowledgeable about these things which is why I came here for help. I am just not sure what part to get is there an exact replacement the label on the pot says qvz-1219-005,m250kohmbx2,583L A. If it is not possible too get this part or similar and I have to use contact cleaner which do you recommend? Thank you..
Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Service Manual free download,schematics,datasheets,eeprom bins,pcb,repair info for test equipment and electronics
Wouldn't recommend 'Super Servisol 10', it's useless.
If you can get Philips 390CCS then that was quite good.
The Americans had the best stuff, it was called 'Blue Stuff' but probably not available any more, perhaps our American pals can tell us?
If you can get Philips 390CCS then that was quite good.
The Americans had the best stuff, it was called 'Blue Stuff' but probably not available any more, perhaps our American pals can tell us?
Thanks toprepairman how about this stuff Caig Deoxit D5 Contact Cleaner a lot of people say it's quite good. But at twenty pound a can it's a bit pricy, probably more than the replacement part might cost.
Is there no one here that can tell me the part I need.
The amp was made in 1978 but has an amazing transparent sound and good stereo imagery.
Is there no one here that can tell me the part I need.
The amp was made in 1978 but has an amazing transparent sound and good stereo imagery.
Depending on the internal arrangement it may be possible to fit an Alps Blue.
Can't remember if the original was a special, in which case it is unlikely you'd get another.
Can't remember if the original was a special, in which case it is unlikely you'd get another.
Looking at it again it's a dual pot with six lugs at the bottom and two at the top (one on each barrel) probably for the loudness switch. The bx2 at the end of the number might mean dual, does the B mean linear?
It'll be a log pot, and you're correct with the two extra lugs being for 'loudness'.
Most Alps blues also have the extra pin connections for loudness so you should be Ok there.
Most Alps blues also have the extra pin connections for loudness so you should be Ok there.
I really appretiate your help toprepair man, I'm almost ashamed to say but after spraying with some servisol super 10 switch contact cleaner there is no more crackle at all. but am having trouble getting the centre voltage to balance up even after spraying them it has no effect the reading seems to be all over the place the manual suggest to adjust them below +/- 10 mv but at switch on one channel reads 68mv then climbs down after 15 mins then up to - 28 the slightest adjustment tends to make them move alot do i need to replace these. The manual says these are 220ohm 0.15 W Variable carbon R311 and R312.
What would be a high quality replacment, I heard ceramic are good but have no idea which ones to buy. Thanks.
What would be a high quality replacment, I heard ceramic are good but have no idea which ones to buy. Thanks.
No probs with the servisol 10, if it worked then that's just fine.
You should be Ok with any replacement trimmers, the cermet ones will certainly work fine. You're unlikely to get something to fit right in but if you extend the pins with something like 22 gauge wire then that will work.
Regards
Henry
Ps. If you're in the south east, try visiting then Audiojumble at Tonbridge this Sunday.
You should be Ok with any replacement trimmers, the cermet ones will certainly work fine. You're unlikely to get something to fit right in but if you extend the pins with something like 22 gauge wire then that will work.
Regards
Henry
Ps. If you're in the south east, try visiting then Audiojumble at Tonbridge this Sunday.
Those trim pots are usually very reliable.
Check boards for crook solder joints especially on the output ic's pins and throughout the driver stage.
My preference is to just blanket resolder the power amp stages, also resolder the regulator stages.
This has cured thousands of amplifiers for me with 100% reliability.
Eric.
Check boards for crook solder joints especially on the output ic's pins and throughout the driver stage.
My preference is to just blanket resolder the power amp stages, also resolder the regulator stages.
This has cured thousands of amplifiers for me with 100% reliability.
Eric.
Yep looks like i have to do what you say about the soldering,would be nice if i can change the trimmers at the same time as the slightest touch can send them of up to 20mv do the resistance and wattige have to be exact. I would like to change them with ones that have a finer adjustment.
Will any of these do..
54mm pitch, 2 Way Single Row Right Angled PCB Socket 254mm Pitch - 3 Way Single Row Right Angled PCB Socket 254mm Pitch - 4 Way Single Row Right Angled PCB Socket 254mm Pitch - 5 Way Single Row Right Angled PCB Socket 254mm Pitch - 10 Way Single Row
They actually look similar if not exact to the secound one down only are 9mm in size on the amp. Thanks.
If the link dosen't work just paist this in the search box. 220ohm 9mm cermet trimmer
Will any of these do..
54mm pitch, 2 Way Single Row Right Angled PCB Socket 254mm Pitch - 3 Way Single Row Right Angled PCB Socket 254mm Pitch - 4 Way Single Row Right Angled PCB Socket 254mm Pitch - 5 Way Single Row Right Angled PCB Socket 254mm Pitch - 10 Way Single Row
They actually look similar if not exact to the secound one down only are 9mm in size on the amp. Thanks.
If the link dosen't work just paist this in the search box. 220ohm 9mm cermet trimmer
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Just do the resoldering first - Dc offset trimmers are usually quite tricky to set to exact 0v - this is normal.
Eric.
Eric.
Okay so i did the resoldering turned it back on and checked the channels. Both started at 55mv and quickly dropped, after 15mins both channels were reading below 5mv and stayed there well within spec guess there must have been a dry point some where. In future i will check this first thank you so much for all your help.
Well done there Eric for the good advice.
Must say I'm surprised not to have run into that problem myself but there isn't that much JVC kit floating around here.
Must say I'm surprised not to have run into that problem myself but there isn't that much JVC kit floating around here.
Sorry guys i know this is an old thread and it has been a while, but it seems that this volume pot has finally given up the ghost and is causing tons of distortion looking around i can seem to find similar looking pots, but i am still confused as to whether this is logarithmic or linear the b in the name has opposite meaning when it is America to Europe. So what would it mean in Asia. Where i suppose there meaning is the right one. This is the UK version model by the way.
I would like to get fairly close to it having loudness and the same split shaft and size.
I would like to get fairly close to it having loudness and the same split shaft and size.
Attachments
Right - all bets are off regarding potentiometer log. law as soon as you deal (as is inevitable for tapped pots) with any Asian manufacturers. As before, it's a log. taper type B and you can buy from a few manufacturers but the most accessible high quality products in 1-off qty will be ALPS and they are available in genuine, fake, 😉 standard or tapped forms if you search thoroughly.
I have used this German agent before when I needed specific hard-to-find parts. A little expensive, but quality. Price list for ALPS Japan Products: Potentiometer, Slide Potentiometer, Fader knobs, logarithmic, linear, data sheet
There is at least one UK supplier of a smaller range, however.
There are also problems with the format of Alps RK27 "Blue velvet" pots. 4 pin tapped pots have all pins in line and you'll need to adapt a lead to this 4th pin and bend it flat to allow the pot to fit the PCB. Like the code suggests, they're 27mm sq. See pic.
Pots like your JVC type are large, 24 mm dia. but they disappeared decades ago, only some specialty parts remaining. 16 mm dia. pots are still made but new products now use even smaller pots.
This Ebay item looks tempting even if it is doubtful, Copy ref. no. to your browser: 130820551892
Beware of shaft lengths and types, they are not adjustable or available in any choice of length for spline types at least.
I have used this German agent before when I needed specific hard-to-find parts. A little expensive, but quality. Price list for ALPS Japan Products: Potentiometer, Slide Potentiometer, Fader knobs, logarithmic, linear, data sheet
There is at least one UK supplier of a smaller range, however.
There are also problems with the format of Alps RK27 "Blue velvet" pots. 4 pin tapped pots have all pins in line and you'll need to adapt a lead to this 4th pin and bend it flat to allow the pot to fit the PCB. Like the code suggests, they're 27mm sq. See pic.
Pots like your JVC type are large, 24 mm dia. but they disappeared decades ago, only some specialty parts remaining. 16 mm dia. pots are still made but new products now use even smaller pots.
This Ebay item looks tempting even if it is doubtful, Copy ref. no. to your browser: 130820551892
Beware of shaft lengths and types, they are not adjustable or available in any choice of length for spline types at least.
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Have you tried opening the old pot up by bending the tags on each gang ? Nothing to lose now its out. As long as the two halves separate easily you should be able to clean it using a cotton bud on the resistive track and wipers. Use ISO and wash all the old gunk out. Retension the wipers if needed and also bend them a little to one side so they sweep unused track. I've done hundreds of similar single gang pots over the years on TV's and the like. Squirting with cleaner is only a temporary fix at best, open it up and repair it and they are as good as new.
Thanks Ian i looked at that sheet and he does not seem to have the right shaft, neither does that other link the other Alps i have found 221127808523 seems closest to what i need but it has no loudness. How well do these Chinese knock offs work compared to the real thing would it perform better than the original JVC part did when it was new? The shaft on mine 25mm x 6mm. Thanks for helping.
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