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Forums - Synths & synthesis
Subject: Knob Prob.
Original Message 1/13 30-Mar-00 @ 02:00 PM - Knob Prob.
Just got my 303 at a vintage shop in Tokyo (the shop has one more if anybody's interested). It's generally in great condition and I'm very happy, but there is a bit of a problem with the ENV MOD knob. When tweaking, of course, rotating the knob gives the desired effect, but moving the knob in other directions (say to the left, right, in or out) is unavoidable. If, for example, while tweaking, the knob gets pushed to the left a little, I get additional unwanted noise and the ENV MOD level seems to temorarily go to zero. After further experimention, I found that if I hold it to the right side and tweak at the same time, the problem disappears. Has anyone encountered this problem before and/or know what to do about it?
Message 2/13 30-Mar-00 @ 02:00 PM - Knob Prob.
Just got my 303 at a vintage shop in Tokyo (the shop has one more if anybody's interested). It's generally in great condition and I'm very happy, but there is a bit of a problem with the ENV MOD knob. When tweaking, of course, rotating the knob gives the desired effect, but moving the knob in other directions (say to the left, right, in or out) is unavoidable. If, for example, while tweaking, the knob gets pushed to the left a little, I get additional unwanted noise and the ENV MOD level seems to temorarily go to zero. After further experimention, I found that if I hold it to the right side and tweak at the same time, the problem disappears. Has anyone encountered this problem before and/or know what to do about it?
Message 5/13 31-Mar-00 @ 05:49 AM - RE: Knob Prob.
Hi,
Having just got a damaged TB303 myself, I discovered that Roland made a rather unfortunate decision to simply mount the pots to the PCB without bolting them to the chassis in any way (saving costs). Any pressure on the knobs can so easily break the solder connections or damage the PCB - in my tb303 I just had from Japan, the pcb was completely cracked in half because someone bashed the mode rotary switch.
As you have to hold the knob to the right to make it function correctly, this suggests a simple cracked solder joint and therefore it will probably be very easily repaired. The noise is being caused by the bad connection making and breaking contact as you twiddle the knob. When it goes to zero, it is breaking contact altogether.
The problem *could* also be the pot itself but a simple bad solder joint is more likely.
I build tb303 clones and I can carry out extensive repairs on these machines (as I am having to do with mine). If you would like me to sort out the problem for you, I would do it for very little because it is so simple. You would need to pay postage to and from UK.
As an alternative, whip off the back cover and grab your nearest soldering iron. Melt the solder joints for the env mod knob. Simple! I doubt your local telly repair shop would charge much to do this for you, if you would rather not do this job.
Trev
Having just got a damaged TB303 myself, I discovered that Roland made a rather unfortunate decision to simply mount the pots to the PCB without bolting them to the chassis in any way (saving costs). Any pressure on the knobs can so easily break the solder connections or damage the PCB - in my tb303 I just had from Japan, the pcb was completely cracked in half because someone bashed the mode rotary switch.
As you have to hold the knob to the right to make it function correctly, this suggests a simple cracked solder joint and therefore it will probably be very easily repaired. The noise is being caused by the bad connection making and breaking contact as you twiddle the knob. When it goes to zero, it is breaking contact altogether.
The problem *could* also be the pot itself but a simple bad solder joint is more likely.
I build tb303 clones and I can carry out extensive repairs on these machines (as I am having to do with mine). If you would like me to sort out the problem for you, I would do it for very little because it is so simple. You would need to pay postage to and from UK.
As an alternative, whip off the back cover and grab your nearest soldering iron. Melt the solder joints for the env mod knob. Simple! I doubt your local telly repair shop would charge much to do this for you, if you would rather not do this job.
Trev
Message 6/13 31-Mar-00 @ 11:51 AM - RE: Knob Prob.
I appreciate your response Trevor. My roommate and I opened it up and took a look. Unfortunately we didn't have a soldering iron handy, but will pick one up tomorrow. My roommate is some sort of an engineer and might be able to pull it off.
Because we are not skilled electricians, I have a few other questions before we bust out the soldering iron and wreck this thing. I am assuming that we have to melt the solder connecting the ENV MOD knob to the board and pull it off. After that, I assume we have to take off that copper colored thing at the bottom of the connection. Would that be the pot?
The actual connection to the board is not loose -- it's the interior connection between the knob shaft and the pot(?) It seems almost as if the knob shaft is stripped. If that is the case, is the shaft replaceable?
Once again, thank you for your time. I have a two week warranty on the machine and want to find out everything I can before the two weeks runs out. I would hate to have to return it if there is serious problems, but it was expensive enough without having to pay to get it fixed or send it abroad.
Because we are not skilled electricians, I have a few other questions before we bust out the soldering iron and wreck this thing. I am assuming that we have to melt the solder connecting the ENV MOD knob to the board and pull it off. After that, I assume we have to take off that copper colored thing at the bottom of the connection. Would that be the pot?
The actual connection to the board is not loose -- it's the interior connection between the knob shaft and the pot(?) It seems almost as if the knob shaft is stripped. If that is the case, is the shaft replaceable?
Once again, thank you for your time. I have a two week warranty on the machine and want to find out everything I can before the two weeks runs out. I would hate to have to return it if there is serious problems, but it was expensive enough without having to pay to get it fixed or send it abroad.
Message 7/13 31-Mar-00 @ 02:02 PM - RE: Knob Prob.
Hmmm. The pot is the whole rotary control, it seems like the carbon track inside the pot has worn away. Unfortunately these Alps pots have been discontinued and are VERY difficult to repair (some would say impossible). You may be lucky and find something compatible or you could try Analogue Solutions here in the UK - I know they had a few spares some time ago. I can't remember if a 606 instrument level pot is the same value, if so you could try that since 606's are cheaper and easier to find.
Message 8/13 02-Apr-00 @ 07:05 AM - RE: Knob Prob.
Yup! The 606 level pots are 50k log. The same goes for the 303 Env Mod knob.
(According the 303 service notes it's a 50k lin pot, but it's one of the many mistakes)
(According the 303 service notes it's a 50k lin pot, but it's one of the many mistakes)
Message 9/13 02-Apr-00 @ 07:57 AM - RE: Knob Prob.
Please don't attempt to remove the pot yourself, without the appropriate solder 'sucker' tool or otherwise. Attempting to yank off the pot whilst melting the solder will certainly damage the pads on the PCB. You don't want this, especially with a tb303!
Before you do anything else, remelt the pot's solder connections. Bad/ loose joints are often quite invisible. Try this first, and see what happens.
Trev
Before you do anything else, remelt the pot's solder connections. Bad/ loose joints are often quite invisible. Try this first, and see what happens.
Trev
Message 10/13 07-Apr-00 @ 03:37 AM - RE: Knob Prob.
The best thing to do is to get a
DE-Soldering iron, it makes life so
much easier when removing pots
and chips.
As far as the carbon track, it is
possible to clean it. My 303 had a
"scratchy and noisy" cutoff knob! Talk
about the most crucial part of the
303. I was not able to find one
anywhere, so I decided to fix it
myself, with some tips from Robin
Whittle.
It was a fairly easy task and can be
done in like 20 minutes. The other
pots on the 303 could possibly be
interchanged with a 606. Also the
company called "BiAmp" had some
similar pots in stock. But they were
for a dj mixer I was fixing once.
Hope you get your 303 up and
running!
909 Inc.
DE-Soldering iron, it makes life so
much easier when removing pots
and chips.
As far as the carbon track, it is
possible to clean it. My 303 had a
"scratchy and noisy" cutoff knob! Talk
about the most crucial part of the
303. I was not able to find one
anywhere, so I decided to fix it
myself, with some tips from Robin
Whittle.
It was a fairly easy task and can be
done in like 20 minutes. The other
pots on the 303 could possibly be
interchanged with a 606. Also the
company called "BiAmp" had some
similar pots in stock. But they were
for a dj mixer I was fixing once.
Hope you get your 303 up and
running!
909 Inc.
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