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am i screwed?
- Thread starter redname
- Start date
I’m sure everyone will need more info. Bass make, model etc. Even pictures.
it's a yamaha TRB6ii
here's the story
put in the battery at the wrong polarity, plugged in my cable and has no sound and later realised it's the wrong polarity, corrected it and now it emits a high pitch sound
The preamp in that bass has a voltage doubler circuit (it creates +9v & -9V). There is an IC (TC7662 or ICL7662) and some capacitors which would get damaged with reverse voltage. Hopefully only that section of the circuit is damaged.
You would need an electronics technician/repairman to repair it. A luthier with basic electronics knowledge might not be able help you.
Also search and find the 'Yamaha TRB 6II Service Manual' pdf. It will help with the repairs.
Good info. D5 would shunt the battery if reversed, and would likely be the first to go if the condition lasted long enough. An easy way to check if D5 is damaged is to simply measure the battery voltage with the battery attached and the cable plugged in to turn on the preamp. If D5 is blown, it'll be a short and the battery will measure very low.
I'm surprised there isn't a reverse polarity protection diode on that preamp. Most have one for that very reason, even though it reduces the supply voltage from the battery a little bit.
Good info, too. I didn't notice the D5 when I had a quick look at the schematic. According to the service manual it's 1SR139-100 and it's datasheet states 'Maximum Repetitive Peak Reverse Voltage: 100V'. So, it shouldn't blow with 9V but...
I'm surprised it's possible to insert the battery in reverse position. I have a Yamaha BB bass and it's not possible to insert a reverse battery in the battery box.
The reverse voltage is 100V, but it's in forward conduction mode when the battery polarity is reversed. Forward voltage is 1.1V, so in that condition, it'll draw as much current as the battery will give it to drop the battery voltage from 9V to 1.1V. That's probably a lot more than the 1A continuous forward current rating. The peak current rating is 40A, but that's for a very brief period of time. I didn't look at any graphs, but peak current is likely in the usec or maybe msec range.
It would take some doing to get a battery connected backward in my BB5000A, but I wouldn't rule it out of possibility. The tabs around the terminals could be broken or otherwise not functional.
Still confused as to how the battery is installed with reverse polarity. Was it wired in wrong?
9V batteries have very different terminals to avoid this.
9V batteries have very different terminals to avoid this.
Some battery terminals won't click in. I have a Yamaha Attitude Custom, that I can install the battery w/ reverse polarity.
I have a Fender Jazz Bass 24 that has a battery box that could allow a “backwards install”.
These are known to cook the pre-amp if you do reverse it. I’m always very careful to make sure I don’t mix it up. It spent several years with the pre-amp and pots removed, so I didn’t have to worry, but now it’s re-installed again.
These are known to cook the pre-amp if you do reverse it. I’m always very careful to make sure I don’t mix it up. It spent several years with the pre-amp and pots removed, so I didn’t have to worry, but now it’s re-installed again.
The voltage doubler failing would probably be a good reason why that preamp is whistling now. The Yamaha preamp will whistle on a dying battery before it goes completely dead... Both my Yamaha TRB1005j and TRB5P do that.
You're right.
Too many reverse things...This is the box in my Yamaha. The fins around the (+) spring makes it difficult to insert (-) battery terminal there. But apparently if you try to shove it you might.
yes
thanks, let me get this message to the tech and see what he says
great info, thanks
You're right.
This is the box in my Yamaha. The fins around the (+) spring makes it difficult to insert (-) battery terminal there. But apparently if you try to shove it you might.
View attachment 5328854
yap, tht's what happened
yap, the bass is active, so it can only have sound with batteries
