Boss - TW-1 issue
- Stevenrb718
- Breadboard Brother
I have a Boss TW-1 that doesn't power up. The bypassed signal is always present. The LED doesn't light, but the momentary switch is tested good. The thing that confuses me is when checking voltage throughout the pedal, the points show no voltage in relation to the ground. 9V is on many points in relation to the negative battery terminal however. I'm not sure if this is a normal feature of an 80s Boss ACA pedal.
- x-tn
- Breadboard Brother
- Stevenrb718
- Breadboard Brother
I'm not looking to mod it to PSA specs, I'm looking to diagnose why the pedal isn't working.x-tn wrote: ↑23 Jan 2021, 13:12 http://stinkfoot.se/archives/1019
https://www.audioservicemanuals.com/b/b ... -schematic
- plush
- Cap Cooler
Are you measuring it with the input jack connected? Disconnecting input jack terminates power supply's path to ground (this is made to stop battery from draining when there's no cord plugged in). Plug input jack and re-measure.Stevenrb718 wrote: ↑20 Jan 2021, 17:05 The thing that confuses me is when checking voltage throughout the pedal, the points show no voltage in relation to the ground. 9V is on many points in relation to the negative battery terminal however.
- Stevenrb718
- Breadboard Brother
Yes I am, and the wiring for the plug detection seems to be correct according to the schematic. Now on-board function of the detection circuit I'm not sure.plush wrote: ↑23 Jan 2021, 17:17Are you measuring it with the input jack connected? Disconnecting input jack terminates power supply's path to ground (this is made to stop battery from draining when there's no cord plugged in). Plug input jack and re-measure.Stevenrb718 wrote: ↑20 Jan 2021, 17:05 The thing that confuses me is when checking voltage throughout the pedal, the points show no voltage in relation to the ground. 9V is on many points in relation to the negative battery terminal however.
- x-tn
- Breadboard Brother
The page I linked says:Stevenrb718 wrote: ↑23 Jan 2021, 17:07 I'm not looking to mod it to PSA specs, I'm looking to diagnose why the pedal isn't working.
"some of the older Boss pedals (those with an ”ACA” sticker by the adapter jack) won’t work right with a normal 9vDC power supply. Keeping them on a daisy chain supply, with power and signal cables connected to at least one normal (PSA) pedal makes them light up, but in all other instances they need 12 volts DC on the adapter jack."
And you talk about 9V in your initial post. I thought you try to power it with 9V and it doesn't work because of that.
- Stevenrb718
- Breadboard Brother
I got ya. No, my reference to 9V was knowing that the ACA pedals take a 12V supply and regulate it internally with the resistor/diode. I actually have an ACA spec adapter. Unfortunately, the pedal has the same problem regardless of power supply. I was just questioning why voltage tests were showing relative to negative circuits rather than ground. I do appreciate the ideas.x-tn wrote: ↑23 Jan 2021, 21:54The page I linked says:Stevenrb718 wrote: ↑23 Jan 2021, 17:07 I'm not looking to mod it to PSA specs, I'm looking to diagnose why the pedal isn't working.
"some of the older Boss pedals (those with an ”ACA” sticker by the adapter jack) won’t work right with a normal 9vDC power supply. Keeping them on a daisy chain supply, with power and signal cables connected to at least one normal (PSA) pedal makes them light up, but in all other instances they need 12 volts DC on the adapter jack."
And you talk about 9V in your initial post. I thought you try to power it with 9V and it doesn't work because of that.
- CheapPedalCollector
- Resistor Ronker
Post some pics of the circuit board.
- x-tn
- Breadboard Brother
Stevenrb718 wrote: ↑20 Jan 2021, 17:05...the points show no voltage in relation to the ground. 9V is on many points in relation to the negative battery terminal however.
There is a 470ohm resistor and a diode between the GND and the power input negative. The schematic is not so clear but I think they are R48 and D8. One or both of them should be failing. You can try to measure them without removing. Just don't plug a jack on the input while measururing them.Stevenrb718 wrote: ↑23 Jan 2021, 22:07I was just questioning why voltage tests were showing relative to negative circuits rather than ground. I do appreciate the ideas.