Old Japanese Boss TW-1 in need of repair

[Slowpoke101]

OK. It is almost certain that a better connection is required for the negative (black) probe. Is there any way that you can measure the voltage between pins 4 and 11 of the IC?

Edit: Considering the age of this pedal it would be a good idea to carefully remove the input and output sockets and clean the areas where they contact the mounting holes in the enclosure. This includes the threaded sections of the sockets themselves. They may not be making very good contact after all this time.
I also suggest that you also check R49 (4K7 resistor) that is attached to the sensitivity pot. It appears to be mount directly to that pot and not on the circuit board so it must be grounded via the pot. Remove the pot and clean its mounting points too. Do be careful doing all this. It may not make any difference but it might.

[AM]

I took everything apart and cleaned it. I also cleaned the circuit board.
Voltage between +Vs and -Vs is 1.80 (I assume those are pins 4 and 11).
Other voltage measures between the places cables connect to the circuit board and ground (numbers as shown at schematic) are:
1,2,3,4,5,9,14,15=0
6,7=0,80
8=0.30
10=1.85
11=4.44
12=6.57
13=2.08
16=2.95
17=5.97

[Slowpoke101]

It is a bit disappointing that cleaning up those points of contact didn't help but those voltage measurements that you supplied certainly do help with working out what is going on. Great work. There is good news with the documentation that you are working with - even though it is for the two chip version of the TW-1 there is very little difference between that version and the single chip version. The circuit references are almost the same as to make no difference. The circuit board track routing is almost the same as well with only a few minor changes to accommodate the power rails for the chips.

Now what do your measurements tell us - Firstly, your 9V battery is going flat or the power socket is faulty. You only have 6.75V on PCB pin 12 to ground (ground is to case from pin 14 via the input socket and your dummy plug). Also with PCB pin 13 being at 2.08V  and not near 4.5V Vref is also now very low as well. The input socket is also the on/off switch for the effects pedal but I would not have anticipated it to have drained its battery this quickly. Anyway just for your info - PCB pin 12 is the 9V input into the board. Pin 14 is the main 0V or ground connection. One silly question regarding the dummy plug - it is a mono type and not a stereo type? I've had that happen.

The next test to do is to set your multimeter to a low resistance test (continuity test if you wish - beware this can be misleading, you still need to look at the measurement not just listen to the meter)/ Place the probes together and make certain that the display shows zero (or close enough to it). This test is to see if the power tracks to the IC are OK. Remove any power for the pedal. Connect the black test probe to the pedal case and the red test probe to pin 11 (-Vs) of IC1 - the meter should read zero. If doesn't just keep going. Now remove the test probes and place them as follows; place the red probe on PCB pin 12 and the black probe on pin 4 (+Vs) of IC1 - the meter should read zero. If doesn't, keep the black probe on PCB pin 12 but following circuit track from pin 4 of IC1 place the red probe on the next available soldered point until the meter reads zero. Keep following the track back to the black probe, you are looking for a possible broken circuit board track. Let us know what you find.

The following image may be of some assistance or it may be of some extreme confusion. The positive pad of C23 (100uF/16V) is quite fragile in its physical design and is easy to damage. It is possible that the track leading of to IC1 has been severed. Refer to the image. I have marked soldered connections in red that should have 9V on them.



Click on the image for a larger version to download or whatever it does. One day I may remember how to resize these things but medical issues are causing memory errors.

[AM]

Thank you so much!
The dummy plug is mono.
Continuity test: meter at pin 11 reads 0.8 and there is a beeping sound.
By pin 12 you mean +in (C) or +in(D)?

[Slowpoke101]

Pin 12 of the flying wires terminating to the PCB. Not the IC.

[AM]

I tried to troubleshoot the DC-in jack after what you wrote about possible damage. So I attached the same battery straight to the pedal's snipped battery cables and now I get a diifferentvreading between pin 12 and ground. It's 8.28 V and not the 6.57V I get when I connect it to the D.C. Jack.

[Slowpoke101]

If you attach a 9V battery directly to an old Boss's DC input jack the pedal will either work poorly or it will not work at all. The old pedals require the adapters that output close to 12V DC. 9V DC will not work correctly. Why? Look at the circuit diagram and find D8 and R48 (470R). These are for polarity protection and hum reduction. It also causes the 9V adaptor got-cha trap. When using a 9V battery you must use the internal battery connections. There is most likely nothing wrong with the DC input jack.

[AM]

OK, I connected the battery back to the DC in which supplies 6.57V tonpin 12.
Measured voltages between every red marked connection on your photo and ground. I get a 6.5V reading on all of them except the top left two that are connected to IC's pin 4 where I get 1.81V. Please note that on out (B) (pin 7?) I get 6.5V like on all the other red marked spots.

[Slowpoke101]

I suggest trying your old Boss DC adaptor to see if you can get the correct voltage but first try the following.
Solder an insulated wire to the two points as shown in the following image and test the marked points again. See if the voltages have come up at all.

[AM]

"Yellow" cable test didn't make a difference.
Roland ACA adaptor (measured output 14.78V) upped voltages to 10.80 V on all previous spots where I was getting 6.5V before but made almost no change on pin 4 and thevtwo other red spots connected to it, giving me just 1.91V.

[Slowpoke101]

Connect the end of the "yellow" cable closest to pin 4 of IC1 directly to pin 4 of IC1 and try again. The results that you got from the Roland adaptor is to be expected and is good. Nothing to be concerned about at the moment.

[AM]

Back on battery power. I followed your instructions and now voltage on pin 4 went from 1.81V to 5.22V!

[Slowpoke101]

Good. Now how are you arranging the battery power? Is it via the pedal's internal battery wiring or by plugging into the DC jack?
Also, now that you have slightly higher voltage on pin 4 of IC1 what are the voltages on the other pins of IC1?

[AM]

I connect the battery via the DC jack.
I'll measure voltages on all other IC pins and give you a detailed report tomorrow.
(I live in Europe and it's 1:30 in the morning right now).
Thanks for guiding me through this!

[Slowpoke101]

No problem. I'm in Australia EST so it's nearly Midday (actually it's 11:42AM).
Just remember that when connecting a 9V battery via the DC jack it will not supply enough voltage to power an old Boss effects pedal. You have to use an old Boss ACA plug pack or use the pedal's internal 9V battery wiring. It's annoying to say the least.
Anyway, I will be very interested to see the results tomorrow.


Edit: There is a way to modify the pedal to use 9V DC via the DC jack but I can only recommend doing this as a temporary measure. It involves simply shorting out D8 and R48. It is quite simple to do and involves installing a wire link. Refer to the following image;



The yellow "wire" is soldered across the two points shown and that is it. The pedal can now accept 9V but do not plug in an old ACA type adaptor without removing the link. That would be to much voltage for any 16V capacitors in the pedal.

[AM]

I'm back. So, with the old Roland ACA power supply and with a wire connecting IC's pin 4 to the positive leg of the capacitor you you highlighted I'm getting the voltages written with pencil on the inside of the IC drawing I'm attaching.

[Slowpoke101]

Now these voltages are very interesting. There should be the same voltage on pin 10 as there is on pin 5. The circuit shows that they are both directly connected to Vref so make sure that there are no damaged tracks going to either pins. But pins 11, 12 and 13 are really concerning. They should all be near 4V but they are not.
Possible culprits could be C15 could be short circuit. It is a tantalum type and it is more than old enough to be doing tantalum's favourite little habit of going short circuit for no reason, assuming that you haven't replaced it earlier. D6 or D7 could be open circuit. R29 (1K) could be open circuit. R29 (100K) could be open circuit - yes I know that I wrote R29 twice, look at the circuit diagram, that's what it says. The "Drive" switch may be faulty - going open circuit. And lastly on the list of possible culprits is IC1 itself. I would start with C15 and the IC1 - use a TL074.

You are really making progress with this old unit now and are getting close to getting it work. Don't rush it

[AM]

I checked C15. I have replaced it already. Please have a look at the photo I'm attaching.
I checked with my multimeter on C15 and R29. The legs that are towards the end of the board give me 0.5 and the beeping sound. The legs towards the IC nothing...well just 1 and no beeping sound. The only IC pin that gives 0.5 and sound is -Vs.

Most likely irrelevant to troubleshooting, but since we are at it, is there a desired position on the trimpot? I have it somewhere halfway now but don't remember where it was stock.
Edit: I can't attach the image but I hope my description regarding which legs give what measurements is clear.

EDIT 2: I found a workaround for the image upload. Please check this link to see if there is anything wrong with C15's polarity. I've checked all other replaced caps' polarity and they are OK but the tantalum marking on the PCB differs from the electrolytic ones.
https://ibb.co/Ctbm9Yp

[AM]

After further probing I found out that the two legs of C7 (cap to the top right of inductor) were connected via excess solder. I'm guessing they shouldn't so I removed the solder and I will also solder a short solid core wire between the negative leg of C7 and R10 because the trace has been lifted a bit and needs to be secured. No difference in voltages or sound even after what I just did though.

[Slowpoke101]

From your picture of C15 you do have its polarity correct. Tantalums can be confusing as to their polarity. Also I think that the R29 that is mark as 1K as shown on the circuit is actual shown as R27 on the overlay. I may have read that somewhere as well but forgot about it. R29 is the 100K. Not that it matters at this time.

The setting of VR3 (trimpot) is shown in the service note (the image with the circuit and overlay) which is not really helpful unless you have some calibrated audio signal generators available. If you have moved it already and cannot remember the original setting just set it to the midway position for the moment. Get the effects unit to work first then worry about fine tuning it later.

Good idea to check the excess solder on C7. You never know what can be hidden underneath. I am concerned about track damage to this circuit board. Is there any way that you can upload a picture of the solder side of the circuit board so I can check for anything obvious?

Some voltage checks. Black probe to ground (case). "Drive" switch set to DOWN, measure the voltage on IC1 pin 12. Then pin 13 and pin 14. Now set the "Drive" switch to UP and measure pins 12, 13 and 14 again. Now leaving "Drive" set to UP and the black probe still on ground measure the voltages on both legs of R27 (refer to the overlay) and then both legs of R29.