Roland TR-606 hum when LEDs are on ...

[tenga]

Hi eveyone !

i got a roland tr606a while ago it lights up and make sound on batteries but i have some issues when i use a power supply.

-when powered on Roland dc adapter it makes a buzz noise when the leds are on.
-ive tried other dc adaptors , but they work fine on my 303 !!
-the more leds are lit stronger the noise.
-the noise is louder on the headphone output than on the line out
-the noise is louder when the volume pot is close to zero and decreases when up.

what ive tried so far:
-replaced electrolitic caps on the power supply c104 c105 c101 c100
-unmounted vr8 and cleaned it.
-replaced q42 & q4
-replaced q403 q404 q405 q406 q407 q408 q409 q410 a411 q412.
( i suspected the noise came from led/buttons matrix)

i found the noise sometimes temporally go away when moving q100 & q101

im pretty desperate , anyone has any idea what can be wrong ??
i have scope , signal generator , multimeter and all needed to solder/unsolder.
best regards
chriss

[James Perrett]

Try hooking up the scope to the internal power supply tracks and checking to see whether you see ripple when the LEDs are on. Are you using the correct power supply?

[tenga]

Hi James:

thanks for your anwswer !!! i realy appreciate it !!

yes im using the right power supply: original boss 9v dv , works perfect with sh101, tb303 and mc202.

ive done some scope on the power supply , yes there is high frequency ripple
and the amplitude changes depending on the location.

its present even in very early stages of the power supply.
should i do it on ac or dc mode?

[Folderol]

Is the hum actually 50Hz, or does it sound more like 100Hz. It should be 100Hz, otherwise it may be the mains transformer has an open circuit secondary winding which will sag more under load, as well as having a higher ripple.

Alternatively it could be something in the unit drawing more power than it should and dragging the supply down.

Do you have the correct PSU. I believe that the correct current rating is quite critical.

[ef37a]

IMHO the first thing to check is the open circuit output voltage of the supply.
The filter caps might be fine but the regulator, assuming it has one, might be faulty and the series control transistor has 'punched thru' and is letting raw, unregulated current through. This will have a lot of load dependent ripple on it and be 12 or even more volts and that could cause damage.

We know the supply should deliver 9V but what is the current rating? A modern switch mode PSU rated at 9V and two amps say will not be expensive, why faff about with the old one?

There is are possible problems with a new, generic supply.
1) The co-ax connector might not match.
2) The polarity might be wrong. Many 9V supplies are intended for guitar pedals which are historically and annoyingly silly centre negative.

Solution? Chop the original plug off and splice it to the new PSU. Bit O heat shrink taking great care to get the polarity correct!

https://www.amazon.co.uk/Multibao-2000m ... 8963&psc=1 e.g.

Dave.

[tenga]

Thanks for your reply Folderol !!
greetings from France !!

>>Is the hum actually 50Hz, or does it sound more like 100Hz
to be honest i didnt check the frequency , but i can check tonight.

>>Alternatively it could be something in the unit drawing more power than it should and dragging the supply down.

this do make sense... the noise only come up when the leds are on.
the more leds are on , the louder the noise.
when a led blink so does the noise.

this is why i checked the led matrix so much and changed the transistors on it.. unfortunatelly no luck so far... but i agree something might be drawing abnormal power , i just dont know what it is....

i could run a spray frezze or isopropilic alcohol test to find the hot zone.

>>Do you have the correct PSU. I believe that the correct current rating is quite critical.

i will post my current model number tonight.

[tenga]

Hi there:

i found the model of my Power supply in the order from a few years back.

i am using a Boss PSA 230S power supply, these are the specs :
9 V DC
500 mA
Negative polarity inside
Inside: 2.1 mm
Outside: 5.5 mm

note from manual: Suitable for all BOSS Compact and Twin pedals with a 5.5 x 2.1 mm hollow plug socket, negative polarity inside, ME-50/-20/-20B multi-effects, the DB-66/-88/-90 metronomes, DR series drum machines, FC series foot switches, MC-202, SH-101, SP-202, TR-626 and all TU series tuners.

do you think its suitable ?

bets regards
chriss

[Folderol]

Check that there is 6V from Q42 emitter to the +6V point. i.e. across C105.
Also, the external PSU must NOT carry an earth through as that would either short out the voltage regulator, or destroy Q41, and could cause all sorts of problems as it could possibly overvolt everything!

[Wonks]

The TR606 is designed to use the Boss ACA adapter, which could be some of the reason for your issues. This is an unregulated 12V DC PSU and the TR606 drops the voltage internally to 9v.

With a 9v supply, the voltage might be too low.

Have you tried it with batteries? That removes any PSU issues.

[tenga]

>>Have you tried it with batteries?
yes , with batteries it works good.
what you say makes sense...

i fond more info about the difference between ACA and PSA adators:
its in french thought.
i was not aware the power supplys were so different !!!

https://fais-tes-effets-guitare.com/boss-aca-vs-psa/

[Wonks]

Yes, they are quite different!

[tenga]

the thing tha puzzels me it why does it works good on the 303 ?? and has issues on the 606 ??

Folderol might be right , something might be drawing abnormal power on the 606..

i can measure the current on both units to compare, thats a good idea.

i bought an original boss aca-240 just now to test