r 151 accent resistor burns

[franzkleid]

r151 esistor starts burning after powering on !
checked all 20 times !
Somebody any other sugestions

[gihaume]

As stated in the thread VCA accent troubles, we are 2 people to have this same problem, and at least me without any other unfindable mistake (yes only another one but I know why).

I also checked many times a lot of things, so much that with all the movements, I broke the "Cable 10Pos" linking both PCBs! I checked every component's place and way, resistors values, and transistor's proper functioning of the accent section.

[e-licktronic]

Dear Diyer,

R151 burned because you get a short cut between ground and +15v psu rail.
C34, Q27 or the 4011 could be the problem.

Best regards,
e-licktronic

[keen]

Hello franzkleid,

I had same problem on 4th batch kit.
Please try unbuffered 4011UB.
I solved R151 problem by it.

cheers

[gihaume]

Thank you!

The batch before the 4th did have a different 4011 than BE?

[zmb]

Hello franzkleid,

I had same problem on 4th batch kit.
Please try unbuffered 4011UB.
I solved R151 problem by it.

cheers

wow is that really the issue? My local electronics retailers don't seem to differentiate, just listing "4011" without any suffix. I guess I could go in-person or call to verify the buffered vs unbuffered versions...

EDIT: I just checked the TR-808 service manual and as far as I can tell they used 4011B type NAND gates. So maybe that's not the problem?
Attached screenshot from the service manual:

Untitled.jpg (21.15 KiB) Viewed 5131 times

[keen]

Hello.

Sorry, I'm not sure why UB version solved it.
I have 2 kits of 4th batch. Both kits had same problem. And solved it with 4011UB.
BTW, 4011UB is used for 9090 too.

regards,

[krisbo]

Replace your 4011. I replaced mine with a 4011BE and it's rocking now!

[gihaume]

I also have a few yocto kits so I tried with the 4011BE of another kit (not built yet), and again the same problem!

[krisbo]

By the sound of it there may be some issues with the 4011 used seeing as a fewguys have had issues with them. Pick yourself up a new one from an electronics shop and see how you go.