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Tr 606 Bass Drum problem

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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Fri Dec 04, 2020 11:22 pm

Thanks for the reply.
Just to get this clear I probed in ohms neg probe Q15 and pos probe q 18 and got 4.64 ohms
is that what you were asking me to check?
sorry for more clarification on my behalf...still very new to me.

thanks
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Re: Tr 606 Bass Drum problem

Postby Folderol » Fri Dec 04, 2020 11:39 pm

Yes. If that is accurate it is a real problem, so please check again and make absolutely sure you're on the right pins. Also, as a cross check, touch the probes together and make sure like that you get zero or very close to it.
To confirm what you should be seeing, please also check Q18 against Q29 in the same way and/or Q29 against Q27. These all should be connected to the same common trigger line.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Sat Dec 05, 2020 10:35 am

checked outer legs (can’t reach centre ones) of transistors Q18 - Q29
5.058 opposing legs 9.40 ohms

Q18 - Q27
9.40 opposing legs 4.650 or 0.2when switching over transistors
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Re: Tr 606 Bass Drum problem

Postby Folderol » Sat Dec 05, 2020 2:22 pm

Hmmm. This isn't right. Only the last figure is what I would expect. However, it seems I assumed you know more than you actually do. That's my error, not yours. Also I haven't explained what I'm trying to discover - and I usually do. So that two strikes!

Going back a bit, to that opamp. The reason I wanted those specific pins is that it is a pretty ordinary amp in a pretty standard circuit. Like this all three pins should be very close to the same voltage, and if either of the input pins was wrong the output would be wildly wrong. This checks the amp itself as well as the DC conditions it's fed with. Also being actually on the pins proves it really is connected. Finally if all three pins were exactly the same I might suspect a short circuit chip - but that's extremely rare.
I didn't bother with the second section of the amp. because if just one section was wrong you'd still get something - it just wouldn't be right.

Moving on, I'm now trying to establish the triggering conditions. There is a common line - helpfully marked Trig on the PDF version of the drawing, and the Bass then has its own separate line. The trigger is what actually fires all the sounds, and the individual lines act as a switch to enable them.

The fact that only the bass drum is not working means that the trigger must be being generated, but we don't know if it's reaching the bass circuit. Unfortunately you can't make assumptions about the transistor legs unless you know the specific device. Most follow the pattern e,b,c looking from underneath but some are b,e,c and most of the bigger ones are b,c,e - not terribly helpful!

The specific points I want to check are the leg of Q15 that should go directly to one leg of R62 and the leg of Q18 that should go to one leg of R97. All of these should be connected together and measure pretty close to zero.

The same is true of the leg of Q29 that goes to one leg of R127 and also the common point as above.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Sat Dec 05, 2020 9:46 pm

Not at all and I really appreciate your help with this. Just wish I new more so I new what to look for.

Q 15
measure in dc switched on but not running and with negative on the chasis. Is that correct?

DC on but not running
leg 1 (0.0001)
middle leg 2 (0.002)
leg 3 (0.002)

ohms power off

leg 1 4.272
leg 2 11.03
leg 3 9.00

Q 18

DC on but not running
leg 1 0.001
leg 2 0.001
leg 3 0.001

ohms power off
Leg 1 4.273
leg 2 11.01
leg 3 8.92

Q 29

DC

leg 1 0.000
leg 2 - 0.004
leg 3 0.002

ohms
leg 1 4.271
leg 2 1.607
leg 3 9.02


r 62 ohms each end pos probe
9.00
4.273

r 97 ohms each end pos probe
11.00
111.8


R 127 ohms each end with pos probe
9.02
4.270

Let me know what else you need.

Thanks again, really appreciate it
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Re: Tr 606 Bass Drum problem

Postby Folderol » Sat Dec 05, 2020 10:48 pm

I'm afraid this still isn't what I'm trying to find out.

I'm not concerned about DC conditions at the moment, just looking for continuity. So I want you to use the meter find just exactly which leg of Q15 is the emitter. This leg should connect to R62 but not R67. So probably the best starting point would be to put one probe on one end of R62 (not to ground or anywhere else), and the other probe on one end of R67. Swap them until you find the combination that gives zero (or very close to it). If there isn't one then that in itself is a fault.

This sounds odd, but it is the point you dont want to use. Instead use the other end of R62 to find which transistor leg is the emitter - it should again be virtually zero.

Now put one probe on that known point and the other probe on each of the legs of Q18. Just one of them should again read close to zero. If none do, that is the fault we are looking for. If one does read zero that line is OK and we move on.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Sun Dec 06, 2020 10:06 pm

Sorry for the late resonse, was out all day today.
Thanks so much with your patience.
I Think I found Q15 emitter measuring zero running against R62 and R67 as suggested
i then measured Q18 against Q15 - Hope this is what you asked

Each leg was measuring different values
9.38
4.725
20.02
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Re: Tr 606 Bass Drum problem

Postby Folderol » Mon Dec 07, 2020 10:02 am

Unfortunately, this is still not what I'm looking for. If I understand right, you ended up using the common point between R62, R67 and Q15. That is actually the base of the transistor. You want the other end or R62. This should then connect to one leg of Q15, and that is the emitter.

Also something as occurred to me. You meter is almost certainly an auto-ranging one, and the figures you are getting look quite wrong. I suspect that it is not ohms you are reading but k or even M ohms. This would be identified by a small k or M alongside the reading, and would make much more sense.

With that all in mind, can you try again.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Mon Dec 07, 2020 11:49 am

:headbang: god I am sorry yes you are tight there is a M next to the Ohms. What should I be measuring in?
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Re: Tr 606 Bass Drum problem

Postby Folderol » Mon Dec 07, 2020 12:24 pm

OK. That makes sense now.

I've just though of a simpler test you can try. Using the meter as before, see if any leg of Q15 reads near zero to any leg of Q18. If so, those are the emitters of those transistors and they are correctly connected together.

If none do, try the same check with Q18 and Q29 just to make sure we have it right.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Mon Dec 07, 2020 9:15 pm

Just to clarify, Am I testing pos probe q15 legs against q18 legs in Ohms vice versa?
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Re: Tr 606 Bass Drum problem

Postby Folderol » Mon Dec 07, 2020 9:30 pm

Lionel Red wrote:Just to clarify, Am I testing pos probe q15 legs against q18 legs in Ohms vice versa?
For this test, on ohms, yes, but it doesn't matter which way round you have the probes, as long as you take one leg of Q15, and try it against all legs of Q18, to try to find the zero reading one. If it's not there, move to the next Q15 leg and try again until you've either found the link, or you've tested all of them and none of them respond.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Mon Dec 07, 2020 9:55 pm

I went through q15 against q18
then q18 against q29
one of all three legs read 0.1
The others were all O.L

Is that helpful?
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Re: Tr 606 Bass Drum problem

Postby Folderol » Mon Dec 07, 2020 10:41 pm

Lionel Red wrote:I went through q15 against q18
then q18 against q29
one of all three legs read 0.1
The others were all O.L

Is that helpful?
That's exactly what I wanted to know. Is that for just one pair of transistors, or for both? If it's just one, it suggests there is a break in the trackwork. If it's both then it proves that the bass drum is getting the trigger signal.

If you get that 0.1 on both we move on to checking the switch for that drum.
Finding out if it is getting the individual switch line from the BD label will be a bit more complicated. However there is a way we can fake it.

To do this you have to have the unit running a pattern then short the collector Q14 to ground. You should then get a continuous stream of bass drum hits, along with the others. The collector is the leg that goes to R67. Be absolutely sure you are on the right point, otherwise you could possibly damage something.

If you do get this, then the fault is further back in the logic. If you don't, the fault is probably between IC5 and the output.
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Re: Tr 606 Bass Drum problem

Postby Lionel Red » Mon Dec 07, 2020 11:58 pm

Yay! finally and thank you.
I believe it was the same on both Q15 to Q18 then Q18 - Q29.
Not quite sure I understand the next bit sorry.
How does one short the collector...with the probe and if so which one?
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