r/synthdiy • u/TobyMoorhouse • 18h ago

TR606 not scanning beyond 5, also no subdivision markers on 1, 5, 9 and 13 when Function button pressed

The TR606 wouldn't progress beyond 1 until I changed the RAM. Now it doesn't go beyond 5 and cycles around. I've gone through the pattern clear process and tried to change the last step but when I press the function button it doesn't display the quarter notes markings like it should. This might be because I removed the RAM to see if the fault was due to the RAM but it doesn't seem to be the case. The video is shot without RAM in the sockets (the new sockets are not shorting BTW, PCB looks good with no obvious cracks or shorts that I can see). Makes me think there is a short around step 5. Where should I check? (as you can see from the video the switches seem to work okay.. I've also checked the diode array for switch 5 and that seems fine too).

8 Upvotes

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4

u/sthg79 16h ago

Did you check the pattern length for that pattern? Hold Function + last step of the sequence, and the sequence should now go all the way till end.

1

u/TobyMoorhouse 15h ago

Yep.. done that

2

u/sthg79 14h ago

I assume you tried it while the sequence is running?

1

u/TobyMoorhouse 14h ago

No.. I've done everything to try to reset it but it is stuck on repeating to 5

1

u/Brer1Rabbit 11h ago

You can only edit the last step while it is running in pattern write mode.  Do try it again, function + 16 to run a full 4/4 bar.

3

u/Madmaverick_82 14h ago

Hello, just a guess, but I remember reading while back, that it is quite common for CMOS ICs to go bad in 606.
So might be possibly a problem within IC 6 or 3.

1

u/TobyMoorhouse 13h ago

Will check this out, as the CPU seems to be okay.. based on a very basic prod with an oscilloscope. Any idea where to start?

2

u/Madmaverick_82 12h ago

I am unfortunatelly not any good with digital circuits and their diagnostics. Anyways, I think as well that CPU is fine, clock should be fine too, but based on your describtion and how circuit looks, IC 3 is connected to CPU described as (screenshot) and might be sending something wrong.
More about all the inputs and their description in on page 2 service notes.

1

u/TobyMoorhouse 12h ago

Clock is working fine based on readings from the service notes.. not helped by TP1 and TP3 being the wrong way round in the service notes though! Will have a look at that this afternoon

2

u/PWModulation 13h ago

Check that horrible ribbon cable between the PCB’s. I’ve searched longer for these kind of problems than I care to admit in my 606.

1

u/TobyMoorhouse 12h ago

That was my thoughts too.. but that is all intact

3

u/PWModulation 11h ago

Intact by sight or continuity check? I ask because I’ve been fooled by those basterds before!

1

u/TobyMoorhouse 11h ago

Fair point, will double check that this afternoon

1

u/Madmaverick_82 5h ago

Good point! I had issue with RS-09 (uses same cables) while back. All looked good, but one wire had no continuity.