Aquaboy MN3205 - No delay :(

[eldanko]

Howdy friends -

Finally got around to building up an old Aquaboy board.  I'm getting clean signal through, but no delays.  Clock is making noise.  Getting clean signal on pin7 of the MN3205 as well as at the compander, but no delay anywhere.  Haven't taken voltages yet - based on everything so far, would you guys guess that a bad MN3205 might be the culprit?

FWIW, I'm currently using a v571 compander with no parts substitutions.

Here's a quick and dirty cell phone shot of the chip in question:

[madbean]

Take some voltage readings on the BBD and clock and I may be able to suggest something.

Have you tried the MN3205 in any other circuit? The indent and lettering look a little suspicious to me, but it's hard to say.

[gtr2]

I'd agree.  That mn3205 looks a little fishy. 

[Scruffie]

I've seen them like that, it's an early mold.

[eldanko]

Thanks for the replies, friends.  Sadly, I do not have another MN3205 circuit to test with, nor do I have any more chips.  My Dirtbags are both MN3005.

Input voltage: 9.4

Here's the voltages I'm getting on the 3205:

1: 0
2: 3.4
3: 2.5
4: 2.5
5: 7.5
6: 3.4
7: 3.8
8: 0.4

And here's the 3101:

1: 6.9
2: 3.4
3: 0
4: 3.4
5: 3.4
6: 3.3
7: 3.3
8: 0.4

[madbean]

Okay, try this instead: remove D2 from the PCB and put a jumper in its place. Now put D2 (or another 1n914 or 4148) between pin1 and pin8 of IC4 on the bottom of the PCB as illustrated below in orange. This will set the Clock at the same voltage as the BBD and change the Vgg voltage to about 14/15 of the Vd supply.

If that doesn't work, it may be a bum BBD.