Tapco 8201B schematic needed. This is an 8-ch mixing board, late 70s vintage.

[mdxeng]

Tapco 8201B schematic needed

[Enzo]

I don't have one scanned. What are you trying to repair on it?

HAve you contacted Loud Technologies and asked if they have these old legacy units documented?

[mdxeng]

Hello Enzo - yes, I asked Loud Tech and they responded that they didn't have this "legacy" schematic and I should try a certain source "tapcofixer" (partial email address) which so far didn't respond to my email.

This unit has an apparent issue with the power supply feed into the channel boards. Of the eight lines going to all the channel boards, I measure one feed at 6.5v and another at 5.6v and the other six lines are 0vdc. I suspect the two voltage feeds should be + and - something. So, signals don't hardly pass through from a channel input to the main outs. Me and the owner like this board since it has audio transformers on each preamp board which in my experience makes for a sweeter overall sound. If you have a schematic and can post I'd be grateful.

[Enzo]

Is the power supply board separate? Can it disconnect from the rest of the system? If so, do the voltages return to normal?

Did you mean 6.5v and -5.6v? Or were both positive?

[mdxeng]

Both voltages are positive (6.5v and 5.6v) which seems wrong. There's a main board with power supply and main controls and meter, etc., then each channel has its own board. The power supply is in the middle of the main board which makes it hard to reverse-engineer, so a schematic would be a big help.

I could try to remove the 8-conductor feed from the main board to all the channel boards, then measure the voltages to see what happens...

[Enzo]

When you have both polarity supplies, and the voltage on one is the wrong polarity, it often means the path from the corect polarity is open. Imagine you stretch a ruber band in front of your face. The two ends are on either side of your view. Now if one side is let go, the whole thing is pulled over to the other side. Kinda like that.

Look for the rectifiers and filters. Got both raw supplies? Then the regulators are either likely a pair of three-leggers, or they are discrete transistors. COnsidering the age, I migh bet on the latter. SO if ther is a three leg regulator or a pass transistor, is there good raw voltage on one side, but nothing out the other. Or even that reverse voltage knocking on its back door.

[oc disorder]

Although not the one you want there a few early EV schematics here.
They also have the owners manual of yours.

http://telexlegacy.com/archives/EV/M...ice%20Manuals/

http://telexlegacy.com/archives/EV/M...ers%20Manuals/

6000 Series Service Manual.pdf 2.5M
6200A & 6200B Service Manual.pd.pdf 2.8M
8108 Service Manual.pdf 1.8M
8200 & 8400 Series Service Manu.pdf 3.0M

[mdxeng]

Hey oc disorder; bingo. I believe this "6200A & 6200B Service Manual.pd.pdf" is pretty close to the 8201B. DRWG 24031 on page13 looks like it's the same or mostly the same as the 8201B. It's a help. Thanx.

Enzo - pretty sure you're on the right track. It's probably a power supply issue with a zener diode or a cap. Thanx.

[g1]

The actual service manual you need is the 6201 series. If the 6200 series is close enough, that's great!
Should you decide you want the exact manual for the long term, you can buy them online, printed or download:
Tapco High Quality Service Manuals User Owner Instruction Manuals Schematics Brochures Literature Printed PDF (some FREE)
Tapco Schematics

[mdxeng]

I believe your are right.

Anyone got a Tapco 6201 schematic? (the power supply in the 6200A/6200B is different than the one in the 8201B.

[Bill Moore]

I'll look this evening, when I get home, I thought I had schematics with the paperwork I got with my 8201B. If so, I'll get them scanned for you.
We used that board with an 8 ch expander back in the day.

[mdxeng]

The owners manual has a flow chart which I already have. I do hope you can find a schematic which would be a help.

[Bill Moore]

You're right, it's just a block flow chart. I got more paperwork when I bought the expander board, but I didn't find it, sorry.
Hope you get it repaired, we used ours for years, and other than scratchy pots, had no maintenance. I used the expander in larger venues to bring the instruments into the mix. (We had no soundman).

[mdxeng]

Thanks for looking, Bill Moore.
-MD

[Enzo]

We used to have a can of some sort of solvent - smelled like paint thinnner - and it was specifically for Tapco mixers. It seemed the grease or whatever lube was on the pot shafts would stiffen up to where you could barely turn the controls, and this stuff was what Tapco used to loosen or free them, so they turn more freely. The small can would last a lifetime, since it only took a drop or two per shaft, and of course only when needed. Had some real chemically sounding name, not a brand name.