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Author Topic: Teisco CheckMate 22 schematic  (Read 288 times)

galaxiex

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Teisco CheckMate 22 schematic
« on: March 22, 2020, 12:56:07 PM »
Got this off the bay awhile back, just getting to it now.

Seller pics.

The seller said the reverb does not work and I found the tank output coil to be broken.
No surprise, considering the amount of corrosion in there...  ::)

The schematic inside the back panel is "not quite" correct.

I traced the board and drew a correct schematic. (next post) 

 :)

« Last Edit: March 22, 2020, 01:17:54 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #1 on: March 22, 2020, 12:58:50 PM »
Here's the corrected schematic...

Edit; added main voltage to schematic

« Last Edit: March 29, 2020, 12:21:31 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #2 on: March 22, 2020, 01:02:05 PM »
Here's the badly corroded output coil.

I have already managed to get the coil bobbin removed from the core.

I have a pickup winder so I'll make an attempt to rewind the coil.
« Last Edit: March 22, 2020, 01:03:28 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #3 on: March 22, 2020, 01:11:23 PM »
Here's some mods so far....

3 wire power cord and a fuse!!!  :o
Also got rid of the "death cap", C20 in the original schematic.

C1 and C7 changed to 100nF, altho C7 is not doing much right now as the reverb tank is still out.

Removed the aux speaker jack and put the fuse holder in that hole.

More mods to come....

Input impedance is dismal, so a buffer on the input is in the plan.
Possibly a (slightly) bigger power Tx and full wave bridge rectifier.
« Last Edit: March 22, 2020, 01:17:17 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #4 on: March 22, 2020, 02:35:04 PM »
BTW, they made these (CM-22) in different versions.

Here's the other type, I call it the "square head".

Not mine, internet pic...

It only has Tremolo speed, no depth control, and has foot switch jacks.

If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #5 on: March 28, 2020, 03:52:23 PM »
Here's a layout for the original board.

If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #6 on: March 29, 2020, 12:16:14 PM »
Here's some modifications to the little CM-22.  :)

Pics show the added stuff.

The input buffer is just hung on some stiff wires, right on the input jack.

The added C24 and R39 (see schematic) give a large gain boost,
very "crunchy" germanium transistor distortion, almost Fuzz Face territory.  8)

I tried with just the 100uF cap and it was too much gain, squealing feedback.
The 1K resistor tames it just right.
Thinking to maybe put the C24, R39 "gain boost" on a switch...

Last pic is a size comparison of the power Tx.
The bridge rectifier setup is temporary, I'll make a little board for it.

Can you tell I'm bored with being stuck at home?  ;)

Edit; still haven't fixed the reverb tank, I'll get to that later today... maybe...


« Last Edit: March 29, 2020, 05:35:02 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #7 on: March 29, 2020, 03:27:00 PM »
Ok, the reverb coil winding has started....  :)

First pic is the bobbin mounted to the winder with the old wire still on it.

Second pic is the new wind started.

Wow this thing is tiny!

Winding going really sloooow cuz I don't want to break the wire and hafta start over...

The new wire is thicker than the old, so I'll over-wind it somewhat.

Old wire measures .015"
New is .025"

I was able to find the end wrap and paid attention to the direction of wind.

New wind is going on the same direction, don't know if it would matter (phase issue, maybe?).


« Last Edit: March 29, 2020, 03:32:22 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.

galaxiex

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Re: Teisco CheckMate 22 schematic
« Reply #8 on: March 29, 2020, 05:40:02 PM »
Got the coil wound and installed.  :)

4760 turns and 662 ohms.

It's alive!
We have reverb!
(albeit not very good reverb, but I expected that  ::))

Now I'll disassemble the tank and clean it up some,
just to get rid of some of the corrosion.

Edit: This is the output coil that I just wound at 662 ohms.
No idea what it was originally, or what it's supposed to be.
Seems to be working fine.

The input coil measures 1K6 ohms DCR and both coils were/are wrapped with blue tape.
I don't know if the tape color indicates coil impedance/DC resistance like the Accutronics tanks.
« Last Edit: March 30, 2020, 08:12:07 PM by galaxiex »
If it ain’t broke I’ll fix it until it is.