Author Topic: Sunn Beta Lead repair questions  (Read 685 times)

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Offline Just_another_Beta_guy

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Sunn Beta Lead repair questions
« on: March 31, 2021, 09:21:33 pm »
Hello, this is my first time on this site, I would like to ask where I can get the 103 and 106 IC Chips for my beta lead's pre-amp. I bought this beta lead knowing it needs some repairs, but the previous owner didn't disclose the extent of how much work needs to be done.. I recently picked it up from my repair guy, and he says the pre-amp section is pretty bad. More than one knob has been replaced, the inputs have been messed with before with shoddy soldering, and both the 103 and 106 chips are missing. The technician was able to get the amp to hold a full load, but hasn't been able to get any sound to come through, which I assume is due to a bad ground on the input and missing chips. I'm no professional, but I can read a diagram and solder. I'll be running through all the caps to see if any popped or have a bad grounding. Any help would be greatly appreciated, thanks!

Offline loudthud

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Re: Sunn Beta Lead repair questions
« Reply #1 on: April 01, 2021, 12:20:31 am »
IC103 is just a 74C04 or a CD4069. These must be the old CMOS chips that will run on 15V. IC106 is an old Motorola oddball, the  MC14506. Again it's an old CMOS chip that will run on 15V. You might be able to find one, or you will have to build a little plug-in replacement that you will find here:

https://forum.sunnstillshines.online/index.php?topic=6864.msg29374#msg29374

You can find the parts you need here: https://www.jameco.com/

Get some flux cleaner or isopropyl alcohol and clean up that board. There are many small radial lead electrolytic non-polar caps on the board. Most are 1uF or 2.2uF. It is wise to just replace them all while you have the board out to work on it. Attached is the Beta service manual.

Keywords: Beta schematic service manual


 

Offline Just_another_Beta_guy

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Re: Sunn Beta Lead repair questions
« Reply #2 on: April 01, 2021, 01:58:10 pm »
I might have found a 14506 bcp chip, do you know the exact model number? There seems to be more than one variant of the 14506 chip.

Offline loudthud

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Re: Sunn Beta Lead repair questions
« Reply #3 on: April 01, 2021, 06:44:45 pm »
In the Service Manual posted above it specifies MC 14506 BCP. MC1 is a prefix Motorola used, the BCP suffix is almost always a package and/or a temperature range specification. Some other prefixes are: CD = National or RCA, HD = Harris, MM = Teledyne, TP = Texas Instruments, F3 = Fairchild, and there are a few other players.

Beware that there may be fakes available on ebay.

Offline Just_another_Beta_guy

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Re: Sunn Beta Lead repair questions
« Reply #4 on: April 01, 2021, 06:57:46 pm »
In the Service Manual posted above it specifies MC 14506 BCP. MC1 is a prefix Motorola used, the BCP suffix is almost always a package and/or a temperature range specification. Some other prefixes are: CD = National or RCA, HD = Harris, MM = Teledyne, TP = Texas Instruments, F3 = Fairchild, and there are a few other players.

Beware that there may be fakes available on ebay.

Thanks for the specifications, I better do a little more studying on this system before I remove the board.. How would I be able tell a fake one from the real deal?

Offline loudthud

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Re: Sunn Beta Lead repair questions
« Reply #5 on: April 01, 2021, 07:18:08 pm »
It can be pretty hard to tell the difference by just visual inspection. Usually the font of the printing on the chip is wrong, but you don't have a real part to compare to. Sometimes the date code may be wrong. The MC14506 hasn't been made in the last 30 or 40 years so that would be a clue. The biggest clue is that the parts just don't work electrically. Could be just the wrong part internally or nothing at all inside. The last time I went looking for these parts you could find people selling 50 or 100, but not one or two. Probably surplus inventory from some failed company.

Offline Just_another_Beta_guy

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Re: Sunn Beta Lead repair questions
« Reply #6 on: April 01, 2021, 07:52:35 pm »
I did forget to mention an important part of this deal...
The previous owner threw these chips in, forgive my ignorance lol.

Offline Just_another_Beta_guy

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Re: Sunn Beta Lead repair questions
« Reply #7 on: April 01, 2021, 09:28:20 pm »
Any who, thank you loud for providing the info I need to get started on this repair.