New here...

To cut down on spam, we tend to remove users that haven't posted anything after a day or so, so this is the place to say hi for the first time.
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retroman
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Joined: Mon May 08, 2023 10:01 pm

#1 New here...

Post by retroman »

Hello!

I was directed here about a problem with chip ID on an SP10 and liked it, so here I am. Been in audio all my life - Grundig TK8 started the rot, and it's still getting worse! Recording, mastering, remastering, designing and fixing kit. Probably a lurker by nature, but I'll pipe up if I can help.
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Nick
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Location: West Yorkshire

#2 Re: New here...

Post by Nick »

Hi, what was the sp10 issue (out of interest)
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
retroman
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Posts: 2
Joined: Mon May 08, 2023 10:01 pm

#3 Re: New here...

Post by retroman »

Well, it still is, as the chip hasn't arrived, but the thing doesn't respond to the start button. The troubleshooting guide in the manual led me to IC8, a J-K flip-flop which was doing neither. As all the logic ICs have obscure Japanese codes, I had to do some digging to identify an equivalent. I went on another forum to check my results and got steered here, where somebody has already trodden the same path. With any luck, that's the only chip that has gone...
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Nick
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#4 Re: New here...

Post by Nick »

OK, I will have to remind myself, but when I had to rechip a sp10 I found there was was error around the switch logic. I vaguely remember the problem was it used open collector gates. And the open collector makes sense in the case of three of the gates, but the fourth was used as a normal nand gate, but had no pull-up resistor on the output so while it worked in the original chips, the latter replacement was failing.

The other thing I found was the switching on some of the gates worked again with the original parts, but later ones needed more current on the input to make it switch properly. If I remember the problem was the low current on the input was fine until the device switched and when that happened the input went up again briefly before clocking again so the flip flop was clocking twice so looked like it wasn't switching at all.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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Nick
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Posts: 15813
Joined: Sun May 06, 2007 10:20 am
Location: West Yorkshire

#5 Re: New here...

Post by Nick »

Just checked, the open collector problem was IC12, pin 8 which fed IC4 was the missing pull-up.

IC8, try changing R221 from 47k to 4k7

I think R261 and R264 also worked better with 4k7 for the same reason.
Whenever an honest man discovers that he's mistaken, he will either cease to be mistaken or he will cease to be honest.
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