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Author Topic: MP-1 Classic dead  (Read 4144 times)

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tangohf

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MP-1 Classic dead
« on: Time Format »

Dears, my name is Marco and wrote from Rome.

I recentrly bought a dead unit of this fantastic preamp with the ideea to make it work :metal: :metal:.
I red a lot around internet to learn as max as possible.
I checked voltages and they seems ok.
I saw that many documents speak about the crystal and the .047 cap (c136) in the reset but i can't find it in my unit, is it related to other mp-1 types?

Do you think i'd have to change the crystal?
Have you some suggestions?

Thanks a lot in advance!!
 :bow: :bow:   :wave:
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MarshallJMP

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Re: MP-1 Classic dead
« Reply #1 on: Time Format »

The classic uses a 8031 µcontroller and the MP-1 a Z80.Now the reset circuit for a 8031 is way more simple,just a cap and a resistor (C4 and R1).So what you can check first if the RST pin (pin9 of U9 (8031AH)) is low,if it's high it won't start because it's stuck in reset mode.Check also  if you have 5V between pin 20 and pin 40.
Then next is the oscillator for the clock which has to be 12MHz (between pin 18 and 19) but you need a scoope or a frequency meter for this.If you U6A (74hc08) is busted it won't start either because it can't acces the EPROM,but usually it does something,same deal with U8 (74HC373).

So first check 5V,the RST pin and the clock.Usually the problem is found here.
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rnolan

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Re: MP-1 Classic dead
« Reply #2 on: Time Format »

Hey tangohf, great advice from MJMP if you're up to the electrical stuff, otherwise, your in Rome, he's in Belgium, personally I'd send it to MJMP  :thumb-up:
Cheers R
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tangohf

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Re: MP-1 Classic dead
« Reply #3 on: Time Format »

Thanks a lot for your suggestions, MJMP.
Following you i checked around and the 8031 and i saw that pins from 1 to 8 has 180mv ca. from ground and pin 9 has 220mv ca. from ground.
Between pin 20 and 40 there are 4.80v ca.

Other, i made the battery mod, to make it changeable easy and changed C4 with 22uf (this i had..) and C1 with 10k (it was 5k originally).

After that i turn on the machine and a strange thing happened, it started with leds on from overdrive to effects loop and four strange digits on the display (something like G with missing elements).
After that no more life on it.

What do you think?

Also what rnolan says it's a good option, i'd like to do it by myself but i'm a little skilled only on tube. If i'll not be able to fix it, and you're agree, i can send it to you. In case we'll speak through personal messages.

Thank a lot to both.
Bye!
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MarshallJMP

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Re: MP-1 Classic dead
« Reply #4 on: Time Format »

Well send me an email,for me this is easier then PM.We'll see what we can do first before you ship it to me.
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