No lights No sound and a hot ic

[t-rack]

just like the title says u13 is burning hot after a couple seconds and no lights unless i start pulling out KH then they flicker. tested VR1,2,3,4 all OK. any ideas are greatly appreciated.

[rnolan]

Hey t-rack MP1/2 ??

[MarshallJMP]

"pulling out KH" ? what do you mean by that?

What happends if you pull U13 out ?

[t-rack]

it's an MP-1 . and i believe KH is what the ribbon cable is labelled in the layout.

[MarshallJMP]

Ah okay KH,the grey ribbon cable right?Now if you pull it out it won't start up because the midi board gives out interupt signals to the Z80 processor.Have tried pulling U13?

[t-rack]

yes pulled u13, now u14 is hot and still no lights. like something is drawing too much current through the chips, but what?

[MarshallJMP]

Are you sure your voltages are okay?measure between pin 1 and pin 7,there you should have -15V and between pin 7 and pin 16 you should have +15V.Try to pull them both out and see if it starts.

[t-rack]

yes between 1 & 7 is -15v between 7&16 is 14.8v

[t-rack]

Ok now i feel stupid, i am just noticing that U13,14 are the wrong IC"s . found this out comparing it to a working mp-1 i have here. correct ones are now in place but still no lights/sound except for a little flickering when i turn it on after a while. and just so you know i bought it used from someone who was "from what it looks like" trying to do the factory updates such as changing the diodes putting the jumper on U29 ect.

[rnolan]

Hey t-rack, then would seem to be either something damaged with wrong chips (let MJMP know what they are hopefully he will know if that is/was a possibility) or, to me more likely (based partly on my Mate MikeBs recent experiences with the noise mod, broke a track, fiddly, suits those who do it regularly LOL), there are some issues with the previous owners attempted changes ?  Mmm diodes, they tend to stop things if they're not right. May just need a re-flow/check around those components ? Anyway, hope it's that simple.

[MarshallJMP]

Has pin 17 of U29 (Z80) 5V?

[t-rack]

no only  1.8v

[MarshallJMP]

This has to be 5V,this the NMI (non maskable interupt) input which has to be high (5V) else it will execute an interupt.So check the jumper to the 5V.
Also check R251 and check if they did the update correctly.

[t-rack]

U25 has jumper from pin 17 to 24 and trace cuton pin 17. r251 removed 3.3k between u40 pin 11 u44 pin12

[t-rack]

and still only 1.5vdc on pin 17