ADA Depot - A Forum To Support Users of ADA Amplification Gear

Let's Get Technical => Troubleshooting Problems => Topic started by: andtimebegins on November 30, 2020, 11:17:42 PM

Title: MP-1 no display or LED's
Post by: andtimebegins on November 30, 2020, 11:17:42 PM
I recently got an MP-1 (rev B,  1.38 eprom)  which is not working from a friend who pointed me in this direction for help.

The screen flashes on for about a second when I power on. LED's cycle on as well, but completely dissappear after about a second.

Wall voltage: 118v

1. C131 reads 11.9 volts with tubes in, with tubes out 13.2v.
2. Pins 11, 17,  24 and 25 of u29 reads 5.1v with tubes in or out.
3. Pin 16 of u29 reads 3.2v with tubes in or out.
4. Pin 6 of u29 reads 0.65v with tubes in or out
5. Pin 27 and 28 of the u30 reads 5.1v with or without tubes
6. VR4 reads 5.1v

I'm not sure how to test for pulses on pin 16 of u29. Its voltage is consistent with or without tubes.

I swapped out D38 and 39 with new ones.
Swapped out c136 for a new .047 cap.

No changes...

I'm starting to think it could possibly be the crystal? I have a new one on order(hope it's the right one, 12MHz). Should be here in a few days.

I'm wondering if these readings stand out as anything obvious? I don't own an oscilloscope.. but if need be, I could pick one up.

Thank you in advance for any help on this.

Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 01, 2020, 03:05:32 PM
So, I got the new crystal installed... still no go. Same results as with the old crystal.

hmmm....
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 01, 2020, 09:44:09 PM
Figured I'd drop a picture of the power section.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 02, 2020, 02:39:58 AM
Hi!

The unit seems to have the battery mod...
Has it any other mod inside?

It could be a problem related to failing Z80 CPU or EPROM, maybe.
Such failures can originate issues like that (I had a similar experience with another preamp, where the CPU broke and I had to change it: once the job was done, the unit came back 100% healthy).

You definitely need the help of MJMP.
Let's wait for him.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 02, 2020, 12:12:32 PM
So the leds in the buttons go on from left to right (one by one)?

If so then the display should show 8 from left to right, and then in your case 1.38, this does not happen?

BTW if you could get a scope that would be great -, this way we can troubleshoot it better.

Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 02, 2020, 02:27:16 PM
Thanks for the replies guys....

When I turn it on I do see an 8 sometimes real quick then it fades away to nothing on the screen.. Half of the push button LED's flash on and off, and then the other half does the same, all happens in about a second.  I think I've seen it also say ADA and I've seen it flash the 1.38. Maybe even looked like it was doing a count down or something?

I'm going to see if I can grab a scope asap.

Is there any chance though that it could be one of the IC's? Maybe the eprom? I'm not getting anything on pin 26 of the eprom. I've noticed you mentioned to others that you should get a reading on pin 26 and 28. I get a reading on pin 27 and 28. Is that normal?
 
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 03, 2020, 10:07:46 AM
Can you make a video of the startup and mail it to me so I can have a look?

BTW you are correct , it should flash one half of the leds then the other half, (mistaked it with the mp-2 which turns on one at a time).

It seems it wants to startup but something happends to prevent it, usually this is a power supply problem. Try to start it without the tubes.(just remove them).

Don't think it's a Z80 or eprom problem.

BTW does it restart or does it starts up and then a blanc display?
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 03, 2020, 02:01:10 PM
MarshallJMP. I'll do that asap!

I just got a 2 channel 20 MHz scope, its a bit old, but works good.

Oh the screen goes completely blank, to answer your question.

I really appreciate the help!
Title: Re: MP-1 no display or LED's
Post by: rnolan on December 03, 2020, 11:10:16 PM
Also check that the ribbon cable between display and PCB is seated properly in the PCB socket, I suspect MJMP is right and it may be power supply related but sometimes they can play up when the cable isn't connecting properly.  If you remove the EPROM and put it back it will force a full boot check where it runs through a series of self diagnostics (Maybe even looked like it was doing a count down or something) this maybe what you saw happening.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 04, 2020, 08:19:16 AM
I think maybe he saw the C 1 to 128 count up? andtimebegins, could it be it was counting up?

Ok you got a scope, nice  :thumb-up:, begin with the clock input on the Z80, should be 6 Mhz ( a period of 0.166µs )
Then on the interupt input you should see pulses.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 04, 2020, 01:36:32 PM
So this is what I got for the clock input.

I admit, I'm not too savvy with the Oscilloscope.

To be honest, I'm not sure I did this correctly.

Any chance you could tell me how to set this scope to read the interupt signal for pin 16?
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 04, 2020, 02:00:12 PM
Just put the timebase knob on 0.5 ms, the rest can stay like it is.

The clock period looks good as far as I can see, you have around 0.8 x 0.2 µs which is 0.160 µs, close enough.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 04, 2020, 02:26:13 PM
So I got this.

Its moving from left to right across the screen. Should I send you a video over of that? Or can you tell from this picture? Its a little blurry.

*dunno why the pic is coming in upside down? Haha
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 05, 2020, 12:07:00 AM
Ok looks good. Next I would check the CS lines of the eprom (pin 20) and RAM (pin 20).
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 05, 2020, 09:43:46 AM
Eprom (pin 20) = 1.7v with or without tubes.

RAM (pin 20)  = 4.64v with or without tubes.



Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 05, 2020, 12:58:35 PM
I mean measure it with the scope  ;D
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 05, 2020, 03:24:02 PM
Oh. Whoops! Apologies. Haha.

Do I measure these with the same settings on the scope you had me do the last test with?

Not sure if this is correct? I just took this pic:
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 05, 2020, 11:37:18 PM
Is this the eprom or the ram?

also set the voltage knob on 0.2 so I have a bigger image on the scope.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 12:43:14 AM
First pic is the eprom

Second pic is the RAM.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 06, 2020, 03:41:45 AM
RAM CS is not ok, should look a bit like the eprom.

Check U44 (74LS20)
pin 9 ==> should be pulsing
pin 10 ==> should be high (5V)
pin 12 ==> should be high (5V)
pin 13 ==> should be pulsing
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 09:32:51 AM
First pic is pin 9 of u44
Second is pin 13 of u44

Neither seemed to pulse like pin 16 of the z80 did.

Both pin 10 and 12 were 5.1v
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 06, 2020, 12:07:01 PM
Ok signals are there, looks like the 74HC20 is busted. On pin 8 you should have a signal like this. (see attachment)
My scope's timebase was set to 1µs. Check it and post a pic of it.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 12:24:24 PM
This is what I got on pin 8 of the u44
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 12:29:53 PM
So I tested it again.. now it does this everytime I test it.

Hmm...
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 12:48:34 PM
So, I've noticed that there is something up with that pin 8 of the U44. When I power the unit on again after waiting, I'm getting what I saw in the first picture, then it fades into what I show on the second picture.

Definitely seems like there is an issue there or something.

Just to be sure, I attached a picture of the chip we are talking about.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 06, 2020, 01:11:32 PM
Eating my popcorn while reading.
I bet there will be another working MP-1 in short times here.  :thumb-up:
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 06, 2020, 01:16:33 PM
Yep I think so too, I'm almost 100% sure that this is your problem. I would try to replace it. You need a 74HC20 not a 74LS20 like I mentioned before. They used an 74HC (CMOS) because the power consumption in static mode is far less than a 74LS (TTL) (up to a 1000 times). This 74HC20 is permanently under power,even when the MP-1 is powered down, that's why it's connected to the battery (the reason why they used a CMOS version). So make sure you use a 74HC20 !! or your battery will drain a lot faster.

So the RAM is only selected (pin 8 ) when pin 9 (Memory request) and pin 13 (Address 14) is high.

See attachment. Logic analyser pin 8,9,13 , yellow is actual pin 8 signal.

When pin 9 and 13 is high pin 8 is low. (RAM Chip Select is active low).

Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 06, 2020, 01:25:44 PM
Yes that's the one, I see it's in a socket so easy to replace. Just desolder the resistor, replace it and resolder the resistor. (without the resistor it won't boot)

These fail sometimes and yes some MP-1's came with these in a socket.

So it seems it works for a few seconds and then the Z80 crashes due to the bad CS of the RAM. That's why the leds work for a few seconds.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 06, 2020, 02:02:10 PM
So it seems it works for a few seconds and then the Z80 crashes due to the bad CS of the RAM. That's why the leds work for a few seconds.

So, basically, the Z80 is failing/crashing not because it's broken but because of a busted chip related to RAM access?
Lucky guy: the broken chip is socket mounted.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 06, 2020, 02:11:03 PM
Yes, it's trying to read from RAM and it gets garbage in and crashes.

I've seen these fail before that's why I wanted to see the signals because I was already pretty sure this was the problem.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 06, 2020, 02:22:43 PM
Yes, it's trying to read from RAM and it gets garbage in and crashes.

I've seen these fail before that's why I wanted to see the signals because I was already pretty sure this was the problem.

I won the bet.  :lol:
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 06, 2020, 02:24:53 PM
 :thumb-up:  :whoohoo!:
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 06, 2020, 02:31:29 PM
An issue with a cheap solution!
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 02:58:53 PM
Thank you so much MarshallJMP!!!

Is this the correct part to order?

The only number thats different is the "549". On the original part it says "741". Will that make a difference?
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 03:31:26 PM
Actually, found these for .39 cents.

Just want to be sure before I buy:

 https://www.jameco.com/shop/ProductDisplay?catalogId=10001&langId=-1&storeId=10001&productId=45583    (https://www.jameco.com/shop/ProductDisplay?catalogId=10001&langId=-1&storeId=10001&productId=45583)
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 06, 2020, 03:40:34 PM
I think this one would be good as well:

https://www.mouser.it/ProductDetail/Texas-Instruments/CD74HC20E?qs=xFfolx0DHx3Po1GpIhjG1w%3D%3D

Or:

https://www.ebay.com/itm/CD74HC20E-SN74HC20N-DUAL-4-INPUT-NAND-GATE-74HC20-IC-1-pcs/133272187753?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225086%26meid%3Dd0694875b7534d95a3b0034ee007b987%26pid%3D100623%26rk%3D1%26rkt%3D5%26sd%3D174142942335%26itm%3D133272187753%26pmt%3D0%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic%26brand%3DRCA&_trksid=p2047675.c100623.m-1
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 06, 2020, 04:02:50 PM
I think this one would be good as well:

https://www.mouser.it/ProductDetail/Texas-Instruments/CD74HC20E?qs=xFfolx0DHx3Po1GpIhjG1w%3D%3D

Or:

https://www.ebay.com/itm/CD74HC20E-SN74HC20N-DUAL-4-INPUT-NAND-GATE-74HC20-IC-1-pcs/133272187753?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225086%26meid%3Dd0694875b7534d95a3b0034ee007b987%26pid%3D100623%26rk%3D1%26rkt%3D5%26sd%3D174142942335%26itm%3D133272187753%26pmt%3D0%26noa%3D1%26pg%3D2047675%26algv%3DDefaultOrganic%26brand%3DRCA&_trksid=p2047675.c100623.m-1

Thanks dude!:I'm gonna get it ordered asap and will report back my results!

Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 06, 2020, 04:24:06 PM

Thanks dude!:I'm gonna get it ordered asap and will report back my results!

GO!!!!!  :thumb-up:
Revive that unit and make it scream again as it deserves.
An ADA MP1 has no equal.
Title: Re: MP-1 no display or LED's
Post by: rnolan on December 07, 2020, 01:45:46 AM
An ADA MP1 has no equal.No but it has a better (MP-2  >:D ) LoL...
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 07, 2020, 03:56:15 AM
I guess you made your order by now, so let us know the results.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 07, 2020, 01:09:33 PM
An ADA MP1 has no equal.No but it has a better (MP-2  >:D ) LoL...

Pfffff....WHO came first???  :lol: :lol: :lol:

 :banana-upsidedown: :banana-upsidedown: :banana-upsidedown: :banana: :banana: :banana:
Title: Re: MP-1 no display or LED's
Post by: rnolan on December 08, 2020, 12:00:29 AM
(Pfffff....WHO came first???) Too true my friend and it was a really good prototype  :lol: .  That's a bit unfair though, the MP-1 totally changed my world, I've hardly used my '73 Marshall 50 since I bought my first MP-1 which I loved dearly and used for many years.  When MP-2 came I bought one as soon as I could, I love the extra features, they do sound quite different though.  One of my MP-1s seems to have similar issues to andtimebegins, hopefully my tech can read this post and it will help get it sorted.  My other MP-1 works but has midi issues changing programs  :facepalm: .  I must say when I first got them both and tried them out, albeit quite quickly, I had a good measure of nostalgia and wanted access to those tones again.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 08, 2020, 07:41:52 AM
(Pfffff....WHO came first???) Too true my friend and it was a really good prototype  :lol:

ADA did great stuff in the '80s and '90s.
Starting from the original MP1, through the Classic and MP2.
That's just a matter of taste.

I personally prefer the direct, raw tone of the original MP1...but you've to know it was the very first tube MIDI preamp I could afford (used from a friend) when I was 20.
I forgot those stuff for decades, and when I started back to collect rack stuff....the ADA MP1 has been like coming back home.
I know, I'm not very objective...  :lol: :lol: :lol:

I really want our friend andtimebegins to have his MP1 alive again.
About yours...you could suggest the same fix to your tech. Why not? Easy and not expensive. No risk.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 09, 2020, 08:51:46 PM
Well, bad news guys.... it didn't work.

I ordered 2 of the same chip. Both with the same results as before.

MarshallJMP would there be something else I could try? I appreciate your help so far, I feel like we are very close to getting this fixed.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 10, 2020, 11:27:39 AM
Oh that's to bad, put in the new ic and do the measurement again, see if the results are the same on the scope.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on December 11, 2020, 03:14:41 AM
Well, bad news guys.... it didn't work.

I ordered 2 of the same chip. Both with the same results as before.



NNNOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!  :dunno: :dunno: :dunno:
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 11, 2020, 10:27:06 AM
Could be that it's either the device before the nand gate or the RAM (although I doubt that).
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 11, 2020, 12:32:33 PM
First pic is pin 8 of u44 with new chip
Second pic pin 13 of u44 with new chip

Pin 8 seems to be behaving a bit different than with the original chip in.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 11, 2020, 01:58:51 PM
What about pin 9?

Also measure on pin 3 of U41, since you have 2 channels measure with ch 1 on pin 3, with ch2 on pin 4. Since U41 is an inverter the signals should be exact the same but inverted.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 11, 2020, 04:55:12 PM
I'm sorry. I said pin 8. But meant pin 9.

I'll check those others now.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 11, 2020, 05:50:38 PM
Not much room to hook my probe on those pins, but here were my readings on pin 3 and 4 of u41. Bottom is pin 3, top is 4.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 12, 2020, 02:19:55 AM
Mmm very hard to see, does it still changes when you start up vs a second later?
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 12, 2020, 06:45:36 AM
That fade in and out was on pin 9 of u44

It does not do that anymore.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 12, 2020, 08:11:56 AM
But it still does the same thing, it starts up with the leds on the left then on the right and stops?

Long shot, but try to pull the RAM out (U31, either 5864 or 6264) and put it back in, this will clear the RAM. Do this with the unit off!!
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 12, 2020, 10:34:48 PM
Yes, the LED's behave the same. I notice the LED's only do that when the unit has been powered down for a while. If you start it up quickly after its been powered down, the led's don't really come on. Same with the screen.

I pulled out the ram. No change.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 13, 2020, 03:54:28 AM
Ok, check all the data and address lines on the eprom and RAM chip. Just look for activity on each pin.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 13, 2020, 07:42:43 PM
Seems to be activity on each pin of the data and address channels. Im not sure whether its proper readings but my scope reacted to each pin.

Id say if anything ,pin 2 (A12)of both chips seem to have a very faint /weak reading..
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 13, 2020, 07:48:11 PM
So interesting... in the middle of testing, the screen powered on for about a minute. It said no  and I pressed the edit button and it had a 9. I could see that it was trying to come on all the way. Then it faded out again. Thats the longest I've seen it come on. 

MarshallJMP. I was able to catch a video of this. I'll send it over.

Also. I notice the amount of time the screen stays on in the initial power up is longer than it was with the old u44.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 13, 2020, 08:35:12 PM
 I'm noticing pin 20 of the eprom seems to fluctuate between looking like this(see first attachment) and how it did earlier in this thread(see second attachment). So pin 20 of the eprom is not consistent.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 14, 2020, 06:59:08 AM
Pin 20 is also a chip select line (CS). Just like the RAM. Now these 2 have U41 in common. Just a suggestion, try to replace U41 and U40 if you can, see if that helps.

Edit;I just saw the video you send me, did this happen al of a sudden or when you were measuring? Maybe a bad contact somewhere? What happends if you push on the pcb near the ram/eprom or more to the right on one of those digital 74 IC's? Maybe a bad through hole somewhere?
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 14, 2020, 08:34:28 AM
It came on like in the video while I was testing, but I'm not sure if I was physically touching anything when it came on.

I tried pressing down on some of the IC's on the right... no luck

So I noticed just probing all the pins on U40 and U41 that only a handful of the pins actually showed a reading. So do you think I should go ahead and replace those?

Also, that reading on pin 20  of the eprom seems to really fluctuate a lot.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 14, 2020, 02:19:40 PM
Yes that's correct, U40 p 4,5,6, the rest is used in the reset circuit and stays at the same level after startup, same for U41, only p 1,2,3,4 will change. So you could try to replace them since they are cheap parts. On the other hand it could be something else. Could be a bad chip that is hooked to the address or data bus. If one of those inputs is pulling the bus down you can get some very weird behaviour. So it can be an adventure sometimes.  ;D
But I'll try my best to help you out the best I can, and I hope we can solve it.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on December 14, 2020, 04:32:58 PM
Would you like me to post pictures of all the data and address bus pin readings for the Eprom or the ram, or both?
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on December 16, 2020, 08:38:24 AM
No that would be too much work I guess.Just check to see if you have have signals.
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on January 08, 2021, 08:44:41 AM
So any updates?
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on January 10, 2021, 06:17:44 PM
So any updates?

I've been kinda busy.. had to put my mp1 in my storage shed for a bit.

I'll definitely be back at it soon!

Thanks MarshallJMP!
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on January 13, 2021, 12:38:05 PM
Ok just let us know.
Title: Re: MP-1 no display or LED's
Post by: andtimebegins on February 01, 2021, 03:35:25 PM
Well, sorry for the long delay in replies on this one... I ended up fixing the Mp-1!

Here is what happened:

A good deal on a working Mp-1 came up near me, so I bought it. I figured I'd try swapping out chips to see if that would make the broken one work... nothing. Then I figured I'd try swapping the transformers out just to be sure. I installed the working transformer into the broken Mp-1, and it started working!! :headbanger:

I figured I'd try the removed "broken" transformer into the other Mp-1 I had just gutted.. and now that one worked!! I noticed a bad crimp when removing the little wire connector on the white wire coming from the transformer. The wires weren't tightly connected to each other. I'm pretty sure that was the issue all along! So now I have two working MP-1's!!! YAY! :banana: :headbanger:

Title: Re: MP-1 no display or LED's
Post by: rnolan on February 01, 2021, 08:15:36 PM
 :whoohoo!:
Title: Re: MP-1 no display or LED's
Post by: MarshallJMP on February 02, 2021, 10:54:14 AM
Well that was strange, but hey it's fixed !!! Great job you did.
Title: Re: MP-1 no display or LED's
Post by: Iperfungus on February 09, 2021, 06:36:21 AM
We've a specific way, here in Italy, to indicate such blatant luck...  :lol: