here is the MCB-1 schematic from my service manual, are you sure you did not make a mistake?

keropi wrote on 2020-05-02, 22:13:

here is the MCB-1 schematic from my service manual, are you sure you did not make a mistake? […]
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here is the MCB-1 schematic from my service manual, are you sure you did not make a mistake?

No mistakes from that schematic, but I accidentally reversed the pinout on the inverter chip. I'll fix it soon and report back the results with some pictures.

After I have confirmed that it works as intended I will design a nice case for it.

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The small "-" sign in one corner of the chip indeed means pin 1 and not VCC-.

I follow this schematic of the 74LS05 chip: https://www.circuitspecialists.com/74ls05.html

I soldered the live wire to pin 14, ground to pin 7 and used gates 11-10 and 9-8 for the TXD-in/out. There are no shorts or mistakes anywhere.

Here are some pictures of my creation:
https://i.imgur.com/vJW1oW5.jpg
https://i.imgur.com/Iqo3E7E.jpg
https://i.imgur.com/u4krTP1.jpg

Is there any way I can check if the chip or the MIDI-port of my LAPC are faulty?

EDIT: Turns out I actually mada a mistake and reversed the pins on the DB15 connector. Illogical that the DIN connector pins are counted from the back and the DB15 port pins from the front. I have now soldered them in the proper order. Too bad it didn't change anything and the unit still doesn't transmit any signal to the MT-32. Did I fry the chip with the incorrect pin order? Basically I had connected one live wire to ground and another to TXD, while ground was connected to VCC.

The 15 pin D connectors will have the pin numbers embossed in the insulator body on the wire side. Yup, they're tiny and hard to see too. Also keep in mind that "male" and "female" connectors will have pin numbers that are a mirror of each other so that pin one goes to pin one. Yeah, yeah, I know that's pretty obvious, but, well, you do it enough times and, yup, I've mixed that up at least once, so figure I'll mention it. In "official" vernacular the part of the connector with the pins (male) is usually designated with a "P" for pins and an "S" for the "female" part as the contacts are "sockets".

On the 74LS05, the notch is what indicates the direction of the chip. Sometimes, instead, there is a noticeable dimple just inside of pin 1. Either one will indicate what I'll call the "top" of the chip and the assumption is looking at the side with the printing/number on it (away from where the pins point, which I guess could also be considered the "top" too). With that notch (or the dimple) pointing away from you, pin 1 is on the left side and pin 14 is on the right. It seems that you have some technical ability, and I will apologize if I seem like I'm being condescending, but since I don't know the depth of your knowledge, and for others that might read this, I'll just point out, that on a plastic DIP IC like that, the pins are 1-7 on the left side from top to bottom, and from 8-14 on the right side with 8 being at the "bottom" and pin 14 being across from pin 1.

I'm curious if your adapter works. Been looking for an MCB-1 to mate to my LAPC-I as a set. Just missed a really clean one on e-bay because I wasn't paying attention.

I might have some time in the next few weeks to mess with this. However, I know nothing about music, other than listening. So a complete neophyte when it comes to MIDI stuff and how the MPU-401 actually works. I got the card years ago for audio for a couple of games I used to play that needed an MPU-401 for best sound. Actually sill have the card plugged in the computer I used then. (Uh, well, maybe I do kinda hoard tech type stuff.)

Ok, IF I were to attempt to recreate the MCB-1, let's start with what software do I need to test it to make the LAPC-I output something on the MIDI port? I have a number of systems with ISA slots so have a number of processors that I can try with different operating systems. I KNOW the card works with the system it's in with, uh, dang, don't even remember the game. But I powered it up a few years ago on my bench and tested the RCA outputs, which worked fine. I have a pretty complete bench here, with a good scope, and a variety of ways to play audio. But I don't have any music equipment. Cross that bridge later.

And just a note, I'm in Tucson AZ.

Karl

Paddan1000 wrote on 2020-05-03, 09:58:

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The sma […]
Show full quote

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The small "-" sign in one corner of the chip indeed means pin 1 and not VCC-.

I follow this schematic of the 74LS05 chip: https://www.circuitspecialists.com/74ls05.html

I soldered the live wire to pin 14, ground to pin 7 and used gates 11-10 and 9-8 for the TXD-in/out. There are no shorts or mistakes anywhere.

Here are some pictures of my creation:
https://i.imgur.com/vJW1oW5.jpg
https://i.imgur.com/Iqo3E7E.jpg
https://i.imgur.com/u4krTP1.jpg

Is there any way I can check if the chip or the MIDI-port of my LAPC are faulty?

EDIT: Turns out I actually mada a mistake and reversed the pins on the DB15 connector. Illogical that the DIN connector pins are counted from the back and the DB15 port pins from the front. I have now soldered them in the proper order. Too bad it didn't change anything and the unit still doesn't transmit any signal to the MT-32. Did I fry the chip with the incorrect pin order? Basically I had connected one live wire to ground and another to TXD, while ground was connected to VCC.

After looking at your pictures and looking at the schematic of the MCB-1, maybe I'm just not looking at it properly, but, are the pictures of how your circuit is now connected? Because it looks like you have pins 8 and 15 of the D connector tied together. And I as of yet (still looking it over) don't see a direct connection from pin 7 of the chip to pin 11 or 12 of the D connector.

And as of yet, (still looking it over) I don't see a direct connection from pin 7 of the chip to pin 11 or 12 of the D connector.

On that chip, while yes, the small "-" is next to pin 1, typically you would use the notch at the end as the indicator of which end pin 1 is on. If there is a notch on one end of the chip, always use that as as your indicator for pin 1. Although I don't remember ever seeing positive or negative indicated like that on a chip of that type before, I wouldn't say that it "never" happens, but if there is a notch on the end of a chip, use that and the manufacturers pinout diagram to determine which connections go to which pins.

Karl

Paddan1000 wrote on 2020-05-03, 09:58:

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The sma […]
Show full quote

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The small "-" sign in one corner of the chip indeed means pin 1 and not VCC-.

I follow this schematic of the 74LS05 chip: https://www.circuitspecialists.com/74ls05.html

I soldered the live wire to pin 14, ground to pin 7 and used gates 11-10 and 9-8 for the TXD-in/out. There are no shorts or mistakes anywhere.

Here are some pictures of my creation:
https://i.imgur.com/vJW1oW5.jpg
https://i.imgur.com/Iqo3E7E.jpg
https://i.imgur.com/u4krTP1.jpg

Is there any way I can check if the chip or the MIDI-port of my LAPC are faulty?

EDIT: Turns out I actually mada a mistake and reversed the pins on the DB15 connector. Illogical that the DIN connector pins are counted from the back and the DB15 port pins from the front. I have now soldered them in the proper order. Too bad it didn't change anything and the unit still doesn't transmit any signal to the MT-32. Did I fry the chip with the incorrect pin order? Basically I had connected one live wire to ground and another to TXD, while ground was connected to VCC.

commtech wrote on 2020-06-15, 00:52:

After looking at your pictures and looking at the schematic of the MCB-1, maybe I'm just not looking at it properly, but, are th […]
Show full quote

After looking at your pictures and looking at the schematic of the MCB-1, maybe I'm just not looking at it properly, but, are the pictures of how your circuit is now connected? Because it looks like you have pins 8 and 15 of the D connector tied together. And I as of yet (still looking it over) don't see a direct connection from pin 7 of the chip to pin 11 or 12 of the D connector.

And as of yet, (still looking it over) I don't see a direct connection from pin 7 of the chip to pin 11 or 12 of the D connector.

On that chip, while yes, the small "-" is next to pin 1, typically you would use the notch at the end as the indicator of which end pin 1 is on. If there is a notch on one end of the chip, always use that as as your indicator for pin 1. Although I don't remember ever seeing positive or negative indicated like that on a chip of that type before, I wouldn't say that it "never" happens, but if there is a notch on the end of a chip, use that and the manufacturers pinout diagram to determine which connections go to which pins.

Karl

Paddan1000 wrote on 2020-05-03, 09:58:

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The sma […]
Show full quote

Apparently the chip pinout should be interpreted from above after all and not the bottom, which means I made no mistake. The small "-" sign in one corner of the chip indeed means pin 1 and not VCC-.

I follow this schematic of the 74LS05 chip: https://www.circuitspecialists.com/74ls05.html

I soldered the live wire to pin 14, ground to pin 7 and used gates 11-10 and 9-8 for the TXD-in/out. There are no shorts or mistakes anywhere.

Here are some pictures of my creation:
https://i.imgur.com/vJW1oW5.jpg
https://i.imgur.com/Iqo3E7E.jpg
https://i.imgur.com/u4krTP1.jpg

Is there any way I can check if the chip or the MIDI-port of my LAPC are faulty?

EDIT: Turns out I actually mada a mistake and reversed the pins on the DB15 connector. Illogical that the DIN connector pins are counted from the back and the DB15 port pins from the front. I have now soldered them in the proper order. Too bad it didn't change anything and the unit still doesn't transmit any signal to the MT-32. Did I fry the chip with the incorrect pin order? Basically I had connected one live wire to ground and another to TXD, while ground was connected to VCC.

Thank you for your responses. I resoldered the DB15 port correctly according to the small numbers embossed next to the pins. I've double checked that the pins of the chip and the pins of the DIN connectors also are soldered correctly and that there are no breaks in the circuits. It still doesn't work and I don't really have any technical background or access to anyone else who has who can help me diagnose if the problem lies with the chip. I've tried two different chips and it didn't work with either. I've given up for now, but I suppose that when I try next time I will get a socket for the chip so I don't have to solder in on directly and risk damaging it.