Hey Tiido!

That’s a great spot! On mine, it looks like it has been simplified to R70 and R69, with the spot where R68 should be actually being a bridge to ground.

I lifted 70 and 69, and cut the bridge, but alas no change. Odd! I’ve put them back now anyhow.

It may remain an unsolved mystery… at least it does seem to otherwise work, and the SYSex above fixes some of those issues too!

I must thank you for your continued efforts on this, as well as your patience with myself- it’s very much appreciated 😀

I picked another one of these up, and it just so happened to be the earlier revision with the socketed CM-32L ROM. I did the mod again and observed the same results; no SFX on channel 10 unless you load in the SysEx file I made.

I did at least discover that the VPP doesn't need to be tied to VCC - I left it floating and it works absolutely fine.

Hi!
So, is a modded RA-50 totally equivalent to a CM-32L or not? I have found a couple of them at an interesting price and wondered if the modification is feasible and effective.
Thanks

Seems to be possible but whoever did it never posted a detailed guide, hopefully one day we will get one.

Mao wrote on 2024-11-04, 21:27:

Hi!
So, is a modded RA-50 totally equivalent to a CM-32L or not? I have found a couple of them at an interesting price and wondered if the modification is feasible and effective.
Thanks

It is, but to make it so you need to do the following:

• Add the missing SFX sample ROM that is missing (either via an additional 512K chip as I did, or by replacing the existing ROM with a larger 1MB 0ne as per Tiido's post.
• For some reason, the device doesn't initialise the SFX samples on channel 10 as a real CM-32L does. This doesn't affect games that are not expecting this mapping, but for those that do, you just need to send this SysEx file here to set the device up after powering it on.

I haven't posted any guide on how to do the mod as the posts here should cover what's required and some may want to do the neater modification of replacing the ROM entirely, but this does require de-soldering tools.

Cheers,
Rich

RichB93 wrote on 2024-11-08, 18:46:

It is, but to make it so you need to do the following: […]
Show full quote

Mao wrote on 2024-11-04, 21:27:

Hi!
So, is a modded RA-50 totally equivalent to a CM-32L or not? I have found a couple of them at an interesting price and wondered if the modification is feasible and effective.
Thanks

It is, but to make it so you need to do the following:

• Add the missing SFX sample ROM that is missing (either via an additional 512K chip as I did, or by replacing the existing ROM with a larger 1MB 0ne as per Tiido's post.
• For some reason, the device doesn't initialise the SFX samples on channel 10 as a real CM-32L does. This doesn't affect games that are not expecting this mapping, but for those that do, you just need to send this SysEx file here to set the device up after powering it on.

I haven't posted any guide on how to do the mod as the posts here should cover what's required and some may want to do the neater modification of replacing the ROM entirely, but this does require de-soldering tools.

Cheers,
Rich

Hi, hope this is not considered a necropost, i modded my RA-50to MT-32, it's a pretty straightforward work so no problem, now i'm interested in trying to do a complete CM-32L transformation but i didn't fully got what to do, also i never flashed a rom.

The easiest way for me to do that i think is to flash the whole CM-32L rom into one single 1Mb chip.

First problem is what programmer should i buy to flash a 27C801 ROM? I saw there are a lot of model, from cheap to very expensive, some may not provide the required writing voltage, some doesn't have update software to use on recent operating systems and some are claimed to not work at all (like the cheap Willem Eprom Programmer)... it's a mess for me and i need an advice to avoid buiyng something useless. I also would like use this programmer to save roms from old motherboards and isa cards, and reprogram them if corrupted.

Second problem, i didn't understood where to connect the A19 pin of the rom, Tiido's post says "a wire from A19 to the EPROM A19", but what is that A19 from to connect to the eprom A19?

Thanks for any help!

A19 is one of the pins (59) on the LA32 synthesizer chip, that is used as a !CE signal with 512KB sample ROM. For converting things to 1MB ROM you need to connect it to the actual A19 on the memory chip and then sever it from memory chip's !CE and then connect the !CE to ground so the memory is permanently enabled. That process should be matter of cutting a trace on the board and soldering two wires, but I don't know if there are any convenient locations to do so.

Tiido wrote on 2025-07-03, 15:23:

A19 is one of the pins (59) on the LA32 synthesizer chip, that is used as a !CE signal with 512KB sample ROM. For converting things to 1MB ROM you need to connect it to the actual A19 on the memory chip and then sever it from memory chip's !CE and then connect the !CE to ground so the memory is permanently enabled. That process should be matter of cutting a trace on the board and soldering two wires, but I don't know if there are any convenient locations to do so.

Thank you very much Tiido! If i understood correctly this could be achieved by bending the !CE leg of the rom and wiring to ground, and if the pin 59 of the LA32 is routed directly to the !CE pin i could just wire the A19 of the ROM to the !CE of the socket, also avoiding cutting the trace and having the mod easier to reverse, just in case.

Any suggestion on a programmer to buy, possibly that could also work (read and write) on older rom?

I am not a fan of bending pins but it is an option for sure, and you can run a wire from the !CE hole to A19 on the ROM, although that pin may also be connected to something and you may have to lift it also.

As far as programmer goes, I don't know, I use an expensive EE Tools Topmax II. I assume the cheap chinese things are all ok with 27C801, you can always check the supported chips lists on the documentations available.

The bigger problem is making sure the EPROM you get is actually properly erased. I.e if it is erased only for 15 minutes instead of 45, it may appear erased but the data storage cells are not actually fully recharged and the programmed content will be forgotten way before quoted data retention time (i.e under 5 years instead of 20+).

Tiido wrote on 2025-07-03, 17:03:

I am not a fan of bending pins but it is an option for sure, and you can run a wire from the !CE hole to A19 on the ROM, although that pin may also be connected to something and you may have to lift it also.

As far as programmer goes, I don't know, I use an expensive EE Tools Topmax II. I assume the cheap chinese things are all ok with 27C801, you can always check the supported chips lists on the documentations available.

The bigger problem is making sure the EPROM you get is actually properly erased. I.e if it is erased only for 15 minutes instead of 45, it may appear erased but the data storage cells are not actually fully recharged and the programmed content will be forgotten way before quoted data retention time (i.e under 5 years instead of 20+).

Thanks for the suggestions, time to buy some stuff!

I need some clarification, the M27C801 rom has 4 more pins than the AM27C512 in the RA50, the board has the spots for the pins are connected as follow:

- A19 (1), A18 (31), VCC (32), are VCC
- A16 (2) is ground

Also if i put the M27C801 in the socket (with the four extra ping hanging out of the socket) it ends up having the pin A17 (30) connected to VCC. All the other pin looks like being equivalent between the two roms.

So, is the mod thought as the M27C801 as a drop in replacement? In that case it will have the address lines as follows:

A1 to A15 same as the old rom
A16 = ground
A17 = VCC
A18 = VCC
A19 = jumpered to !CE

Is that correct? I was expecting A16 to A18 ground and only the address line that "switches" between the to halves (which i suppose is A19) to change based on the chip enable signal

I attached the two pinouts and a photo of the board.

IC20 is the sound ROM that needs replacing, not the CM-32L UVPROM.

Thank god i asked, i was going to make a mess! I got confused while reading other discussions, one of them was talking about that CM32 rom and it got stuck in mi mind. Thanks!
Stuff on it's way, soon i will try the mod! (finger crossed!)

I made a mess desoldering the rom, i didn't noticed that there was A LOT of solder also on the upper side and i'm not able to use the copper wick properly, soi got quite mad 🤣 The end results are the vias really beaten up, a lot of material scraped from the upper side and two broken traces... looks like a managed to repair the traces but with nothing in place, hope the thin wires won't detach when i will solder the socket, don't know if i can make the repair again with it.

Anyway, while i'm waiting the replacement rom and the socket i dumped the the desoldered rom (looks like it survived) and the two socketed roms labelled "CM-32 L" (the control rom of the CM-32L part) and "RA-50" (the control rom of the sequencer, i guess). I made i visual comparison (without having any clue) with the control rom of a real CM-32L downloaded from internet archive and there are some differences but i don't know what actually is different except for obvious strings. As an example some string are (RA-50 vs real CM-32L):

- "** Roland MT-32 **" vs "**** Roland ****"
- "PCM REV. OFF CENTER" vs PCMA REV. OFF CENTER"
- "PCM REV.1 ON L CH" vs "PCMB REV.1 ON L CH"
- "PCM REV.2 ON R CH" vs "PCMA REV.2 ON R CH"

What i would like to understand is what causes the problem that the modded RA-50 doesn't map the sounds effects on channel 10 (as discussed in another thread where a software fix was posted, didn't tried myself yet). Maybe it's a fixable thing and an hardware only mod would be possible.

One thing i thought was to use the CM32-L control rom from the RA-50 in munt or scummvm or some other emulator to see if the problem with the sound effects not on channel 10 is present, but i don't know the level of emulation and if the control rom is actually executed as it is or it is totally or in part replaced by a piece of software.

Another thing i could do is to flash a real CM-32L rom and put into the RA-50 and see what happen, but i don't know it it would be safe to do.

Finally, but it goes way beyond my skills, try to understand if the the mapping of the sounds effect in missing in the "CM-32 L" control rom and possibly patch it to add the mapping, or if the "RA-50" rom is messing with it and patching it to avoid the interference. Maybe i could try to power the RA-50 without the RA-50 rom and see what happens after installing the full pcm rom.

Hope somebody is interested, any suggestion or help is appreciated, thanks!

L-C wrote on Yesterday, 16:27:

I made a mess desoldering the rom, i didn't noticed that there was A LOT of solder also on the upper side and i'm not able to us […]
Show full quote

I made a mess desoldering the rom, i didn't noticed that there was A LOT of solder also on the upper side and i'm not able to use the copper wick properly, soi got quite mad 🤣 The end results are the vias really beaten up, a lot of material scraped from the upper side and two broken traces... looks like a managed to repair the traces but with nothing in place, hope the thin wires won't detach when i will solder the socket, don't know if i can make the repair again with it.

Anyway, while i'm waiting the replacement rom and the socket i dumped the the desoldered rom (looks like it survived) and the two socketed roms labelled "CM-32 L" (the control rom of the CM-32L part) and "RA-50" (the control rom of the sequencer, i guess). I made i visual comparison (without having any clue) with the control rom of a real CM-32L downloaded from internet archive and there are some differences but i don't know what actually is different except for obvious strings. As an example some string are (RA-50 vs real CM-32L):

- "** Roland MT-32 **" vs "**** Roland ****"
- "PCM REV. OFF CENTER" vs PCMA REV. OFF CENTER"
- "PCM REV.1 ON L CH" vs "PCMB REV.1 ON L CH"
- "PCM REV.2 ON R CH" vs "PCMA REV.2 ON R CH"

What i would like to understand is what causes the problem that the modded RA-50 doesn't map the sounds effects on channel 10 (as discussed in another thread where a software fix was posted, didn't tried myself yet). Maybe it's a fixable thing and an hardware only mod would be possible.

One thing i thought was to use the CM32-L control rom from the RA-50 in munt or scummvm or some other emulator to see if the problem with the sound effects not on channel 10 is present, but i don't know the level of emulation and if the control rom is actually executed as it is or it is totally or in part replaced by a piece of software.

Another thing i could do is to flash a real CM-32L rom and put into the RA-50 and see what happen, but i don't know it it would be safe to do.

Finally, but it goes way beyond my skills, try to understand if the the mapping of the sounds effect in missing in the "CM-32 L" control rom and possibly patch it to add the mapping, or if the "RA-50" rom is messing with it and patching it to avoid the interference. Maybe i could try to power the RA-50 without the RA-50 rom and see what happens after installing the full pcm rom.

Hope somebody is interested, any suggestion or help is appreciated, thanks!

I'd love to figure this out too to be honest - I'm glad that I was able to at least map the missing sounds with SysEx, but it would be nice to have it ready to work from power on without having to do that. I must admit, I've not tried flashing another CM-32L ROM and trying it in mine; I assumed that as it was labelled CM-32L that is is exactly the same as a ROM from an actual CM-32L.

As for the PCM ROM that you desoldered, that is definitely identical to what is used in an actual CM-32L - the part number matches what is in a CM-32L, and I was able to overlay the top half of the ROM on top as you probably read earlier in this thread.

I'm going to dump the CM-32L ROM in my RA-50 and compare it against CM-32L ROM dumps online just to be sure.

So I had a look at my unit, and it appears to have a v1.00 ROM which, apart from a minor 'clicking' audio bug, is otherwise just a normal CM-32L ROM.

Nevertheless, I replaced it with a v1.02 ROM found online, but alas, still no change regarding the extra missing instruments.

I'm sure the resistor section that was previously mentioned has something to do with it, but I've not played with it enough to figure out just what needs to be done. If anyone else wants to take a crack at it - there are service notes for the RA-50 and the CM-64 available online - I've spent a few hours staring at them side by side but I can't figure out where the difference is - they look pretty much the same to me. Also, if you really want to pimp your RA-50, it's technically possible to add the LCD of the MT-32 back, as well as the buttons! They're used for test mode on the CM-64, and as the ROM is the same in the RA-50, it's absolutely doable. Would take some impressive modification though I'm sure.

I've attached the v1.00 ROM to this post as a curiosity for anyone looking for it (not sure why you'd want it!) purely as I can't see it available anywhere else online.