What PSU are you using? Can't recall now whether the SC-88VL's PSU is also integrated like the SC-88 Pro.
Regardless, could be a PSU issue (it's not outputting enough amps).

On the VL it's an external PSU. My SC-55 MkII is working fine on the same PSU.

diskers wrote:

On the VL it's an external PSU. My SC-55 MkII is working fine on the same PSU.

How many amps does the SC-55 draw compared to the SC-88VL? Could be that the PSU is just outputting not enough amps for the SC-88VL.

Anyone have any idea what can be the culprit?

EPROM failure, most likely.

How many amps does the SC-55 draw compared to the SC-88VL?

Both are rated 500 mA afaik.

OK as I have a programmer I can try to read the prom. What can be a replacement for the HN62448P, the 27C4096?

PS. However on the hitachi datasheet the HN62448P is a 42 pin device but here on the the Roland PROM marked HN62444BP there's 40 pins though...

PS. OK I made a mistack it's HN62444BP 40 pin mask eprom.

It could also be a bad connection between the display circuit board and the other circuit board(s), or between the display and the circuit board it's on (gets power, no data). If the cables use connectors, you can try pulling them out and reinserting them.

You should be able to check whether it's the display only, or something more serious by attempting to play a MIDI file. Sound comes out => display (connections), no sound => something else.

Hi,
I already tested if there is any output from the module. No output, so it's probably something different than the LCD circuitry.

Also I checked the DIP socket pinout. A 5.02V current on pin 40 is delivered.

Ok guys it's most probably the prom. When probing the DIP socket on VCC and VSS it's steady 5.02Volts. When PROM is inserted only 1.92V . So the question is how to get a replacement I don't think that even Roland still have those on stock.

Anyone have a binary dump of this prom?

I have a SC88VL but I have never opened it; I have a TL866 also. If I have time in the next day or two I'll try to dump the eprom.

(edit) The chip is socketed, right? I wouldn't want to have to desolder/solder a 40pin DIP. 😀
Also the HN62444B is not in the list of supported chips for the TL866, but the HN27C4096G is - and it seems pin compatible (probably the erasable version of the OTP 62444). I will try to see if my programmer accepts to dump it as that chip. It may, or it may not we shall see.

Okay it worked. I've dumped it as HN27C4096. See attached. You should have no trouble to burn that into an 4096 chip.

Hi,
Thanks a lot. The strangest thing is that yesterday I dumped my PROM on my programmer. So I don't really know what's the problem. Maybe the PROM is defective, in the way that to get functional it strains an amperage that the Roland can't provide and my programmer with an external PSU can. Anyway your dump will be very useful to compare the PROM even if they are not the same version. However it also can be some capacitors, power regulators or even a dead CPU.

Cool. Keep us posted, just in case some day I get to deal with the same problem I'll have a reference. 😀

could just be ribbon cable shifted that goes to the lcd.

diskers wrote:

Ok guys it's most probably the prom. When probing the DIP socket on VCC and VSS it's steady 5.02Volts. When PROM is inserted only 1.92V . So the question is how to get a replacement I don't think that even Roland still have those on stock.

This might be the key to your problem. And I think the trouble is with the board rather than the PROM, especially since it reads OK. Surely there are more 'scientific' ways to find out if it draws an abnormally high current, but for a quick&dirty test you can try and read it a few times in a row, it should get fairly hot if defective.

Isn't the +5v common to all the chips on the board? If it drops to 1.92V with the PROM installed, are the rest of the chips undervolted the same?

quicknick wrote:

And I think the trouble is with the board rather than the PROM, especially since it reads OK.

A bad ROM will read fine as well, it will just have flipped bits. You need to compare the dump to a known-good one before you can say whether the ROM is ok or not.

BloodyCactus wrote:

could just be ribbon cable shifted that goes to the lcd.

The unit does not work at all, so it's not just the display. Also, the cables Roland uses are more or less connected for eternity, they can't shift.

A PROM so defective/shorted that will draw enough current to sag the supply voltage by 3 volts will not output anything on any programmer...

I guess 2 things can be tested:
1. compare his dump to the one I posted above which is from a known good unit
2. if the same or very close, burn either of them in a 27C4096 and install that in the PROM socket, see if that fixes the problem.

But it's possible that there is a problem somewhere else on the board as well. From the datasheet, the HN62444 should be drawing a maximum of 100mA from 5V. That should not drop the Vcc to below 2V. And yes, the other chips won't function at 2V either.