CSQ-600.

 A few years ago, I acquired a Roland CSQ-600 sequencer in very poor condition and downright out of order.

I have been troubleshooting this machine for some time. After some investigation I have only found one broken LED so far. 

However, I still find it completely impossible to start the CSQ-600. On the oscilloscope, the processor seems totally frozen. No scanning is performed on the buttons for example. So I suspected a problem with the processor.

I therefore bought on eBay a new processor equipped with the correct firmware. After replacing the old processor with the new one, the result is the same. The CSQ does not start.

So I wondered if the processor bought on eBay was indeed well programmed. But how do you know?

After some research, I discovered that someone had developed a small board capable of programming and reading this type of CPU.

All the information for the realization of this board is available here. So I made a copy of this programmer. The author has slightly modified the layout of the components but the operation remains the same. 

This material is used with a small software allowing to read and program a certain number of old circuits of which the 8048.

So I performed a memory dump of the two processors, the original one, and the one bought on eBay. What was the result?

Well the dump of these two circuits is strictly identical.

However, I noticed a rather strange phenomenon. After a few tens of seconds, the original 8048 of the CSQ-600 gave absolutely anything during new dumps.

While researching CSQ-600 troubleshooting info, I had occasion to read comments that the processor seemed to have this kind of problem. That is to say that when it was powered, a few tens of seconds later, the dump began to 'spin'.

I performed the test myself by cooling down the CPU and then testing it again. Indeed, after a few tens of seconds, the dump is no longer valid.

Ok, I've made some progress on the subject but... that still doesn't tell me why the CSQ-600 won't start!!! I got a disassembler, so I'm going to study the ASM source to see if the CPU does any test before starting the application. I will also try to test its start cycle with the logic analyzer.

What seems obvious now is that it is useless to perform these tests with the original processor. It definitely looks faulty!

And in fact, I also now own the binary code of the processor....