Hi,
I'm new here, but I've been reading this forum for years.
Now it's time to say good morning to everyone!
Currently, I am hoping that one of you will help me. I have a VP-7722A with a dead DSP card, it does all the measurements fine but THD1 and THD2 are missing. I measured everything on this card pulled from unit on the extension and it looks like either the CPU or the PROMs are dead, in some cases the CPU does not respond to the RST signal with no traffic on the RD or WR lines and sometimes reads data from AD and main controller at strange intervals.
The question is - does anyone have a copy of the data stored in the AM27S191DC PROM? Mine were numbered 06490 and 06501. So i can compare.
Thank you in advance, it would be nice to have it back to full life, working properly, it is such a nice unit.
Cheers
- Lukasz
I'm new here, but I've been reading this forum for years.
Now it's time to say good morning to everyone!
Currently, I am hoping that one of you will help me. I have a VP-7722A with a dead DSP card, it does all the measurements fine but THD1 and THD2 are missing. I measured everything on this card pulled from unit on the extension and it looks like either the CPU or the PROMs are dead, in some cases the CPU does not respond to the RST signal with no traffic on the RD or WR lines and sometimes reads data from AD and main controller at strange intervals.
The question is - does anyone have a copy of the data stored in the AM27S191DC PROM? Mine were numbered 06490 and 06501. So i can compare.
Thank you in advance, it would be nice to have it back to full life, working properly, it is such a nice unit.
Cheers
- Lukasz
Have you checked the more likely failures that would cause those symptioms? Power at the chips Local bypass caps Master clock etc. Those and similar things are more common failures. And much easier to fix. There is somewhere on EEVblog forum I think a place where people are storing prom images. A google search may help.While they do fail its not common.
It takes me almost a week to dig into the circuit, thinking there must be some obvious reason. The first visible defect was a leaky battery and corroded traces on the AD board. I thought this would solve the problem because its close sampling signal generator - which is active during DSP operation, but it doesn't. I measured each signal, checking TTL levels, looked for abnormal operation with the logic analyzer - there is no sign of bad behavior. Everything leads me to believe that the problem is in the CPU, PROM, RAM and area. Especially since at some point the CPU stopped working without any reaction to reset and without generating WE and DEN signals. This chip gets quite hot at 20MHz, just like the PROM. So maybe the problem is the processor. I check it when a new one arrives, luckily there are some nos ones on ebay . PROMs are more problematic - I cannot program them, and converting them to eprom is not simple/possibly easy. I found eprom data for the rest of the device on the Internet, but not for the DSP. If anyone has seen it, please let me know.
I hope replacing the processor will help. Or maybe there is another, really stupid simple reason
I hope replacing the processor will help. Or maybe there is another, really stupid simple reason
I finally managed to get the DSP working . The problem was, as I suspected, a fried signal processor . The replacement finally arrived and after connecting it without any excuses, the measurements in THD1 mode begin to appear. I replaced the blower and added an extension made from the old one, because it had some strange dimensions of 33mm wide.
I also added some heatsink to cover the PROM and CPU as it gets quite hot at 20MHz.
. The problem was, as I suspected, a fried signal processor . The replacement finally arrived and after connecting it without any excuses, the measurements in THD1 mode begin to appear. I replaced the blower and added an extension made from the old one, because it had some strange dimensions of 33mm wide.
I also added some heatsink to cover the PROM and CPU as it gets quite hot at 20MHz.