Hi Members,
Few years back, I had developed an MCS51 based product for one of my clients. Since then, he is manufacturing about 50 Nos. per month, and is quite satisfied with it. This product is using AT89C52 (even today we get fresh ones here, believe it or not!!!). Many years ago, I had told my client to use P89C52X2BN. But he faced lots of Noise problems with it. He never wanted to investigate it why, but in the very same product AT89C52 worked very well without any problem. So, he always insisted on using AT89C52. He is not satisfied with even the AT89S52. My problem is not in this area, the problem is as explained below:

About 2 months back, he had lots of problems with the CPU AT89C52. The problem he traced out was that the crystal was not working properly; It turned out that most of the suppliers in Mumbai were selling the new lot of crystals. So he had to run to every supplier in Mumbai to get the crystal of old lot. Somehow he managed to get it, and he has stocked it for next 4 months of supply. I had asked for that crystal for analysis, and found that the crystal does not work with AT89C52 at all. But it works perfectly fine with Philips MCU. I tested it with P89C52X2BN, P89C61X2BN, P89V51RD2BN and P89C51RD2HBP(I happen to stock the old one as souvenier, just in case I might need to test it in situations like these).
I refered to datasheet of Atmel and it says 30pf for +10pF for crystals. I tried the AT89C52 even with 33pF, but did not work.
So now my questions:
1. How do we know what should be the value of the capacitor for using with MCS51? with Atmel, Philips, Dallas, etc....
2. How can we test whether the crystal is working or not working even before we solder the crystal ? Any links to Testing circuit schematic will be a lot of help.

Thanks.