Philips LDK4210 SPG

[ppppenguin]

Thanks. That dates the design to the early 1980s. I've got two different versions here on the bench. /01 and /02. The main differences seem to be in the PAL coder for the colour bar output. They use a couple of custom chips, OQ5501 (or 5506) and OQ5502. They are also used in the PM5519 portable test pattern generator for which the manual is readily available. They seem to do roughly the same jobs as the familiar SAA1043 and SAA1044 which are sync pulse generation and subcarrier coupling respectively.

After a bit of TLC, both SPGs seem to be working OK now. One had a very odd fault where the field drive pulse from the OQ5501 had a random mucky period at an an intermediate level that was neither logic 0 nor 1. This caused much havoc. By chance I put a 2nd scope probe on the signal and it settled down. A 33pF capacitor to 0V seems to do the job nicely.

I've also got a Courtyard CY420 SPG on the bench. I designed this c1989 and have managed to dig out all the schematics etc which have never been published. It's in a bad way. A National "Simple Switcher" was used to provide +5V for the logic. A 7805 has been bodged in, along with a couple of wirewound resistors to do most of the voltage drop. Makes the whole thing run rather hot. There's a lot that doesn't work. This seems to be mainly down to an 18CV8 programmable logic device. As far as I can tell, there's a blank, unprogrammed device in the socket. I think I have spares and I certainly have the ABEL and JEDEC files. I'm trying to borrow a programmer that can handle it.

I have a horrible feeling I'm dealing with a basket case but since I designed it I really ought to be able to get it working again.