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Remove caps from board and use a cap meter on them (and also look for shorts). You can't easily measure them in-circuit. Also, be very careful about repeated DAC rework and mechanical pad strain. The device pads are generally subject to heat fatigue after multiple cycles and are at increased...

@jamcz The -ES2 may work OK. There may be a datasheet or databook somewhere that documents the changes. But, with any luck, the board may soon be working!

Try octopart.com or findchips.com. Octopart is better, in general. There should be a direct ADV drop-in and maybe more options than a Bt473. https://octopart.com/search?q=adv473kp110es&currency=USD&specs=0 The K is temp range/grade - 0-70C The P is package - Plastic/maybe PLCC, etc. The J is...

You have to identify the problem first...but it does feel like a timing issue. ;-) @jmacz: yes - The retro stuff is fun. I wish I had more time or awesome cloning technology. One of my clones would definitely just want to mess around on retro Macs and program in pre-CFM, flat memory 68K...

Hmm...since you have a scope, compare the sync width and shape between the PC-8 and Spectrum/24 III. The rework cap on the Bt output that is bent over the top of the part on Spec/24 III (which I think is on green - but check the pins) is there to minimize vertical line shadowing (voltage...

Great! v1.1 will definitely work better for you. It still has some bugs, but you would probably have to work to find them. :-D

Good luck! Via/soldering failures are always a possibility on old PCBs. So, maybe that was it. If there is screen garbage in 24-bit mode, it most likely has to do with timing/translation failures relating to the PALs/GALs on the daughtercard.

Good job. I think the Bt473 and ADV473 were interchangeable, but if you can find a matching ADV473 as NOS (New Old Stock), etc., then that is the probably the fastest solution. Or, look at both spec sheets -- it should be apparent if you can use either part - pinouts, voltages, packages, etc...

Also, for those of you who have PDQ+ boards, just put a Thunder ROM on them (as noted in my post above). It should work and will have faster acceleration performance. They are the same board. The only difference is that the PDQ+ doesn't have the GWorld RAM slots that the original Thunder...

You should update to v1.1 if you can manage it. The 1.1 ROM was much better, more stable and had additional video configs. The only major functional loss was lock menubar, traded for quick panning that allowed you to pan the screen from anywhere. Lock menubar had many bugs and compatability...

There are definitely reasons why SuperMac 2nd sourced them in 1988-89. Not being able to ship boards because of CLUT failures was a slight financial impediment. ;)

It's the same -- it just sets/replaces the active config/sRsrcs for the board. If you only have 1 monitor, then you probably need Round Robin, since cable sense was limited on that board -- I forget -- maybe Apple 13" and 19" 1024x768 75Hz used it...maybe also Apple 16" , but not 19" 1024x768...

Initially, SuperMac (pre-Radius merger) originally used Bt/Brooktree parts exclusively, but eventually had to develop Analog Devices as an alternate, lower cost source. I think the use of ADV parts came about because of a bad run of Bt478 parts and/or related supply chain issues in 1989(?). The...

On the Thunder IV, the final output is coming from the ADV473, which I think was a cheaper, drop-in replacement for the Bt473 -- 24-bit CLUT/DAC. The video signal should be sync on green (for the old trinitrons and hitachi clones), so if there is no green output, then there won't be any image...

Edit -- oh -- I didn't see the replies above...I see that you reflowed...but -- also make sure you didn't change systems or reset the slot, as below. I recall it being a software issue. But...in reading about your debugging, it sounds like you already tried software/slot stuff. So, I guess...

With the Spectrum/24 Series III, the problem may be that you are using the board in a non-cleared slot. Make sure you clear the slot PRAM before trying the board so that it will go into Round Robin by default (cycling configuration choice where you hit the space bar to set the config) at...

@EIMS -- The board you have is basically a Thunder/24 card. It was originally designed/released in late 1991 with spins in 1992 as the next generation after the original Spectrum/24 PDQ as the board that switched to a newer graphics controller (SMT02), bit-shift registers (BSR03) and a custom...

Good work on everything. The latest Spectrum/8 Series III ROM is v1.3 -- it added a number of new video configs, etc. Commented elsewhere. The latest Spectrum/24 Series III ROM is v1.1 (no 3.x update). It fixed many problems that were present in the v1.0 ROM. Commented elsewhere. The latest...

The Spectrum/24 PDQ is a good card and was the fastest board upon its release. Initially, I think it was the only board with 24-bit graphics acceleration on 21" at 1152x870. So, it had an initial stand-alone advantage for Mac desktop graphics/design/publishing which drove sales of the boards and...

I played around briefly with my original PDQ board and remembered a few more things. You should be fine with SuperVideo 2.49 (from 1992) or maybe 2.7. The version that originally shipped with it was 2.06ish (I think), but I remember a problem with Apple 12" and 13" monitors not displaying the...