Supermac Spectrum/24 Series III and Series IV Issues

[jmacz]

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. Check the output on the ADV473...and that is something you may be able to replace. The DAC may be blown/ESD'd from the connector side.

Thanks for the pointer on ADV473, I'll take a more detailed look around that chip.

I think the sync is fine as I'm seeing an image and it's not distorted. The only issue is that the color is bluish. I have a picture of it higher up in this thread (the picture of a very blue Share window). I do see output from the green pin but the voltage seems very low. And nothing on red (which explains the blue).

 

[jmacz]

Radius used them on their PrecisionColors. Got one in the post over the weekend for a project to upgrade a PrecisionColor 24xk into a PrecisionColor 24x (80MHz RAMDAC to 110MHz).

Radius used a mix of Analog Devices and Bt parts.

View attachment 58199

Oh nice! Glad to see you can still procure this. Thanks for the tips guys!

 

[MacOSMonkey]

Radius used them on their PrecisionColors. Got one in the post over the weekend for a project to upgrade a PrecisionColor 24xk into a PrecisionColor 24x (80MHz RAMDAC to 110MHz).

Radius used a mix of Analog Devices and Bt parts.

View attachment 58199

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 problem affected main production of Spectrum/8 Series III when SuperMac had no alternate, approved source and also resulted in RMAs. Some of the boards displayed pixel garbage in the output video - maybe temperature or timing sensitive. So, they built a test run of boards with comparable ADV parts and eventually shipped ADV as a primary source. Thereafter, Brooktree and ADV competed for use on SuperMac products...and that was probably a good thing in terms of COGS (Cost of Goods Sold).

 

[Phipli]

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 problem affected main production of Spectrum/8 Series III when SuperMac had no alternate, approved source and also resulted in RMAs. Some of the boards displayed pixel garbage in the output video - maybe temperature or timing sensitive. So, they built a test run of boards with comparable ADV parts and eventually shipped ADV as a primary source. Thereafter, Brooktree and ADV competed for use on SuperMac products...and that was probably a good thing in terms of COGS (Cost of Goods Sold).

I know it is kind of a silly thing, but Analog Devices were always friendly and generous when I ordered samples as a student. That and I like their laser trimmed thermocouple amplifiers...

Never had any dealings with Brooktree... because I've never built a video card

 

[MacOSMonkey]

I know it is kind of a silly thing, but Analog Devices were always friendly and generous when I ordered samples as a student. That and I like their laser trimmed thermocouple amplifiers...

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.

 

[jmacz]

Was working great for the last week until yesterday it started happening again (albeit now nearly as bad as before). Previously, I couldn't get any part of the screen to refresh/erase/redraw properly after switching to 24bit. Now, most of the screen is fine but I get random artifacts after a cold boot, and eventually it goes away. Happens in both 8 bit and 24 bit modes now (whereas it was 24bit only before). Again, only when acceleration is enabled. Going to try reflowing the entire mainboard as well.

Reflowed the entire 24/III main board (and the daughter card again). So far it's holding up after a cold boot. Hope it sticks this time..

 

[jmacz]

Received my second IIci and got tied up recapping it and converting yet another ATX power supply for it. Finally finished with that so going back to debugging this 24/IV now. Will check out that ADV chip.

 

[jmacz]

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. Check the output on the ADV473...and that is something you may be able to replace. The DAC may be blown/ESD'd from the connector side.

It looks possible that you might be right.

I found the data sheet for the ADV473 and checked the pins while the IIci was running.

• IOR (37) - Red Output - 0.00V (matches pin 2 on the DB15)
• IOG (38) - Green Output - 0.19V (matches pin 5 on the DB15)
• IOB (39) - Blue Output - 0.89V (matches pin 9 on the DB15)
• Vrefin (43) - Voltage Reference Input - 1.2V
• Vrefout (44) - Voltage Reference Output - 2.4V (I think this is supposed to match the reference input at 1.2V?)
• R0 - R7 (45-52) - Red Inputs - Between 0.5V and 2V (white screen had mostly 2Vs and black screen had mostly 0.5Vs)
• G0 - G7 (53-60) - Green Inputs - Between 0.5V and 2V (white screen had mostly 2Vs and black screen had mostly 0.5Vs)
• B0 - B7 (61-68) - Blue Inputs - Between 0.5V and 2V (white screen had mostly 2Vs and black screen had mostly 0.5Vs)

The above seems to suggest that DAC is not sending any red and the low signal on green. The fact that R, G, and B inputs seem to be uniform in terms of signal for white and black screens suggests the DAC is being sent reasonable values.

Sounds like it might be the DAC that is not doing well. I guess I need to find and try a replacement? So either an ADV473 or a BT473?

 

[MacOSMonkey]

Sounds like it might be the DAC that is not doing well. I guess I need to find and try a replacement? So either an ADV473 or a BT473?

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. But, Analog Device's mission was to compete with Brooktree in every application setting. I think they are the same, but you would have to check to be absolutely sure.

 

[MacOSMonkey]

Reflowed the entire 24/III main board (and the daughter card again). So far it's holding up after a cold boot. Hope it sticks this time..

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.

 

[jmacz]

Here's the data sheet for the BT473.

Looks like it's a match? But I think I'm seeing two variants, a BT473KPJ-110 and a BT473KPJ-110ES2. Not sure what the difference is.

For the ADV, the part is ADV473KP110ES. Found a few places in the US that sell components but not clear whether they only sell to businesses or with huge minimum quantities.

 

[MacOSMonkey]

Here's the data sheet for the BT473.

Looks like it's a match? But I think I'm seeing two variants, a BT473KPJ-110 and a BT473KPJ-110ES2. Not sure what the difference is.

For the ADV, the part is ADV473KP110ES. Found a few places in the US that sell components but not clear whether they only sell to businesses or with huge minimum quantities.

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 J-lead (on the PLCC package)
The number is the speed. Don't use anything lower than a -110. Higher, like -135, may be OK -- but identical drop-in is safest.
ES is probably the rev level, or ES1 -- use the same rev level. There may be application changes between different ES revs. An ES2 might not work in place of an ES (ES1 implied). I don't know.

Also, in the ADV datasheet, there is an interesting note that may relate to the problem you are seeing and my earlier comment:

"ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily accumulate on the human body and test equipment and can discharge without detection. Although the ADV473 features proprietary ESD protection circuitry, permanent damage may occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended to avoid performance degradation or loss of functionality."

Good luck -- assuming it's the ADV473, you should be able to find a part.

 

[jmacz]

Thanks for your help @MacOSMonkey !

 

[jmacz]

Finally making some progress on procuring a replacement RAMDAC. Probably went overboard here but I've got a BT473KPJ110 on its way from Europe (thanks @Phipli for the pointer!) and I found a US distributor that was willing to sell me a single BT473KPJ110ES2 and that's also on the way (that's the only variant they had so I took a chance -- this was before I was able to secure the other non-ES2 chip). Also finally found another distributor today that has a US office (but I think it's still a Chinese company) that seems to have the ADV473KP110ES and is willing to sell it to me. Still working on a quote. So I guess I will try the ADV473KP110ES first as that's the direct replacement. If that doesn't work or is a fake chip, I will move on to the BT473KPJ110 and as a last resort I will have the BT473KPJ110ES2. Hopefully one of these works. And also importantly, replacing it fixes this card.

 

[MacOSMonkey]

@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!

 

[jmacz]

Well, doesn't look like the BT ES2 works. The card won't even detect. Checked all the solder joints and they are all good. I thought I may have messed something up so took it off and put the original ADV back in and that will get the card to detect and come up with the same blue tinted video issue. So doesn't look like the ES2 is fully compatible or something's going on. Will try the others once I receive them.

In the meantime, I think I may have found a few surface mounted capacitors and transistors that are bad. I'm getting suspect measurements from them via my multimeter. There's about 5 or so of them in the vicinity of the previous burnt fuse. Rest on the board return reasonable numbers.

Anyone know how to determine the specs of these surface mounted caps/transistors? They are using 1206 packages, but not sure how you're supposed to determine the specs as there are not distinguishable markings on them.

 

[MacOSMonkey]

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 risk for delamination/lifting/tearing off - especially if tweaked during part removal (and excess heat/duration). Small pad geometries generally translate to less FR4 adhesion strength. Trace/pad repair can be challenging, as you might imagine. Anyway, you probably know all this stuff - just advising caution. Good luck!

 

[jmacz]

If the cap is completely shot, measuring them after removing them won't work either right?

Thanks for the reminder on the repeated rework. Only removed the DAC twice so far and being extra careful.. hoping no issues if I have to try it two more times. That said, with the damage on the board, I was able to talk to the seller and get this card for a very low price and was just hoping to see if I can repair it. If not, that's ok. The price was already worth it for the learning process.

As for the 24/III, it's rock solid now with the last reflowing of the board which is great.

 

[MacOSMonkey]

Correct - if you remove the cap from the board, you should be able to tell if it is good or blown/shorted. Also, there are a zillion web guides.
re: Spec/24 III - great! You should be good to go, since you have the v1.1 ROM.

 

[Phipli]

Correct - if you remove the cap from the board, you should be able to tell if it is good or blown/shorted. Also, there are a zillion web guides.
re: Spec/24 III - great! You should be good to go, since you have the v1.1 ROM.

I think they mean that if it isn't labeled and also is a failed part, they can't tell what value to replace it with.