Eventide H969

[Polyphemus]

My 969 has been moody for many years, which generally was fixable by reseating the ic's in their sockets.
Now it's dead. Direct sound stillcomes through and the display and controls react as the should. I've inspected the boards and found 2 (maybe 3) dead components.
Does anyone by chance have a schematic (long shot), or is there anyone who might have a 969 and could measure the components? It's two resistors and another component which possibly might be a miniature fuse.
It's on the RB224 and RV 228 boards (rev. E). Pictures are (hopefully) attached.
In the first picture its the two clearly burned resistors, of which one might be something else, in the second picture its the resistor surrounded by the lf356,big tantalum and connector/0.1 cap.
Thanks in advance for your help.

 

[Polyphemus]

Pic 1

 

[Polyphemus]

Pic 2

 

[Khron]

What're the odds the toasted resistors are in series with some power rails, where some of those bead tantalum caps might've shorted out?

 

[Polyphemus]

I'm assuming the odds are rather high. They are on the line for replacement already.

 

[Khron]

I've "even" seen chip (SMD) tantalums kick the bucket, like in an Apogee Ensemble i fixed last winter (took out the negative supply for the ch1/2 preamps).

https://khronscave.blogspot.com/2019/11/57-apogee-ensemble-firewire-pt2-repair.html

 

[Polyphemus]

Well one of the rails is definitely shorted to ground, so there's one fault. The toasted on the other board is also in some kind of relation to a tantalum which reads in the low ohm range, so cause of meltdown might be found. Now I only need to figure out the value of the burnt resistors.
I'm going to desolder and see if I can measure any resistance.

 

[Polyphemus]

Both resistors one the first board are in series with their respective rail, so I assume they would have the same resistance. The one not completely obliterated measures 10k, which lets me assume that the other would be of the same value.

 

[Khron]

"The one not completely obliterated"... is connected where?

Just because they're next to each other, doesn't necessarily mean they play similar roles in the circuit. Not to mention, 10k's an awful high value to have in series with a power rail. Unless it's connected between that rail and ground, as a minimum load / cap discharge resistor.

 

[Polyphemus]

They are connected in following fashion:

 

[Polyphemus]

If my colorblindness doesn't impede my reasoning, the resistor colours are brown, black, black, which should amount to 10 ohm. Probably a more reasonable value for a series resistor.

 

[Khron]

If that's 10k, that's toasted too. If it were something like 10 ohms, that would be a lot more realistic indeed.

Is the rail with the "10k" on it, going to pin 14 of that 74C32?

PS: Don't worry, i have trouble distinguishing between brown and black, or brown and red, on through-hole resistors ;D Depending on what tone of brown the manufacturer had that day...

 

[Polyphemus]

Funnily enough both junctions between resistor and capacitor end blind on the board.. they would have supplied an 8pin dip, if it were fitted.

 

[Khron]

Well, if the other toasted resistor connects to a tantalum, it's a reasonably safe bet that's 10 ohms too.

If you get bored, feel free to measure the resistance across those tantalums before and after removing them (on the board, i mean)

But yes, blanket-replacing them is a safe bet - if those first few started crapping out now, the others will follow...

 

[Polyphemus]

Yeah I figure it's time for those kinds of measures. 
Thanks for your help! I think I can figure it out now. Hopefully it didn't take down any of the esoteric ic's on the board.

 

[Khron]

I doubt it - if tants on the supply rails shorted to ground, they just dragged the respective rails down until those series resistors blew, and that's that.

Absolute worst case, some of the voltage regulators might've had a harder-than-needed life, but if you're reading "sane" voltages "before" the blown resistors, all should be well. After a re-cap, of course