Thought I would update this post on my progress for anyone interested.
I replaced the LM393 and the nearby failed NMOSFET. My handy work is attached.

The unit turned on with no magic smoke. I recently purchased the DMMcheck Plus so I was using that to determine if the meter was operating correctly, It was not. DC voltage measurements were off by about 2 orders of magnitude and resistance/ACV voltages were not responding. Surprisingly the DC current was measuring correctly. I got smart and looked up how the analog circuitry operates in the service manual, figure 4-3.

Following that diagram I could focus on the parts that deal with the voltage/current/resistance/frequency measurements. I also got even smarter and pulled out my Seek thermal camera and had a look around. I found a few more damaged components. Below is a list of additional components I have replaced, most of them were truly damaged.
- U105 and nearby U103: DG211DY CMOS analog switch
- U115: LM393 quad comparator
- U102 and U118: TLE2081CD J-FET Op-Amp
- Various SNJ132199 JFETS that are shown in figure 4-3
- I also replaced all the electrolytic caps after observing a few of them getting uncomfortably warm
To make a long story short the unit now is able to measure DC voltage correctly along with resistances below about 1Kohm. DC current works too.
I still have a few more repairs to try to fix AC voltage measurements and enable the full range of resistances. Looking at figure 4-3 I'm planning on replacing U123, Q124 and Q125 to repair the ohms current source. A few rough measurements using another multimeter of the resistance current suggested that this may be the issue.
For the AC voltage I have U112 on order but it was not in stock through Digikey so hopefully eBay will pull through and get me functioning products.
Guess this can be considered a partial repair for now. That shit faced grin has returned to my face after restoring the ability to measure DC voltage.
