Friend given a Revox open reel and Tascam 4 track - suggestions be we power them up?

A friend was given 2 older open reel decks and thought I’d ask what to do before powering them up and testing?

The only open reel tapes I have to test with are masters (I want to transfer to digital, but I imagine it wouldn’t be a good idea to try them on the deck before we know it’s working properly.

Any suggestions where to get them refurbished in the NYC area?

any idea what they are worth once refurbished? I’m trying to convince him it might be worthwhile to invest some money.
a real tune up on either will start at $300. Do Not risk a master on either. Buy a prerecorded tape at a used music store , NYC ….to check…..

Listen to tomic, not to fuzztone. Both decks are worth restoring if they work. Check eBay for prices and I have parted them out for good money too. Get a pre-recorded tape to test, don't use the masters.
If not run in some time, should be powered up with variac. Caps could be dried out, may need reforming. If diy, capacitor kits sold at various vendors.
Thanks for all the tips.  I don’t have access to a variac, as they haven’t been needed for film production for a long time.  Wondering if there is a modern smaller solution.  
a low voltage brownout day…

@bigkidz might be able to help, but don't expect free.
Don’t worry about a variac, just turn it on. This is not vintage tube gear. No large old caps in there to dry out. I fire them all the time without a variac and I have one.
@dill thanks - I found a place in NYC that does a cleaning and alignment for $350 and hopefully not too much will be needed in repairs.

I’m super excited to hear masters I recorded decades ago in blumlein.

The Revox is an a77 mk IV (we think it’s a MK IV)