If your MPU is only getting 6 flashes, that means the 43v is too low or missing. Here's a copy of the manual: https://www.ipdb.org/files/698/Bally_1979_Dolly_Parton_Installation_and_General_Game_Operating_Instructions_with_paginated_schematics.pdf
A great place to start is Pinwiki, they have a general repair section, and game generation-specific pages: https://www.pinwiki.com/wiki/index.php?title=Bally/Stern

Check test point 5 on the rectifier board (right side of the head above the transformer), it should be 43vDC.

^^^^ this

If that's a keeper and it sounds like it is, you might want to spend $167 delivered on a new MPU if your budget allows that. Board connectors are an issue on early Bally SS games but from your description of the issue that may not be the case.

https://nvram.weebly.com/mpu.html

True. But, this very well could be coming from the old rectifier board next to the transformer. It's great place to start.

Over-used BRs/fuse clips/headerpins. New rectifiers are around $100 and have screw in terminals so you don't have to re-solder.

Then, the MPU header pins and connectors, plus MPU are also suspect.

Very simple to check the rectifier with a DMM.

New rectifier boards no soldering and work great:

https://xpinpinball.net/product/xp-bly2518-ebr/

If you bought it as working from a collector, I would hold off on replacing boards. Your rectifier board looks very fixable, and new MPU is a great idea in most cases but if it was working up to this point, sounds like it isn't necessary.

Check underneath the playfield for a inline fuse mounted to the playfield itself. Seems like it could keep the game down as well but it's been years.

John

holy cow, lets slow down a step. Do not start spending money unless its on a multimeter. Follow the pinwiki and do some investigation. old bally games are easy. Follow the power from the plug in the wall to the mpu. As stated more than likely its going to be the rectifier board. Check the fuses then use the multimeter and check the voltage on the test points. If everything is good there, move over to the MPU and make sure you have the required voltage on test point 3 (21.3 ish). Thats pretty much what you need to get the 7th flash. Anything more and then I would see about getting someone to help out.

Throwing boards at problems without doing some cursory trouble shooting is an expensive and ineffective way to get your game going.

First is to insure you count the flashes correctly. The proper sequence is there should be a quick flicker, a flash, pause, then 6 more flashes.
A missing 7th flash indicates the 43v coil voltage is missing. In most cases that means the 5amp fuse, F4 on the rectifier board, has blown. This is such a common problem, even if the fuse visually looks good you should check it with a multimeter to be sure. If the fuse tests good measure the voltage at the MPU. J4-15 should have 43v and TP3 should measure 21v. If all these check out good only then you should consider board work.

If you have the 44 volts then your problem is more then likely a connection at probably the driver board or the MPU board. Reseat the connectors and try again. Or you could have cold solder joints....

John

While your CPU looks quite nice, it has some battery damage near the negative side of "no leak" battery - probably due to the previously installed nicad.

Try resoldering all greyish connections. Also surprisingly often the display interrupt generator U12 or some of its surrounding components fail - that might be causing the board to miss the zero cross interrupt from unreg 43V. First try replacing C16, then U12.

If you have a scope or logic probe, check for about 300 Hz at U12 pin 3 - exact value is not critical.

Check test point 3 on the MPU. bottom left corner and see if the voltage is getting there. if it is, you have a board problem, if not you have a wiring/connector/header problem

Health comes first, pinball can wait. Wishing you a speedy recovery

R113 and R16 is a 50% voltage divide on the 43v for the zero cross detection (flash 7). Someone replace R113 but not R16 which is suspect (and kind of goofy). Those resistors are a typical failure point. Use half watt resistors there. If R16 goes totally open it is possible to smoke U8 as the voltage may double(?). Check MPU Test Point 3 and consider replacing R16 with the same value as R113 (half watt resistor, probably 2K).

You also left out a picture of your solenoid driver board. 13v is usually a little low and may be an indication the filter cap is failing. With the large capacitor on the driver board the 12v usually comes up to around 16-17v (11.9v x 1.4).
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