Broken Vectrex

[moycon]

Unfortunately, the last time I went to turn on my Vectrex it wouldn't boot up and nothing I tried would remedy the situation.

I could tell it was powering on but only a small dot would appear, and no sound,

Too many moves over the years I guess. Sucks because I really enjoyed it. Is there any type of troubleshooting guide or does anyone in the community repair broken Vectrex systems?

[MattPilz]

I've been diving deep into Vectrex repairs of my own this past month and they can be really fragile machines. The white dot is a classic symptom, if the system malfunctions and isn't able to output XYZ it'll shut off the screen except on super bright to prevent burn-in. No sound or video output could be indicative of a bad ROM/CPU/RAM combo, but from my experience is more likely a voltage disruption along the path...

 

So the first thing to check would be voltages. If you are comfortable opening it up and probing around with a multimeter, these would be my go-to checks (from memory) and I'd be interested in knowing your findings:

• Three wires connect to the side of the power board from the power switch / secondary winding of transformer. They are usually BROWN - WHITE - BROWN with white being the common. Next to those is a short, thick ground wire connecting the power board to the logic board. In AC voltage if you put ground probe on WHITE and red probe first to check one BROWN then the other, both sides should be roughly equal and somewhere between 8-12V. If only one side has a reading, the culprit is likely the power/volume switch (much less likely to be the transformer). These are prone to failure and corrosion and can result in only half the power getting where it needs to. Sometimes Deoxit F5 or D5 can help.
• Four wires that run from the power board to a plug (J204) on the logic board. The black wire is ground, the other ones should have DC voltage readings of -5V, 5V, -13V. If you unplug the end and put one probe into the BLACK wire, then test the other three wires and find there is something missing, then the problem lies in your power board itself. If you get the correct power, plug it back in and carefully check on the underside of the logic board for those four pins to rule out any corrosion, dry solder joints etc. that may be causing it not to reach the rest of the logic board when plugged in.
• IC101 Voltage Regulator (LM340) - The output pin on the power board should read +5VDC.
• IC102 Negative Voltage Regulator (LM7905) - The output in on the power board should read -5VDC.
• IC301 DAC (MC1408) Pin 3 - This should be -13DC. 

From there it gets more complicated to troubleshoot if there aren't any obvious voltage losses. I had similar symptoms here and there and in my case one of the two voltage regulators had shorted, but at another point it was a problem with Q502 power transistor (BU407D). It becomes easier to troubleshoot if you get sound again since that indicates the CPU, RAM and ROM are all functional (as well as AY chip, generally).

 

There are three valuable resources for continued troubleshooting:

 

• Original Service Manual - https://console5.com/wiki/File:Vectrex-Service_Manual.pdf
• Original Troubleshooting Guide - https://console5.com/wiki/File:Vectrex-Troubleshooting_Guide.pdf
• Brand New Detailed Guide with Oscilloscope Patterns to Check and Alternate Schematics - https://github.com/Guimli/Vectrex-Repair-Manual/blob/main/Repair manual Vectrex 20220613.pdf

Good luck...

Edited July 7, 2022 by MattPilz

[SeeOne]

If you get the white dot, no sound, AND NO VECTOR "CHATTER" it means the MPU, PIA, and Memory are not working together correctly.

 

1. check voltages as specified above

2. If that is working, chances are it is the PIA chip (6522) -- and it should be replaced.

 

Good Luck :)