ESQ-1 5V-related issues

Hey everyone, I just bought an ESQ-1 for dirt cheap that’s got some issues. It was putting out sound (not anymore… I pulled the CPU and no sound after resocketing. Stupid of me…), but it’s got some display issues like many ESQ-1s.

The main symptoms are a blank display and unresponsive buttons, which immediately tell me I need to replace the display controller (maybe with Buchty’s custom one). Easy.

I am worried about the display itself, as there are some black marks under the glass right where +/-VAC come in to the display. Any way to test for a working display without a working display controller?

The last thing is that the 5v supply measures out of spec under load, 4.6V to be exact. It measures the same with main+display boards plugged in as well as each separately. Is this low enough to worry about? If so, how can I go about finding the cause of the droop?

Thanks everyone!

The first issue i would look at is the 5V supply. The voltage from the supply is too low for reliable operation. This will affect the display and main board logic circuits.
The 5V regulator is a fairly rugged device that will protect itself from overload and overheating.
In order for the 5V regulator to run reliably the device needs at least 2 volts higher on the input to maintain a constant output voltage. So you should be seeing at least 7 volts feeding the input of the regulator (7805). If you’re not getting the required voltage (7V) then you need to look at the filter capacitors, rectifier diodes, or transformer secondary voltage. The schematics and service manual are available online.
One other thing to check is the thermal paste on the voltage regulator. It tends to harden and lose its thermal conductivity after all these years.
Good luck with the repair!

1 Like