29-01-2021, 06:43 PM
(This post was last modified: 02-02-2021, 03:10 PM by someone.
Edit Reason: Clarification upon transition to DC input voltage
)
Welcome aboard Lew!
Someone is also also a ham and is happy to help you get the microbees up and going again.
Just send someone a PM and we can exchange callsigns.
The metal based microbee is the most interesting. Do you know what BASIC revision is written or printed on the ROMS?
They might range between 4.9x to 5.00 Are they ceramic purple Hitachi ROMs by any chance?
The metal based microbee runs on about 10VAC @ 50Hz. Back then, plug packs read higher open circuit voltages than when under load.
The TO-3 regulator is rated at 1.5A. AC was used so that a -12V voltage source could be used on the RS232 signals.
Subsequent models used 10VDC after finding out that most RS232 equipment worked without the negative voltage swing (i.e. +10V to near 0V transition was sufficient). The change from AC to DC also remedied many 50Hz AC hum issues.
The 3 x 1.5AA batteries replaces the original 4.5V camera battery.
Just ensure that the voltage past the rectifier diodes reads a voltage higher than the dropout voltage of the 7805/LM309K voltage regulator and microbee power good sensing circuit.
If you've got an oscilloscope it'll make things much easier to fix.
(Back in the 1970's to early 1980's owning an oscilloscope with sufficient was just a dream. - Someone didn't have the dosh to afford a 60-100MHz one).
It also pays to use the probes correctly so that you're not seeing distorted signals.
73's
Someone is also also a ham and is happy to help you get the microbees up and going again.
Just send someone a PM and we can exchange callsigns.
The metal based microbee is the most interesting. Do you know what BASIC revision is written or printed on the ROMS?
They might range between 4.9x to 5.00 Are they ceramic purple Hitachi ROMs by any chance?
The metal based microbee runs on about 10VAC @ 50Hz. Back then, plug packs read higher open circuit voltages than when under load.
The TO-3 regulator is rated at 1.5A. AC was used so that a -12V voltage source could be used on the RS232 signals.
Subsequent models used 10VDC after finding out that most RS232 equipment worked without the negative voltage swing (i.e. +10V to near 0V transition was sufficient). The change from AC to DC also remedied many 50Hz AC hum issues.
The 3 x 1.5AA batteries replaces the original 4.5V camera battery.
Just ensure that the voltage past the rectifier diodes reads a voltage higher than the dropout voltage of the 7805/LM309K voltage regulator and microbee power good sensing circuit.
If you've got an oscilloscope it'll make things much easier to fix.
(Back in the 1970's to early 1980's owning an oscilloscope with sufficient was just a dream. - Someone didn't have the dosh to afford a 60-100MHz one).
It also pays to use the probes correctly so that you're not seeing distorted signals.
73's