1980s_john
Experienced Member
Hi,
Quick summary - no issues found powers up with all the expected voltages under load.
I have a stack of 3 PC-8001 units all with the same power supply. I have never powered these units on, so I thought I would go through and check them over before doing so (as a faulty PSU can damage an otherwise perfectly good unit). I started with a PC-8031 (actually PC-8031BE for european 230V), the power supply unscrews quite easily, it is a BYG340/ 42K model made by Shindengen of Japan who are still going strong. I unscrewed the PSU (black painted metal case with vent holes), PCB was in good condition with no leaking / burnt components. Dated 1981. I checked over all the Elna brand electrolytic capacitors with an LCR meter, all measured fine as follows which is amazing for a 38 year old unit (must have been powered off for nearly all that time).
Capacitors were marked and measured in circuit as follows (at 1kHz), all well within spec.
C08-1 47uF 400V.
C08-2 47uF 400V. In parallel with C08-1, measured 107uF 0.4 ohm.
C13 100uF 25V
C14 100uF 25V. Both measured 90uF 0.3ohm.
C17 3300uF 10V
C18-1 220uF 10V
C18-2 2200uF 10V. C17/C18-1/C18-2 all in parallel, measured 11000uF.
C19 2200uF 10V. Connected to above via filter coil and resistor, measured 18000uF. Measurement not stable, looked OK, didn't unsolder to do any accurate measurements.
C20 470uF 25V. Measured 450uF 0.1 ohm.
C21 100uF 25V. Measured 97uF.
C22 1000uF 35V
C23-1 1000uF 35V
C23-2 1000uF 35V. C22/C23-1/C23-2 all in parallel, measured 3400uF.
As above showed no issues I decided to power on at 230V with a 10ohm 10W load across the red/black output (see below for voltages). I didn't bother with variac or series light bulb (feeling brave).
Powered on and no smoke / bangs, 12V measured across load so looked good. The output lead is to a multi-pin socket, the voltages measured on each pin were as follows:
Black 0V
Yellow +5V
Pink +12V
Blue -5V
Red +12V (pink and red are commoned).
So no issues with this PSU, a really well made unit! I will load up the 5V output too as a test first before connecting it to the PCB but I don't expect any problems.
I will check out the hopefully identical PSUs in my other two similar units (PC8012 and PC-8032) and report back any differences. I'll start a new thread on the PC-8031 PCB and drives, the PCB in this unit contains a FDC chip and some RAM plus some dreaded tantalum capacitors so plenty to look into.
Here's my webpage on the system:
http://vintagecomputers.site90.net/nec/
Regards,
John
Quick summary - no issues found powers up with all the expected voltages under load.
I have a stack of 3 PC-8001 units all with the same power supply. I have never powered these units on, so I thought I would go through and check them over before doing so (as a faulty PSU can damage an otherwise perfectly good unit). I started with a PC-8031 (actually PC-8031BE for european 230V), the power supply unscrews quite easily, it is a BYG340/ 42K model made by Shindengen of Japan who are still going strong. I unscrewed the PSU (black painted metal case with vent holes), PCB was in good condition with no leaking / burnt components. Dated 1981. I checked over all the Elna brand electrolytic capacitors with an LCR meter, all measured fine as follows which is amazing for a 38 year old unit (must have been powered off for nearly all that time).
Capacitors were marked and measured in circuit as follows (at 1kHz), all well within spec.
C08-1 47uF 400V.
C08-2 47uF 400V. In parallel with C08-1, measured 107uF 0.4 ohm.
C13 100uF 25V
C14 100uF 25V. Both measured 90uF 0.3ohm.
C17 3300uF 10V
C18-1 220uF 10V
C18-2 2200uF 10V. C17/C18-1/C18-2 all in parallel, measured 11000uF.
C19 2200uF 10V. Connected to above via filter coil and resistor, measured 18000uF. Measurement not stable, looked OK, didn't unsolder to do any accurate measurements.
C20 470uF 25V. Measured 450uF 0.1 ohm.
C21 100uF 25V. Measured 97uF.
C22 1000uF 35V
C23-1 1000uF 35V
C23-2 1000uF 35V. C22/C23-1/C23-2 all in parallel, measured 3400uF.
As above showed no issues I decided to power on at 230V with a 10ohm 10W load across the red/black output (see below for voltages). I didn't bother with variac or series light bulb (feeling brave).
Powered on and no smoke / bangs, 12V measured across load so looked good. The output lead is to a multi-pin socket, the voltages measured on each pin were as follows:
Black 0V
Yellow +5V
Pink +12V
Blue -5V
Red +12V (pink and red are commoned).
So no issues with this PSU, a really well made unit! I will load up the 5V output too as a test first before connecting it to the PCB but I don't expect any problems.
I will check out the hopefully identical PSUs in my other two similar units (PC8012 and PC-8032) and report back any differences. I'll start a new thread on the PC-8031 PCB and drives, the PCB in this unit contains a FDC chip and some RAM plus some dreaded tantalum capacitors so plenty to look into.
Here's my webpage on the system:
http://vintagecomputers.site90.net/nec/
Regards,
John