Question About Circuit Testing

[hugh1097]

Hi,

So i think I may have bitten off more than I can chew in building a GSSL clone...

My main (noob) question is, is there any way to begin testing the PCB without hooking it directly up to AC?

Can I bypass the transformer section using test equipment(if so what would i need)? Are there any tutorials out there for this type of thing?

Thanks muchly!

 

[David Kulka]

If you had a bench power supply or two you could connect them (bypassing the transformer) and gradually increase voltage while monitoring current, as a safe method of first power up.

Similarly, if you had a AC line variac you could could power up the the unit and gradually increase voltage while monitoring current.

I often use those one of those methods when I'm concerned about short or other problems, and don't want to power up with full voltage in my initial tests.

 

[Gene Pink]

Similarly, if you had a AC line variac you could could power up the the unit and gradually increase voltage while monitoring current.

In my humble opinion, anyone messing with electronics on any level including newbie, needs four things to successfully get started:

1) Common sense

2) A digital multi-meter / VOM / VTVM / wet finger and experienced tongue

3) Soldering iron / Weller gun / butane torch / thermite

4***) A Variac / Powerstat / serious lighting dimmer that doesn't freak out with inductive/reactive loads.

*** a poor mains variac substitute can be as simple as a light bulb in series with the DUT (device under test).

Take a cheap-ass short extension cord, cut into the sheath in the middle to expose the wires within, cut the black (brown) wire, and connect both ends to a light bulb socket.  Have a selection of various wattage incandescent bulbs, no CFs, no LEDs, just good old fashioned edison-invented tungsten-filimented GE soft-white bulbs.  Start with the 15 watt one, work your way up, paying attention to the bulb brightness as in indication of load  current. It does take a bit to get a feel for what brightness level is good or bad, depending on the expected draw of the DUT.

An enhancement on the above: A toggle switch from after the light bulb socket to neutral. With the switch closed, the light is fully on. THe DUT is connected and on, open the bulb switch, and a nice, gentle ramp up of current in the DUT. This avoids the DUT dealing with the surge of powering up a cold light bulb, where the current can be 10 times the hot current.

For what it is worth,
Gene

 

[Michael Tibes]

I'd  start testing by pulling all the integrated circuits apart from the psu (hopefully they have sockets), powering it up and checking the supply voltages in all possible spots. Before that triple check all electrolytics, tantals and diodes for correct polarity. I'm not sure how useful a variac would be unless there's really something horribly wrong. To be very safe you could also unsolder the mains transformer outputs first and check for the correct ac voltage (probably a bit higher than what it should be without a load) when you turn it on so you're sure that there's no fault in the mains wiring. To be super safe you could then insert the ics one by one (obviously turn it off after each test) and look for smoke.

Michael

 

[hugh1097]

Thanks for the replies guys. A lot of useful info here!

 

[JohnRoberts]

Similarly, if you had a AC line variac you could could power up the the unit and gradually increase voltage while monitoring current.

In my humble opinion, anyone messing with electronics on any level including newbie, needs four things to successfully get started:

1) Common sense

2) A digital multi-meter / VOM / VTVM / wet finger and experienced tongue

3) Soldering iron / Weller gun / butane torch / thermite

4***) A Variac / Powerstat / serious lighting dimmer that doesn't freak out with inductive/reactive loads.

*** a poor mains variac substitute can be as simple as a light bulb in series with the DUT (device under test).

Take a cheap-ass short extension cord, cut into the sheath in the middle to expose the wires within, cut the black (brown) wire, and connect both ends to a light bulb socket.  Have a selection of various wattage incandescent bulbs, no CFs, no LEDs, just good old fashioned edison-invented tungsten-filimented GE soft-white bulbs.  Start with the 15 watt one, work your way up, paying attention to the bulb brightness as in indication of load  current. It does take a bit to get a feel for what brightness level is good or bad, depending on the expected draw of the DUT.

An enhancement on the above: A toggle switch from after the light bulb socket to neutral. With the switch closed, the light is fully on. THe DUT is connected and on, open the bulb switch, and a nice, gentle ramp up of current in the DUT. This avoids the DUT dealing with the surge of powering up a cold light bulb, where the current can be 10 times the hot current.

For what it is worth,
Gene

Yup we used to call them "load boxes" (Variac with series light bulb to current limit, and bypass switch.) and they were the only way to repair power amps.

JR

 

[Whoops]

Common sense


a poor mains variac substitute can be as simple as a light bulb in series with the DUT (device under test).

Common sense


1) triple check all electrolytics, tantals and diodes for correct polarity.

2) To be very safe you could also unsolder the mains transformer outputs first and check for the correct ac voltage  (probably a bit higher than what it should be without a load)

3) I'd  start testing by pulling all the integrated circuits apart from the psu (hopefully they have sockets), powering it up with a a poor mains variac substitute (can be as simple as a light bulb in series with the DUT (device under test)), and checking the supply voltages in all possible spots.