Is there a way to test in circuit if a chip is broken or not using a
multimer or some_other_instrument_lot_cheaper_than_osciloscope ?
Measuring temperature of chip while it has been working for a while
should be indicative, but how?

"orange" wrote in message
ups.com...
Is there a way to test in circuit if a chip is broken or not using a
multimer or some_other_instrument_lot_cheaper_than_osciloscope ?
Measuring temperature of chip while it has been working for a while
should be indicative, but how?


It depends on the chip. If it's a digital IC (e.g., logic gate), a simple
and inexpensive logic probe can tell u what u need to know. If, however,
it's a complex circuit -- such as a video processor -- you often need to
look at the waveforms. You can certainly test for proper voltages on the
pins, but that doesn't always tell u what u need to know. Sometimes ya
gotta pay to play.

"orange" wrote in message
ups.com...
Is there a way to test in circuit if a chip is broken or not using a
multimer or some_other_instrument_lot_cheaper_than_osciloscope ?
Measuring temperature of chip while it has been working for a while
should be indicative, but how?


Some chips run surprisingly hot, so unless it gets hot enough to split the
casing there's no guarantee this indicates a fault.

All the test gear in the world won't tell you if a chip is faulty if you
don't know what its supposed to do - and none of us do either because you
didn't tell us!

OK, I understand.
its a broken computer, Amiga 1200, it displays for a second blue screen
(which means one of custom chips is broken) and then black screen with
faint parallel stripes.

"orange" wrote in message
oups.com...
OK, I understand.
its a broken computer, Amiga 1200, it displays for a second blue screen
(which means one of custom chips is broken) and then black screen with
faint parallel stripes.


The faint stripes could indicate HF ripple from the PSU, maybe crashing one
of the chips. In this case overheating capacitors in the PSU might be a
better clue!

In the past when servicing PC monitors, I have used my sense of touch to
test for overheating electrolytics but BEWARE! the can of the capacitors is
not isolated and so the mains reservoir cap on the primary side will have a
large voltage on it! So make sure you can distinguish between primary &
secondary parts of the PSU before poking your fingers in!!!

In any event while inspecting/testing live equipment correct safety practice
is absolutely vital - wear rubber soled shoes, make sure you're not touching
anything earthed (chair next to a radiator?!!!) and keep one hand in your
pocket so if you do touch a live part - you don't give it a path to earth
via your chest!

Some engineers deal with this type of PSU by simply replacing all the
electrolytics and making sure all the new replacements are good quality 105
DEG-C types to ensure future reliability. IIRC - the Amiga PSU has a small
1uF 50V electrolytic that dries up and causes the PSU to radiate RF noise!

thanks for the reply, but its not PSU for sure.
I've used ordinary PC AT power supply that is tested and works with
other Amigas.
one nice day I'll buy osciloscope and one nice year learn to use it

thanks for the reply, but its not PSU for sure.
I've used ordinary PC AT power supply that is tested and works with
other Amigas.
one nice day I'll buy osciloscope and one nice year learn to use it
properly

Hello orange,

orange wrote:

OK, I understand.
its a broken computer, Amiga 1200, it displays for a second blue screen
(which means one of custom chips is broken) and then black screen with
faint parallel stripes.

Amigas have very common faults. I'd give it a try to search Google
for a A1200 fault database. Also the guys on www.amiga.org are
quite into Amiga hardware (what a surprise ). The biggest
problem about repair is that none of the large chips on the
1200' board are socketed anymore as opposed to the 500/2000
which will replacement much more difficult.

Adrian