Arcam Alpha 9 - Help Needed

[danza]

Hi all,

I've just received a faulty Alpha 9, and upon testing, I've found the following:

• Upon powering on, the display illuminates, allowing apparent track selection (no laser movement at all)
• There's a quiet high-pitched whining from the transformer/surrounding area
• The disc spins up and stops after a few seconds
• The laser does not move at all from the idle position at the outer edge of the disc.
• There is discolouration to the casing above the tranny, to the casing and the DAC mounting
• The PCB around Z204 &205 is discoloured as pictured
• The metal part of Z207 is slightly discoloured
• Resistor R44 is a bit burnt. Inout 31V, output 5V
• Caps C44,4 & 48 sligthly bulging.

I'm able to use an Avo, have access to an oscilloscope, but don't know how to use it. How would I check if the tranny is dead? Does anyone know the voltages coming from the tranny?

Any suggestions as to what i could try would be brilliantly useful!

Dan

[Mooly]

The transformer won't be dead if it all lights up.
You need to see a circuit. R44 is duff... it looks like a safety resistor and will be low value. I would guess at less than 4.7 ohms but would have to see circuit to be sure. What does it measure out of circuit ? is it OC ?

Looking at the circuit will reveal all... just guessing otherwise.

I would check those 4 diodes, see where that resistor goes and what it feeds, and check those two power devices... are they regulators ? looks like they run hot from the discolouration of the PCB. And those caps too of course.

[danza]

Cheers for your reply.

I haven't checked the resistor for OC, didn't think to. I'm not really sure how to check diodes or the transistor, can you enlighten me?

I'll email Arcam later and get a diagrams from them.

[danza]

Also, I'm hoping the DAC board isn't grenaded!

[danza]

Right, I've emailed Arcam requesting the service manual.

The resistor R44 is not OC, and with my attempt at using the Avo to measure out of circuit, it seemed about 16K (does that seem right?). Suffice to say it'll be changed when I get the service manual and know what it was.

[Mooly]

This is another thread that didn't notify of your replies must ask about that.

16k. First you can not measure in circuit as a general rule. Any residual charge (only a few milli volts) totally confuses the readings on a meter.
With that proviso, low value resistors can usually be measured OK in situ because by definition they won't have any voltage across them when the power is off... certainly not after a second or two.
So 16k is duff. You couldn't get enough power from the low voltage side on the player to burn out a 16k resistor. You would need around 250 volts plus to burn a 16k like that
That resistor should be around 0.1 to 4.7 ohms at a guess.

Measuring transistors and diodes on an AVO is different to a DVM. The polarity of the leads is reversed when you put an AVO on ohms, the red lead becoming negative and the black positive.
As a simple check, with the AVO on low ohms (times 1) and the black lead on the anode of a diode (the NON stripy end) and the red on the other (cathode) it should read. Reverse the leads and it should not. However stray circuit reistance from other components will affect the readings.

I would recommend you read up (google) how to check transistors etc and remember that for the AVO the readings (meter leads) are the opposite of what will be described.

When you see a circuit it should be more obvious what has failed and why.

Edit... I'm assuming your AVO is a "swinging brick" an AVO 8

[danza]

LOL, "swinging brick".

Yeah, it's that type. I've bought a DVM for my own use - one with transistor/diode check. The Avo belongs to my employer. We do barely any electrical work, so it's all we need, if slightly hefty.

I'll post up circuit diagrams as soon as I hear from Arcam.

Cheers

[Mooly]

OK then
Actually AVO's are great for checking semiconductors (once you are used to them) as the 10,000 ohms range uses a 15 volt battery and that can show up leaky junctions etc... but exercise caution, it can also damage sensitive IC's etc.

[coolmaster]

Some hints:
1. R44 is 3R3ohm Fusable resistor
2. Replace those bulging caps, might as well all 4 of them. Bulging caps are likely shorted internally.
3. Those regulator IC's could be faulty or shorted. Replace them.
Good luck!

[Ecaroh]

Originally Posted by danza

I haven't checked the resistor for OC, didn't think to. I'm not really sure how to check diodes or the transistor, can you enlighten me?

For diode and transistor testing, see this page:

Electronics Tips: Measurements: Testing Diodes and Transistors

Myself, I find it very straightforward to test using an analog VOM, as per their directions for same.

If you're going to test a transistor, you may find it helpful to download a datasheet so you can identify base vs. collector vs. emitter, and whether it's a PNP or NPN type.

If you desolder diodes or transistors, for testing purposes, try not to heat a pin for more than 5 seconds or so. Also, apply an alligator clip in between the point where you're heating and the device, to serve as a heat sink.