Chevin Research A-series schematic

[HaaiFaai]

Chevin uses an old Hafler patent for the power amp( called grounded emittor/source transnova?), also a Motorola or IRF patent for the power supply (electronic balast, no ic's just self oscillating with a diac and small signal transformer for driver) so nothing special here. The mosfets will produce some (most of the..10-20 dB?)gain and can be bolted without isolation as both upper and down banks are "earthed" if I am correct (it's way too long ago since I've serviced them...)
The speaker connects between earth of psu and earth of bolted together power mosfets..a bit odd when seen at first..but very smart..;-) they do get good reviews.

Testing is indeed difficult, perhaps some lightbulbs..the ones they use for rebuilding/re-decorating homes..?

the best test is half power...that will show if there's enough thermal cooling or not..full power will not generate as much heat as half or quarter of power.
Hopes this helps

[Netlist]

Thank you very much.
I managed to fix the amp without schematic, last time I talked to the customer it was still playing. I'll keep your advice when another one comes in.

/Hugo

[DaDe]

Can someone help me with my problem?

I have two a1000 Chevin amp on wich the fans are dead. I traced the problem down to two burned resistors (100 Ohm) In the middle of the cooling bank. I tried replacing them but found that the IRF740 mosfet was dead to.
With my rather basic expierince in amp design after looking at the datasheet I decided I could easely bridge the Mosfet by connecting pin 3 to the massa, and therefore leaving the fans on constantly.
Works like a charm on one amp, but the other keeps blowing the resistors. Has anyone expirience with this kind of problem, and a solution?
Also a schematic of the design would be higly appreciated.

[Netlist]

Try replacing the two 100µF caps in the fan control circuit.
I will mail you the diagram of that fan control, don't ask for the complete schematic, I don't have it.

/Hugo

[DaDe]

Thanks for the diagram,

I will try to replace the caps this weekend (I don't have much time during the week), but I have strong feelings these won't make much of a difference since the resistors just smoke away, Even 4 500 Ohm 1/2 Watt resisters in parrallel (= 110 ohm 1 Watt) are blown away really fast. I am more thinking in direction that one of the two Supply's is faulty, therefore generating to much current trough the resistors.

On both amps I'm also going to replace the hardware tot the ground instead of the mosfet by a 10 or 100 ohm resistor 5 Watt. I'm geussing these should temper the current flowing trough both 100 ohm resistors.

Is there anyone who sees a mistake in my thoughts?

DaDe

[Netlist]

You will notice that there is not a lot to test in that circuit.
A few zeners and some diodes apart from the mosfet.
It would surprise me that the PSU is the culprit. If that part goes out of control, you might expect an awful lot of smoke.

/Hugo

[Dr Herringbone Dread]

Good afternoon,

I bought a used chevin q6 with one of the volume knobs broken off. I recently opened the amps and put in a replacement pot. When I reassembled and powered up the amp, the red clip light for the channel remains lit and the output is shockingly low and bad. I took out the new pot and stuck back in the old one, but the problem remains.

I checked the capacitors with a multimeter and they all work fine, and nothing appears damaged.

Does anyone recognise these symptoms? Have I inadvertently damaged something?

[bear]

Boy do I feel dopey - I didn't realize it was an SMPS type amp... geez. Only 6 years later the thread pops up and I see it... ha ha.

Talk about slow and dense, eh? :b

_-_-bear

[MrLayout]

Hi, I am new to this forum. I am an electronic engineer by profession but more on the digital side - not too good with analogue stuff!

I am trying to repair a Chevin Research A1000 power amp for a friend and was wondering if anyone has any schematics for this or similar amp.

Fault description: Channel A seems to work fine and the fans are Ok too. The output from channel B is noticeably distorted but seems to be about the correct volume, I think. Nothing inside looks obviously burnt, or anything.

Any help would be gratefully received!

Thanks.