My friend from the local fairground asked if I could look over the amp that ran the sound system. Apparently it just stopped working but that was all he could tell me. Let me start by saying that I am a little out of my league on this, as a component level repairman. I told him I would have a look to see if anything obvious popped out. Anyway, when I opened it up I could smell something burnt, and found that both of the varistors, MOV1 and MOV2 were blown up. I attached a picture. I could replace them but I would guess that something else caused them to fail. Is this a common point of failure or not?
Attachments
Ok. I shorted them out, hooked up my dim bulb tester with a 100 watt bulb and turned it on. Now I get a mechanical sound. Sounds like a relay chattering. Bulb stays brightly lit.
Something is fried.
The schematics are available from Crest (free), but this may not be a good amp for the less experienced to work on.
You should be able to buy a good used Crest CKV amp on eBay for $150 or so, two CKV400 for $100 and $125, a CKS800-2 for $225 (about 3dB less than a CKV, but able to drive a lower impedance). I have bought CKS800V for $100 from time-to-time.
Do they really need 800W?
Add up all the load watttages and add a 30% safety factor.
Check the actual impedance on the line(s).
Hook a 12V AC transformer to each line if you can't borrow an impedance bridge to test the line. Walk around the area and you will be able to hear an improperly connected speaker, it will sound like it's trying to climb out of the ceiling (or off the pole). A 10W ceiling speaker will only draw about 0.3W on 12V, if it was added later without a transformer it will draw 18W!
The schematics are available from Crest (free), but this may not be a good amp for the less experienced to work on.
You should be able to buy a good used Crest CKV amp on eBay for $150 or so, two CKV400 for $100 and $125, a CKS800-2 for $225 (about 3dB less than a CKV, but able to drive a lower impedance). I have bought CKS800V for $100 from time-to-time.
Do they really need 800W?
Add up all the load watttages and add a 30% safety factor.
Check the actual impedance on the line(s).
Hook a 12V AC transformer to each line if you can't borrow an impedance bridge to test the line. Walk around the area and you will be able to hear an improperly connected speaker, it will sound like it's trying to climb out of the ceiling (or off the pole). A 10W ceiling speaker will only draw about 0.3W on 12V, if it was added later without a transformer it will draw 18W!
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