CS 800x DDT issue
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CS 800x DDT issue
Hi. I am in the process of repairing a CS 800x amp which was tripping the breaker on poweron. Using a lamp limiter I determined that there was a short, most likely in the power amp section. I pulled and checked all the power transistors and respective resistors. Three of the power trannys were bad in channel A. I replaced them with trannys I ordered from Peavey. The amp tested good with the lamp limiter, so I powered it up and one channel works fine. The other is very quiet and distorted, and as I turn up the gain the DDT lamp flickers and comes on steady at large gain. I tried swapping the preamp board, but the problem persists. I have a reasonably strong electronics background, and build and repair tube amps, but not so familiar with the solid state amps of today. Can anyone guide me on what else I may be missing on the power amp board? BTW, I pulled and tested the triacs on the bad channel as well, and the tested fine.
Re: CS 800x DDT issue
You replaced output transistors, so did you check ALL the associated resistors for opens? That means the power resistors - 0.33 ohm 10w, but also those 1k. Look a little to the left and see three 22 ohm resistors, and don;t leave out the 330 ohm R120 wired base to base on the drivers.
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Re: CS 800x DDT issue
Thanks for the advice Enzo. I will recheck the other resistors...only checked the .33 ohm biggies. A quick question...how does one pull the flat cable from the power board to the preamp board??? That connector is SO tight that I ended up breaking a 1/4w resistor next to one the other day trying to get it apart. Every time I plug them in I dread the possibility of having to unplug them. The hardest connectors I have encountered in 40+ years of electronics work...
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Re: CS 800x DDT issue
Ok, so I realized that the channel that was giving my DDT problems isn't the channel that I replaced the power transistors in. That channel works just fine. It is the other channel that isn't working correctly. I have pulled all the resistors in the power section and they all check out fine. I pulled the two driver transistors on that channel as well and they are fine. I pulled the triac on that channel and it is fine. Soooo, since I tried swapping the preamp boards to no avail, what is left? This amp has given me fits...
Re: CS 800x DDT issue
A small screwdriver pushed under the edge of the connector near one end, then twisted to wedge the thing up a millimeter, then do the other end. Once it is started, you have room for more tool use.
One of my absolute FAVORITE tools is the OTC O-ring seal pick, I bought at an auto parts store decades ago. it is similar to the pointy thing dentists use to scrape your teeth.
https://www.amazon.com/OTC-7312-Ring-Se ... B000P70QPW
I use that a lot to get under sticky connector housings.
You may have swapped driver cards, but how about the little input circuits? Is the signal reaching that driver card clean?
One of my absolute FAVORITE tools is the OTC O-ring seal pick, I bought at an auto parts store decades ago. it is similar to the pointy thing dentists use to scrape your teeth.
https://www.amazon.com/OTC-7312-Ring-Se ... B000P70QPW
I use that a lot to get under sticky connector housings.
You may have swapped driver cards, but how about the little input circuits? Is the signal reaching that driver card clean?
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Re: CS 800x DDT issue
Many thanks Enzo. After careful examination, and resoldering some suspect connections on the second channel
power amp section, all is well once again. So now I hope I have a flood of these coming in for repair, as I have
them pretty well figured out! BTW, love your pic!
power amp section, all is well once again. So now I hope I have a flood of these coming in for repair, as I have
them pretty well figured out! BTW, love your pic!
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Re: CS 800x DDT issue
Rascalrick, do you repair Peavy equipment? I have an issue and you sound knowledgeable.
Re: CS 800x DDT issue
Hi Rob. Just start a new thread for your amp, and ask about your issue. We will either be able to help or not.