citronic ppx 900 fault

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   come across an old ppx900 in the garage, channel A is working as it should but channel B has the clip light constantly illuminated and is outputting no sound,on inspection on channel B all fuses for the mosfets are fine and the mosfets are running warm on idle which I think is normal behaviour for these amplifiers. where should I look next? anybody had the same issue? thankyou in advance!

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bigtool Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 30 July 2019 Status: Offline Points: 60	Post Options Post Reply Quote bigtool Report Post Thanks(0) Quote Reply Topic: citronic ppx 900 fault Posted: 30 April 2020 at 8:42pm
	come across an old ppx900 in the garage, channel A is working as it should but channel B has the clip light constantly illuminated and is outputting no sound,on inspection on channel B all fuses for the mosfets are fine and the mosfets are running warm on idle which I think is normal behaviour for these amplifiers. where should I look next? anybody had the same issue? thankyou in advance!

simonp1100 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1110	Post Options Post Reply Quote simonp1100 Report Post Thanks(0) Quote Reply Posted: 01 May 2020 at 7:56am
	It may be down to the following:-- 1. Check the mute channel switch on FET's on each channel are not faulty / shorting (TR2 & TR12 2N3819). 2. Check the 100 degree output channel trips are o.k. (should be closed / shorted for normal use). 3. Check each channel driver fuseable resistors (power off on the amplifier and make sure main capacitors have discharged) and each resistor should be 100 ohms. (R37,R42,R43 on channel A & R19,R20,R25 on channel B. This appears to be O.K. as the MOSFET's are running warm on idle, but check anyway. 4. Check that you have near 15V across the following diodes when amplifier is powered up (ZD1,ZD2 on Channel A & ZD3, ZD4 on Channel B). 5. Check the output crowbar Triacs on each channel are not shorting (amplifier powered down), these are mounted on the side of the main output heatsink and are fitted by a small 's' shaped clip, take each one out of circuit and check with a meter. Hope this helps and please be careful due to the high voltage present on the main smoothing capacitors (Make sure these have been discharged BEFORE making any checks or removing of components).

cazmac Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 28 February 2022 Location: London Status: Offline Points: 3	Post Options Post Reply Quote cazmac Report Post Thanks(0) Quote Reply Posted: 28 February 2022 at 8:22pm
	Hi was this ever resolved my amp has the exact same fault. want to get to work on it soon as possible. Thought the OP might be able to narrow the fault finding process down? Regards

cravings Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 30 January 2007 Location: Ireland Status: Offline Points: 7442	Post Options Post Reply Quote cravings Report Post Thanks(1) Quote Reply Posted: 28 February 2022 at 9:19pm
	Simon knows his stuff..

cazmac Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 28 February 2022 Location: London Status: Offline Points: 3	Post Options Post Reply Quote cazmac Report Post Thanks(0) Quote Reply Posted: 02 March 2022 at 8:31pm
	Hi, want to get myself all set up before I start to dismantle, is there any particular brand of components that I should purchase or can anyone recommend a reputable online retailer that sales high quality components? Thanks in advance

simonp1100 Members Profile Send Private Message Find Members Posts Add to Buddy List Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1110	Post Options Post Reply Quote simonp1100 Report Post Thanks(1) Quote Reply Posted: 02 March 2022 at 8:46pm
	Try the following:-- 1. R.S. Components. 2. Farnell In One. 3. Mouser Electronics. 4. Digi-Key. These are all the top 4 component retailers & while you might be able to get components cheaper via Ebay etc alot of stuff maybe fakes from China & there are a lot of fakes around at pesent, so i only use the above for genuine parts. Be warned, due to the pandemic there is a mass component sortage at the moment with very long lead times. Edited by simonp1100 - 02 March 2022 at 8:48pm

cazmac Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 28 February 2022 Location: London Status: Offline Points: 3	Post Options Post Reply Quote cazmac Report Post Thanks(0) Quote Reply Posted: 02 March 2022 at 8:48pm
	Thanks Simon, I had a look at mouser a few days ago, so will probably purchase from them. Thanks for the quick response.

service dept Steve Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 30 January 2010 Location: S.W.London Status: Offline Points: 2034	Post Options Post Reply Quote service dept Steve Report Post Thanks(0) Quote Reply Posted: 03 March 2022 at 5:56pm
	Faults on these amps are rare, after all in period they were buckets of money. The usual fault is that one of the two 15v zener diodes fails short or the resistor feeding it goes open, obviously the give away is that any op amp will have 15v across the power pins where they should have 30v, that would give the described fault and mute the amp
	We are not "They", We are "The others"http://www.servicedept.co.uk -

Madhosting Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 26 January 2023 Location: Wiltshire Status: Offline Points: 2	Post Options Post Reply Quote Madhosting Report Post Thanks(0) Quote Reply Posted: 26 January 2023 at 4:40pm
	Hi. I have a similar fault on one of my PPX 900 amps. Channel A is fine but channel B is very week and distorted. The high frequency sounds do not really come through at all and the base thumps come through as distorted crackles. If I turn the volume right up on the mixer output I get a bit more through but it is incredibly quiet and distorted / crackly. I wonder if any of you knowledgeable people can point me in the right area to have a look at It is one of the older designed amp with the long rocker switch rather then the later designed amps. Thanks

GAZ. Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 16 January 2007 Location: Hertfordshire Status: Offline Points: 2433	Post Options Post Reply Quote GAZ. Report Post Thanks(0) Quote Reply Posted: 26 January 2023 at 6:29pm
	With the amp switched off, switch the bridge mode switch backwards and forwards a few times. The contacts can be a bit dirty and cause the issue you’re having. Happened to one of mine once. I’ve got LOTS of PPX amps
	100% Earth Moving Bass

Madhosting Members Profile Send Private Message Find Members Posts Add to Buddy List New Member Joined: 26 January 2023 Location: Wiltshire Status: Offline Points: 2	Post Options Post Reply Quote Madhosting Report Post Thanks(0) Quote Reply Posted: 26 January 2023 at 8:59pm
	Thanks for the reply, unfortunately I have already checked the bridge switch and input connectors and ruled them out as the culprit. I have noticed one thing that may be a pointer (or maybe not). When you turn the power switch off only the channel A clip light comes on as the capacitors discharge and the PSU voltage drops. Probably a red herring though. Thanks. Richard