PPX 1600 channel issues |
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scott_fury
Registered User Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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Posted: 10 June 2018 at 11:09pm |
hi,
Was playing out last night and had Channel B go on my Citronic PPX 1600. Luckily it was right at the start and I had a spare 900 in my van, so managed to get away with it. I’ve opened it up and checked fuses, which are all okay. I’ve gone through all resistors with a multimeter and got continuity, although I haven’t checked to see if they are reading the correct values. I have been unable to get a reading for ZD1 diode, but not sure if that would be an issue? There are no signs of any component burn out. I have a very limited understanding of electronics but I am an electrician so not a complete dunce. I’d like to work through it and see if I can diagnose what’s going on, but don’t know where to start. Would anyone be able to give me some tips or advice as to where to look first? Many thanks!
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simonp1100
Young Croc Joined: 01 September 2008 Location: Bristol Status: Offline Points: 1103 |
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Check the following first:
1. Make sure the bridge switch on the back is 100% in stereo mode (these can be a bit temperamental). 2. ZD1 (Looking at the PPX 1200 diagram) is only used to supply a constant voltage of 27V for the mono/bridged LED on the front panel. 3. There are a number of "fusible" resistors on the board (100R X 3 per channel), check these. 4. Check all wirewound resistors (these can go open circuit over time / temperature). 5. Measure the voltage on BOTH 15 volt zener diodes on faulty board (these are used to power the 8 pin op-amp chip). 6. There are also a "switch on muting circuit" which uses a FET (1 per channel), and when i have been repairing these amps in the past i had one which was shorting and audio was just going to ground, check these (think it is a 2N3819). 7. Replace op-amp. 8. Check TRIAC on heatsink that this is not shorting. 9. Check trip on heatsink (100C) is not open circuit. Edited by simonp1100 - 11 June 2018 at 8:31am |
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mini-mad
Old Croc Joined: 13 July 2012 Location: london Status: Offline Points: 6903 |
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..and remember...
Do you know of or have you seen an uncared for and unloved PPX amp? These rare animals are thinning out in the wild and due to irresponsible carelessness of their owner has seen their numbers decline over the years.. Here at the PPX care centre we look after and repair these magnificent beasts and nurse them back to health as part of our care programme within the facility. Our award winning expert GAZ has had a life long dream of one day having racks and racks of these beautiful creatures where they are loved and taking out every weekend for a good hard thrashing... Please donate what you can as it all goes to keeping these rare animals in a happy and loving environment. Call 1-800- GAZ-PPX and start feeling good about yourself today!! |
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If it sounds like a gorilla is trying to escape, turn it down.
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Hemisphere
Old Croc Joined: 21 April 2008 Status: Offline Points: 2272 |
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That's it - forget Save the Children and MSF. Time to put my money where it really matters!
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Dub Specialist Sound
Old Croc Joined: 15 November 2013 Location: Smethwick Status: Offline Points: 4873 |
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Musical Roots Reggae Vibration is Life! for music is sound...sound is vibration...vibration is energy... and energy begets life. Therein lies my passion!...MUSIC IS LIFE...
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jbl_man
Moderator Group Joined: 12 January 2005 Location: London. Status: Offline Points: 11154 |
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Remove the faulty channel B board....unsolder one end of both of the two big
dropper resistors (from memory they are 5k6 3watt on the 1600) ......R48
and r55....see if they are open circuit? As Simon said above, these have a habit of failing over time.
Edited by jbl_man - 11 June 2018 at 11:44am |
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Be seeing you.
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GAZ.
Old Croc Joined: 16 January 2007 Location: Hertfordshire Status: Offline Points: 2433 |
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Doesn't hurt to replace those resistors anyway even If they are not the cause of the problem as they are usually quite burned up. Stand them up off the board when you replace them so they get a bit of air round them, and it stops the board being scorched any further.
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100% Earth Moving Bass
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GAZ.
Old Croc Joined: 16 January 2007 Location: Hertfordshire Status: Offline Points: 2433 |
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So far over 20 fortunate PPX have found a forever home here at the PPX sanctuary. Your continued support is greatfully received. |
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100% Earth Moving Bass
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jbl_man
Moderator Group Joined: 12 January 2005 Location: London. Status: Offline Points: 11154 |
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Here's some we did earlier.... |
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Be seeing you.
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scott_fury
Registered User Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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Hi Simon, Thanks for your reply. That's really helpful. I've gone through a few things tonight but may need a bit more advice. 1 - The bridge switch is recessed and needs a flat head screwdriver to turn. I've adjusted it to make sure but seems fine. 3 - Checked the three fusible resistors. 100.7 - 101.6. 4 - Not sure how to recognise which ones are the wirewound ones? Are they the bigger brown ones? I checked all of these and the only one which didn't read the correct amount is R60 (10R2W) located next to the choke. I could only get 0.2 Ohms across it. 5 - What's the method to measure voltage on a Zener Diode? Do I need to ground the negative somewhere else, or do I measure across the legs of the Diode? I'm not sure I'm doing it right as I keep getting different readings each time. I think you helped me fix an issue with this one before actually. I've brought a couple of PPX's to you a few years ago now. Appreciate you spending time to help out again now! |
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scott_fury
Registered User Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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Hey jbl_man and Gaz. I did see this post when searching through. Mine are okay, but if I get the board out I will replace them. What did you replace them with...? Cheers for the advice.
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scott_fury
Registered User Joined: 28 October 2012 Location: Bristol Status: Offline Points: 319 |
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I've opened my doors to PPX's in need, and have given a home to a
handful of abused machines with various needs and disablities, from
450's with crackly pots to 1200's with only one channel. It's my aim to
provide these worn amplifiers with the same opportunities that other
more younger and lighter products receive.
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