Hi folks I have a Perreaux 8000c ..lately the left channel started to get crackly and staticky and also little pop sounds .I have to mention that I have 3 6000c aswell that have very similar symptoms .All seem to be on the left channel, I have tried swapping the cables around and it's definitely not from the source its from the amps.Is this a common problem with these amps . What is it about the left side does anybody know.i have tried to find schematics and a repair manual for them but can't seem to find anything on the net.
Anyway back to the 8000c ...I got this one off a friend as He was throwing it out ,he told me that only one channel works.when I took it home and plugged it in the power and hooked everything up both channels worked fine for a few weeks then the left stopped working.I pulled the covers off and had a look around and it was immediately obvious that it had been fiddled with .On the right channel it has a combination of original hitachi transistors and the BUZ901 and BUZ906 transistor replacements ,but it all works great on that side. On the left channel all the transistors are original ,I'm not exactly sure how to check if the are in working condition (if anybody knows how to test these please be kind enough to explain this to me).Also on the left channel one of the 4.7ohm large ceramic resistor was burnt out showing zero resistance on my multimeter.One of the 10uf caps was bulged on the top which is probably stuffed.Anyway I changed all the 10uf caps with Panasonic ones on both channels and I also changed the 4.7ohm Ceramic resistor . Upon further investigation I noticed that one of the left channel fuse housing was damaged causing the fuse to not make contact at the ends so no current is going through ..I replaced the fuse housing aswell..after changing these components I though it might work but still no sound on the left channel ...so if anybody has ideas that can help please do I would greatly appreciate it.
Anyway back to the 8000c ...I got this one off a friend as He was throwing it out ,he told me that only one channel works.when I took it home and plugged it in the power and hooked everything up both channels worked fine for a few weeks then the left stopped working.I pulled the covers off and had a look around and it was immediately obvious that it had been fiddled with .On the right channel it has a combination of original hitachi transistors and the BUZ901 and BUZ906 transistor replacements ,but it all works great on that side. On the left channel all the transistors are original ,I'm not exactly sure how to check if the are in working condition (if anybody knows how to test these please be kind enough to explain this to me).Also on the left channel one of the 4.7ohm large ceramic resistor was burnt out showing zero resistance on my multimeter.One of the 10uf caps was bulged on the top which is probably stuffed.Anyway I changed all the 10uf caps with Panasonic ones on both channels and I also changed the 4.7ohm Ceramic resistor . Upon further investigation I noticed that one of the left channel fuse housing was damaged causing the fuse to not make contact at the ends so no current is going through ..I replaced the fuse housing aswell..after changing these components I though it might work but still no sound on the left channel ...so if anybody has ideas that can help please do I would greatly appreciate it.
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Those are 'lateral FET' transistors and generally very rugged. As long as they do not read short circuit between Drain and Source then there is a good chance they are fine.
'Zero ohms' is actually a short circuit. Did you mean 'infinity' or open circuit when describing the resistor ?
As with anything like this, a circuit diagram is essential to help you work on it. An experienced tech could figure most things out by visually looking at it in detail, but to advise in detail on the forum is going to need a circuit diagram.
'Zero ohms' is actually a short circuit. Did you mean 'infinity' or open circuit when describing the resistor ?
As with anything like this, a circuit diagram is essential to help you work on it. An experienced tech could figure most things out by visually looking at it in detail, but to advise in detail on the forum is going to need a circuit diagram.
Hi Mooly... Thanks for your reply ...sorry I meant open circuit ..no continuity.
I have been trying to locate a schematic but have had no luck so far...meantime I'll check out the fest...I am a newby with electronics so please be patient with me
I have been trying to locate a schematic but have had no luck so far...meantime I'll check out the fest...I am a newby with electronics so please be patient with me
here for 8000B version:
PERREAUX 8000B SCH Service Manual download, schematics, eeprom, repair info for electronics experts
likely to be similar enough
FIRST: DISCHARGE POWER SUPPLY
make sure the pots are clean (of course)
check for cold/cracked solder joints especially where you see heat damage or discoloration on pcb's.
Since this unit is stereo and one channel is working I recommend checking and comparing all semiconductor junctions passively (power off) using the diode function on your meter. If you can't find an anomaly (especially a short on an output Q; i.e. where you found the bad cap and R) then power up, let it warm up, and hit the fet diff. amps with a little freeze spray (lightly) to see if this causes increased noise or popping. The problem you describe is typically there.
If not, or you're not sure what I'm talking about you should really get a very experienced tech. to work on this problem as advanced troubleshooting techniques may be required. Other than the freeze spray trick you should NOT work on this unit while powered on (being a self described NEWBIE). If you're not sure what you're doing, don't do it! Find someone experienced to help you.
PERREAUX 8000B SCH Service Manual download, schematics, eeprom, repair info for electronics experts
likely to be similar enough
FIRST: DISCHARGE POWER SUPPLY
make sure the pots are clean (of course)
check for cold/cracked solder joints especially where you see heat damage or discoloration on pcb's.
Since this unit is stereo and one channel is working I recommend checking and comparing all semiconductor junctions passively (power off) using the diode function on your meter. If you can't find an anomaly (especially a short on an output Q; i.e. where you found the bad cap and R) then power up, let it warm up, and hit the fet diff. amps with a little freeze spray (lightly) to see if this causes increased noise or popping. The problem you describe is typically there.
If not, or you're not sure what I'm talking about you should really get a very experienced tech. to work on this problem as advanced troubleshooting techniques may be required. Other than the freeze spray trick you should NOT work on this unit while powered on (being a self described NEWBIE). If you're not sure what you're doing, don't do it! Find someone experienced to help you.
Just tested the fest on the left channel with my digital multimeter in continuity mode and the 5 hitachi k176 all measured at 076 on the dmm and the the 5 Hitachi J56 on the same channel measured at 290 ..does this mean the fets are ok
A/B the readings between channels. Do they match up? If so the problem is most likely not there. Check all values of all components between channels to see if they match. A painstaking approach but good experience. An ESR meter can be useful to identify bad caps. (build one from a kit, it's cheap) You can build a diode curve tracer/tester to interface with your scope: Is the simplest diode curve tracer a perfect circuit?
a very useful tool for A/B testing of P/N junctions in circuit.
a very useful tool for A/B testing of P/N junctions in circuit.
There are long thin parallel tracks carrying +/- supply voltages.....dust, fog juice etc causes leakage currents to signal tracks.
Cleanse PCB's (Isopropyl + brush), blanket resolder, cleanse PCB's, confirm operation (use bulb tester, one channel at a time), cal bias currents/offsets, spray PCB's with conformal coating, enjoy.
Dan.
Cleanse PCB's (Isopropyl + brush), blanket resolder, cleanse PCB's, confirm operation (use bulb tester, one channel at a time), cal bias currents/offsets, spray PCB's with conformal coating, enjoy.
Dan.
Can you identify the 4.7 ohm that was open circuit ? Was it the one in the Zobel network ? which is R28 in the circuit mlfcva linked to. If so, then the problem is/was high frequency instability.
Another approach to working on this would be to measure voltages with the amp on. I would always advise using a DBT (dim bulb tester) to prevent damage. You would probably have to turn the bias down on both channels to get meaningful results with a DBT. Turning the presets to minimum resistance (so Q4 and Q5 collectors become linked) would give zero bias. The amp should otherwise perform normally.
Its very like the old Hitachi application note circuit (and the Maplin lateral FET amp).
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