Chris, I'll measure the base of Q25 in the morning. I didn't realise I hadn't measured it since taking the bulb out. I only had 19v there before.
I looked for the DMOD diode and it looks like it's not on the board.
Bugger, I thought this would help trace back to see the location of DMOD but I've not got enough of the board in.
Also the bit that has me confused is you can see R67 is connected to the collector of Q24, in the drawing it goes through R68 before going to Q24.
You can also see there are some mods on the board, there is a capacitor soldered across a resistor. I can't see that in the drawing either.
Amptech, Yes we lifted the legs on R63 and R64 to float the protection circuit. I also got 5v on where the level led board connects to the output. I have the this board removed at the moment while we sort the protection circuit.
R68 does look to be correct but I'll take it out to check it.
I looked for the DMOD diode and it looks like it's not on the board.
Bugger, I thought this would help trace back to see the location of DMOD but I've not got enough of the board in.
Also the bit that has me confused is you can see R67 is connected to the collector of Q24, in the drawing it goes through R68 before going to Q24.
You can also see there are some mods on the board, there is a capacitor soldered across a resistor. I can't see that in the drawing either.
Amptech, Yes we lifted the legs on R63 and R64 to float the protection circuit. I also got 5v on where the level led board connects to the output. I have the this board removed at the moment while we sort the protection circuit.
R68 does look to be correct but I'll take it out to check it.
Got around to taking another look at this today.
I swapped out:
C5, 16, 24, 25, 29, 54, 56, 60,
Z3, 4
Q20, 21, 23, 24, 25, 45 (basically the transistors in the protection circuit)
I've found that swapping out Z3 and Z4 didn't make much difference, Z3 seems better but Z4 seems to be dragging down. It starts at -6.2v then starts heading down.
The other side of R57 stays at -92.3V so it's not the supply.
I thought one of the two transistors Q9 and Q10 might be to blame so swapped them out and it's made to difference.
What could be causing the voltage at Z4 to drift??
I swapped out:
C5, 16, 24, 25, 29, 54, 56, 60,
Z3, 4
Q20, 21, 23, 24, 25, 45 (basically the transistors in the protection circuit)
I've found that swapping out Z3 and Z4 didn't make much difference, Z3 seems better but Z4 seems to be dragging down. It starts at -6.2v then starts heading down.
The other side of R57 stays at -92.3V so it's not the supply.
I thought one of the two transistors Q9 and Q10 might be to blame so swapped them out and it's made to difference.
What could be causing the voltage at Z4 to drift??
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I'm happy to report this amplifier is now coming out of protect mode.
Chris was right about the issue being in the protect circuit and in the area of Q24 and Q25.
In the end I had to get my head around how the protect circuit worked and kept reading the explanation on the back page of the pdf file I found.
In the end it was trial and error in measuring and removing parts. I started to suspect Z7 as I couldn't the 9.1v and then I found 24v on the other side of R69.
I then removed R69 to find it open circuit. Luckily I found a spare 24k resistor that I could use, stuck it in, turn it on and the the beautiful sound of the relays clicked in.
Next I was worried about the Level display board as I hadn't had that back on the board as I found it to be putting 7v on to the speaker terminals. I felt like I took a risk putting it back in without any other work but it all seemed fine after installing it back in.
I'm now getting 0.1mv on the one channel and -0.3mv on the other.
I think next I'd like to make sure everything is all ok to put the amplifier back in to service and to make any modifications required to make the amplifier more reliable.
Thank you to ChrisTech and Amptech for your help.
Chris was right about the issue being in the protect circuit and in the area of Q24 and Q25.
In the end I had to get my head around how the protect circuit worked and kept reading the explanation on the back page of the pdf file I found.
In the end it was trial and error in measuring and removing parts. I started to suspect Z7 as I couldn't the 9.1v and then I found 24v on the other side of R69.
I then removed R69 to find it open circuit. Luckily I found a spare 24k resistor that I could use, stuck it in, turn it on and the the beautiful sound of the relays clicked in.
Next I was worried about the Level display board as I hadn't had that back on the board as I found it to be putting 7v on to the speaker terminals. I felt like I took a risk putting it back in without any other work but it all seemed fine after installing it back in.
I'm now getting 0.1mv on the one channel and -0.3mv on the other.
I think next I'd like to make sure everything is all ok to put the amplifier back in to service and to make any modifications required to make the amplifier more reliable.
Thank you to ChrisTech and Amptech for your help.
On a lot of threads I've read about the poor cooling through the case. I was thinking of getting some passive type heat sinks for the FET's but the ones I like are so expensive.
I like these
But they are around £10!
I'll probably get these.
There are two pots per channel, ones the DC offset and the other says "set Iq"
It also says on the drawings
I guessed this is the Iq pot and set it accordingly and the DC offset I've set to as close to zero as possible, is that correct?
I changed the Opamp IC the other week but I think the original one was slightly better so I'll be putting that back in.
I like these
An externally hosted image should be here but it was not working when we last tested it.
But they are around £10!
I'll probably get these.
An externally hosted image should be here but it was not working when we last tested it.
There are two pots per channel, ones the DC offset and the other says "set Iq"
It also says on the drawings
I guessed this is the Iq pot and set it accordingly and the DC offset I've set to as close to zero as possible, is that correct?
I changed the Opamp IC the other week but I think the original one was slightly better so I'll be putting that back in.
Unfortunately, I have no access to dummy loads. I'll take a look on eBay as I really need to get some at some point.
I'll look in to soak tests. I have access to a thermal camera at work so that could come in handy to see any weak components.
When I was adjusting the pots I found them to be very jumpy, would it be worth me replacing them or I might try washing them through with contact cleaner first?
I'll look in to soak tests. I have access to a thermal camera at work so that could come in handy to see any weak components.
When I was adjusting the pots I found them to be very jumpy, would it be worth me replacing them or I might try washing them through with contact cleaner first?
Hi all sorry to hijack this post but I have a ra4001 on the bench now its in protect mode I have about 2v of dc offset on one channel
its from one of the local nightclub's that we maintain I have put one of our QSCs in its place wile we try and sort it
I have done cold checks on the protect circuit and found r61 o/c and also replaced caps around there also checked components around q5/6/7 etc in the signal stage but still not found the culprit yet !!
the amp works if I connect our “Chinese” Pro sound test speaker before the relays even with our 100w test lamp in series with the mains so I assume the output stage is ok on this one
these amps sound fantastic as I have another one ive had over 10 years now and its never missed a beat and still going strong and is on rental in another venue running mid-tops on a Shermman rig, they are easy to work on but however the PCB print is another thing
busy weekend coming up so ill get back to it this next week and when I sort it ill post back as may help others on here .. I know its a old amp but shame to scrap it as its in very good condition
its from one of the local nightclub's that we maintain I have put one of our QSCs in its place wile we try and sort it
I have done cold checks on the protect circuit and found r61 o/c and also replaced caps around there also checked components around q5/6/7 etc in the signal stage but still not found the culprit yet !!
the amp works if I connect our “Chinese” Pro sound test speaker before the relays even with our 100w test lamp in series with the mains so I assume the output stage is ok on this one
these amps sound fantastic as I have another one ive had over 10 years now and its never missed a beat and still going strong and is on rental in another venue running mid-tops on a Shermman rig, they are easy to work on but however the PCB print is another thing
busy weekend coming up so ill get back to it this next week and when I sort it ill post back as may help others on here .. I know its a old amp but shame to scrap it as its in very good condition
i'm happy this morning to find this subject !!
i have a lot of C-AUDIO amp and 2 are defective .
I never looked at the problem because I bought them for parts (k1058 / j162) but I have three that work and it works really well.
I will take the time to read the whole subject, thanks for the research
i have a lot of C-AUDIO amp and 2 are defective .
I never looked at the problem because I bought them for parts (k1058 / j162) but I have three that work and it works really well.
I will take the time to read the whole subject, thanks for the research
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