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The amp is done. We sent it out with the mute circuit dis-connected.
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vintagekiki replied
Question.
1. If FM212R has no signal at inputs, and an empty jack plug is installed in J4, what is DC voltage on TP29....
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TP29 reads 5mv with an empty plug in the input jack. With nothing plugged in it reads about 3 volts.
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vintagekiki replied
Today, 02:31 AM
Originally posted by booj
TP23 is supposed to be -31 VDC and its -30.3V...
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vintagekiki replied
08-26-2021, 11:03 PM
FM-65R schematic are very similar, only here you have some voltage test points....
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vintagekiki
- Check mute line contacts on jacks J1, J2, J4.
They're there
FM212R power off. At jacks J1, J2, J4 nothing is connected....
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Ok I'll try to make this simple. Apparently, I have made some progress. When I dis-abled the mute circuit (quadrant A5), by cutting R73, The DC on...
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Ok, so I just left the speaker wires dis-connected, which allowed me to leave the amp on for troubleshooting. Everything looked normal up to the output of...
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g1 They were
Jon Snell Popping noises. Thx for the insight.
J M Fahey Thanks for being nice
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Yes, of course, a light bulb limiter. Have one. If it keeps R84 from getting hot I can leave the amp on long enough to troubleshoot.
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Forgot to mention the reference designators for Q16 and Q17 are incorrect. They are not 2N4001 and 2N4003, but 2N4401 and 2N4403.
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Fender Frontman 212R DC on output
Getting almost the full negative supply voltage at the output. Amp started out with making loud popping sounds. Fixed that by changing the 2SD1857 (Q14) and...
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Chuck H. Under load meant driving a signal to the point of clipping. No load meant no signal. I was talking about the load to the power supply. I was expecting...
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Hiwatt DR501 low output
DR501 that puts out about 20 watts. I've checked voltages, swapped output transformer, output tubes, preamp tubes, replaced a suspiciously browned output...
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Found it! Two bad solder connections. One from the gain control in the distortion circuit and one to the chip holder that holds the switching IC. Kind of...
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Just replace the 6.8k with a 10k pot. He can control the mids the way he wants then....
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V1 voltages: Pin 6 - 95.5v, pin 8 - .535v. V3 voltages: Pin 1 - 195v, Pin 3 - 1.58v. I believe the master works in clean mode but I'll check again.
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V2 voltages are 1, 254v - 3, 2.48v - 6, 206v - 8, 1.33v
I lifted C11 and C12 and the distorted signal seemed to get a bit louder, but still way below...
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JCM 800 2205 Low boost channel output
With nothing plugged into the footswitch jack the amp is in boost mode. The amp has very little volume and the Gain and Master controls have very little effect...
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The schematic shows one side of the filament voltage going to ground. this will cause some 60HZ hum. Placement of the output transformer can make a difference,...
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The problem was dirty tube sockets. I replaced them all. Of course now one channel is out, but the hum issue is resolved.
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