Hey guys,
Can you share your thoughts with me on the following.
My Mc2200 sometimes, when I switch it on, the left channel remains muse. If I switch it off and on again everything is ok and both channel are working. Another thing, some times it looks like the same channel shows less power.
Any ideas what am I facing here?
Just for your info the amp has never been repaired so all the capacitors are original. Could this be the issue or the relay?
Regards
Can you share your thoughts with me on the following.
My Mc2200 sometimes, when I switch it on, the left channel remains muse. If I switch it off and on again everything is ok and both channel are working. Another thing, some times it looks like the same channel shows less power.
Any ideas what am I facing here?
Just for your info the amp has never been repaired so all the capacitors are original. Could this be the issue or the relay?
Regards
That does sound like the protection relay. If there is an adequate replacement that can be made to fit easily, simply replace it, otherwise you'd have to open the old one and check whether it is still salvageable. In case anything more abrasive than some blotting paper soaked in contact cleaner is required, it's pretty much toast and complete failure only a matter of time.
Probably the speaker relay, but also check the input sensitivity slide switch on the back, they get dirty.
On the 05 models with the meters, the ribbon cable in the front panel gets carbon tracks on its ends and the meters read funny.
Can be a great sounding amplifier, even close to 40 years old.
I have a mod list for the caps if you want to go through things, make it sound tighter in the bass, more detailed in the high-end.
(for MC502, 2120/2125/2200/2205)
On the 05 models with the meters, the ribbon cable in the front panel gets carbon tracks on its ends and the meters read funny.
Can be a great sounding amplifier, even close to 40 years old.
I have a mod list for the caps if you want to go through things, make it sound tighter in the bass, more detailed in the high-end.
(for MC502, 2120/2125/2200/2205)
This is what I do:
"Which caps are they DJK? I'll try them in my 2125."
Add one 47µF across each ±42V rail at the main filter caps
Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)
Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)
Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)
Add a 0.1µF film in parallel with C219, 220 (feedback cap)
Add a 0.1µF film in parallel with Q215, 216 (bias transistor)
Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)
Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)
I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.
I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.
I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.
Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.
The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.
Even though this changes no measurable performance specification, it will change the sound more than you can believe.
Jackhammer bass from an amp with a DF of only 14?
************************************************************
You should just be able to jump across the input caps and sensitivity switch with no problems there.
If you're trying to use better input jacks the grounding and the 0.01µF caps to ground become important. If you try and eliminate the input attenuator you will probably need a cap to ground from the node of R201 and C203 on the driver card, somewhere between 10pF~100pF.
Good luck.
"Which caps are they DJK? I'll try them in my 2125."
Add one 47µF across each ±42V rail at the main filter caps
Add a 0.01µF~0.1µF film cap in parallel with C239, 240 (little board on the input jacks, very tight for space)
Add a 0.1µF film in parallel with C203, 204 (input coupling cap to impedance buffer)
Add a 0.1µF film in parallel with C207, 208 (output coupling cap from impedance buffer)
Add a 0.1µF film in parallel with C219, 220 (feedback cap)
Add a 0.1µF film in parallel with Q215, 216 (bias transistor)
Add a 0.1µF film in parallel with C305, 306 (±15V regulator outputs)
Add a 0.1µF film in parallel with D304, 305 (reference diodes for regulators)
I cut off all the push on connectors in the power supply and speaker relay and soldered them direct. I soldered a pair of 0.1µF film across the speaker relay contacts and cleaned the relay contacts with a sheet of paper and applied De-oxit.
I sprayed De-oxit on the RCA jacks, cleaned the input sensitivity selector switch (very important), and the edge connectors for the L and R amp boards.
I removed the 10-32 screws on the main filter caps and used De-oxit before replacing.
Do not move the chassis with the bottom off, the glass could crack. Put it on a small piece of carpet to help turn at different angles.
The 47µF are under a lot of stress, I used 100V caps even though they only run at 42V.
Even though this changes no measurable performance specification, it will change the sound more than you can believe.
Jackhammer bass from an amp with a DF of only 14?
************************************************************
You should just be able to jump across the input caps and sensitivity switch with no problems there.
If you're trying to use better input jacks the grounding and the 0.01µF caps to ground become important. If you try and eliminate the input attenuator you will probably need a cap to ground from the node of R201 and C203 on the driver card, somewhere between 10pF~100pF.
Good luck.
At this point one has to stop replacing the "usual suspects", and actually diagnose what is wrong with the amp. At what stage does the sound stop? Connector in? Pot wiper? Some oxidized input selector switch? connector to input board? input DC block capacitor? bad solder joint on board? the very rare bad resistor or transistor weld inside the case? Very rare blown semiconductor? connector out of the input board to the main board? parts around the VAS? Driver stage? connector to output transistors? output transistors or emitter resistors? output relay? connectors to the output terminal?
This diagnosis can be done with a 1. sound probe 2. Analog VOM with DC blocking capacitor & 2 VAc and 20 vAc scale ( or something close) 3 Oscilloscope. You exercise the amp with either a signal generator, or much cheaper, a pocket FM radio tuned to a rock station with an earphone to input connector adaptor Y cable.
DVM in my experience produce random numbers on the AC scale on music. They also average signals over 2 to 4 seconds, so you can miss things that come & go. analog VOM can respond up to under 1 hz. Scopes are good but a chock full of electrolytic capacitors that cause problems of their own in the 10 to 20 year timeframe. My analog VOM, I bought it in 1986, no maintenanc required. A sound probe is an audio amp with variable gain with an input protector to protect the input transistors from huge DC voltages or spikes from change of DC voltage. the probe is two .047 uf caps 200 v rated, series each with a 1000 ohm resistor. Then the output of the two resistors is connected to two LED, 1.6 v on voltage, line to line, to clamp the two wires to 1.6 v max. Then the two wires go to the hot and ground of a regular amp/speaker combo. Computer speakers used to be perfect for this, but they were all built so cheaply they all need repair by now, themselves.
A schematic and parts layout of the amp is very helpful, but not absolutely required if you have any experience. After you find the place where the sound stops, then you check DC voltages around there with the DVM, look for visual clues, use cold spray or a hair dryer, various ways to get the circuit to act up while you are looking carefully at it. Do circuit traces have the same DC voltage on both end component leads? Do EB or diode junctions have about .6 v or else a big back voltage? Do collectors of analog amp transistors between 1/3 & 2/3 of the supply voltage? do the two inputs and outs of an op amp all have about the same Dc voltage? Do capacitors have different DC voltages on the two ends? Is the voltage drop across a resistor within that predicted by the current limit established by what wattage a resistor it is?
Note, with power on, use only one hand at a time. Voltage over 24 from one hand to the other can stop your heart. Use alligator clip leads and keep your off hand in your pocket. Furthermore voltage over 1 at high current can burn your finger to charcoal through a ring or other jewelry. No jewelry on hands or neck. A light bulb box in series with the AC line can save parts if your probe slips, and prevent explosions if an output transistor decides to short out. Pay attention and don't work distracted by cell phone children or TV.
Have fun with conquering this problem. It can be a great learning experience, without the tuition, expensive books, and commute expense of a community college course. If you want to know more, the books with obsolete problem sets from those electronics courses are very worth buying and studying. I found Thomas Floyd, Electronic Devices, the Electron Flow version, ed 2, very useful, $2 at the charity resale shop.
This diagnosis can be done with a 1. sound probe 2. Analog VOM with DC blocking capacitor & 2 VAc and 20 vAc scale ( or something close) 3 Oscilloscope. You exercise the amp with either a signal generator, or much cheaper, a pocket FM radio tuned to a rock station with an earphone to input connector adaptor Y cable.
DVM in my experience produce random numbers on the AC scale on music. They also average signals over 2 to 4 seconds, so you can miss things that come & go. analog VOM can respond up to under 1 hz. Scopes are good but a chock full of electrolytic capacitors that cause problems of their own in the 10 to 20 year timeframe. My analog VOM, I bought it in 1986, no maintenanc required. A sound probe is an audio amp with variable gain with an input protector to protect the input transistors from huge DC voltages or spikes from change of DC voltage. the probe is two .047 uf caps 200 v rated, series each with a 1000 ohm resistor. Then the output of the two resistors is connected to two LED, 1.6 v on voltage, line to line, to clamp the two wires to 1.6 v max. Then the two wires go to the hot and ground of a regular amp/speaker combo. Computer speakers used to be perfect for this, but they were all built so cheaply they all need repair by now, themselves.
A schematic and parts layout of the amp is very helpful, but not absolutely required if you have any experience. After you find the place where the sound stops, then you check DC voltages around there with the DVM, look for visual clues, use cold spray or a hair dryer, various ways to get the circuit to act up while you are looking carefully at it. Do circuit traces have the same DC voltage on both end component leads? Do EB or diode junctions have about .6 v or else a big back voltage? Do collectors of analog amp transistors between 1/3 & 2/3 of the supply voltage? do the two inputs and outs of an op amp all have about the same Dc voltage? Do capacitors have different DC voltages on the two ends? Is the voltage drop across a resistor within that predicted by the current limit established by what wattage a resistor it is?
Note, with power on, use only one hand at a time. Voltage over 24 from one hand to the other can stop your heart. Use alligator clip leads and keep your off hand in your pocket. Furthermore voltage over 1 at high current can burn your finger to charcoal through a ring or other jewelry. No jewelry on hands or neck. A light bulb box in series with the AC line can save parts if your probe slips, and prevent explosions if an output transistor decides to short out. Pay attention and don't work distracted by cell phone children or TV.
Have fun with conquering this problem. It can be a great learning experience, without the tuition, expensive books, and commute expense of a community college course. If you want to know more, the books with obsolete problem sets from those electronics courses are very worth buying and studying. I found Thomas Floyd, Electronic Devices, the Electron Flow version, ed 2, very useful, $2 at the charity resale shop.
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you get a signal generator or a $5 transistor radio. For the radio ou buy a earphone to dual RCA plug converter cable. For the signal generator you buy a Y cable of suitable type. You exercise both channel inputs with the same signal.
then you go through all the points mentioned in post 11, looking for the first stage where the signal levels are different. A DVM won't help much, except the $200 RMS versions, because the inexpensive ones produce random number on music. I don't like the $200 RMS DVM because they will ignore ultrasonic oscillation. An analog VOM with blocking cap, or a scope, will show ultrasonic oscillation. The earliest stage where the signals are different, there is your problem.
Personally when I replace e-caps, I sound check after every pair or so to make sure I didn't make an error. When the sound gets worse instead of better, your mistake is right where you just worked. If you did them all at once, you have to do this point by point debug routine to find your error. Or part failure you caused.
then you go through all the points mentioned in post 11, looking for the first stage where the signal levels are different. A DVM won't help much, except the $200 RMS versions, because the inexpensive ones produce random number on music. I don't like the $200 RMS DVM because they will ignore ultrasonic oscillation. An analog VOM with blocking cap, or a scope, will show ultrasonic oscillation. The earliest stage where the signals are different, there is your problem.
Personally when I replace e-caps, I sound check after every pair or so to make sure I didn't make an error. When the sound gets worse instead of better, your mistake is right where you just worked. If you did them all at once, you have to do this point by point debug routine to find your error. Or part failure you caused.
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1. DVM for DC & Ohms. I use Sears non-autoranging since the autorangers always start at the wrong voltage. Harbor freight can work but not always
2. Analog VOM with 2 VAC & 20 VAC scales + .047 uf blocking cap plus clip leads OR scope with 10x probe with +-- 80 v capability. (lots of the cheapy import scopes are only +-40 or 50 capable). 3. battery powered transistor radio with earphone jack. I like this better than $40 signal generator from mcm because rock stations have a beat you can see in the pointer of the VOM or scope, which proves you looking at music, and not oscillation. I also like cheap radio instead of cell phone because if amp puts DC out the input jack you've blown a $5 radio, not a $600 cell phone.
4. trash speakers for test in case of DC out event; I use car radio speakers from Salvation Army resale shop. And or 8 ohm 225 watt load for full power tests (voltage out on 8 ohm resistor) to check your rail caps, if you're going to in the future test amps with expired life rail caps.
All the used scopes I bought expired from e-cap and vacuum tube problems. My Simpson 266-XLPM VOM is 30 years old and has no e-caps. Cheaper VOM like the GC ones sold at hardware store can work if have 25 VAC scale. You can modify 50 VAC scale with one resistor change if you're on very limited budget.
2. Analog VOM with 2 VAC & 20 VAC scales + .047 uf blocking cap plus clip leads OR scope with 10x probe with +-- 80 v capability. (lots of the cheapy import scopes are only +-40 or 50 capable). 3. battery powered transistor radio with earphone jack. I like this better than $40 signal generator from mcm because rock stations have a beat you can see in the pointer of the VOM or scope, which proves you looking at music, and not oscillation. I also like cheap radio instead of cell phone because if amp puts DC out the input jack you've blown a $5 radio, not a $600 cell phone.
4. trash speakers for test in case of DC out event; I use car radio speakers from Salvation Army resale shop. And or 8 ohm 225 watt load for full power tests (voltage out on 8 ohm resistor) to check your rail caps, if you're going to in the future test amps with expired life rail caps.
All the used scopes I bought expired from e-cap and vacuum tube problems. My Simpson 266-XLPM VOM is 30 years old and has no e-caps. Cheaper VOM like the GC ones sold at hardware store can work if have 25 VAC scale. You can modify 50 VAC scale with one resistor change if you're on very limited budget.
I just purchased a MC2200 from an original owner. It was shipped from Wisconsin to Connecticut. The unit had been sent back to McIntosh by the original owner for bulb replacement twice over the years, but it still checked in spec, so further work was not performed (amazing). The amp and wooden case look as new, but when connected to my C45 there was no output. The headphone jack works in unison with the respective channel volume controls, just no speaker output. ???
Looking at the schematic, I thought the speaker relay may be involved. My understaning of electronics is rudimentary (built a bunch of Heathkit products and Ham radio operator in my youth and more recently some Audio Note kits), but will glady accept advice on what I can do at home, before sending out to McIntosh.
doctorgpz
Looking at the schematic, I thought the speaker relay may be involved. My understaning of electronics is rudimentary (built a bunch of Heathkit products and Ham radio operator in my youth and more recently some Audio Note kits), but will glady accept advice on what I can do at home, before sending out to McIntosh.
doctorgpz