Hey guys, my nephew has a Marshall guitar amp (5203 aka Master Reverb 30) and looks like IC1 needs replaced as per a few guitar amp forums.
From reading, sounds like the small IC's on these amps go out often and need replaced, so I plan to solder in 8-pin sockets just for making things easier in the future.
I opened it up and the IC's are
3 x MC1458CP1 IL8635 Motorolla
1 x Portugal TL071CP 419BB Texas Instruments
Figured replace all at once and add sockets, or at least order them all in case it's not IC1 and one of the others. Problem is I believe they're obsolete, so I can either pay $35CAD and buy off eBay from the USA and get them in a week or two, or dirt cheap, like 10 for $2, but China so 6-8 weeks.
Is there a direct replacement for these? I see LM1458's listed often, but honestly, I have basic soldering skills and that's about it. If I know what I need I can fix it, but I don't know what the numbers and letters mean to know what will/won't work. Hoping to order from Tayda or DigiKey.ca so maybe next weekend I can get this fixed for him.
Thanks
From reading, sounds like the small IC's on these amps go out often and need replaced, so I plan to solder in 8-pin sockets just for making things easier in the future.
I opened it up and the IC's are
3 x MC1458CP1 IL8635 Motorolla
1 x Portugal TL071CP 419BB Texas Instruments
Figured replace all at once and add sockets, or at least order them all in case it's not IC1 and one of the others. Problem is I believe they're obsolete, so I can either pay $35CAD and buy off eBay from the USA and get them in a week or two, or dirt cheap, like 10 for $2, but China so 6-8 weeks.
Is there a direct replacement for these? I see LM1458's listed often, but honestly, I have basic soldering skills and that's about it. If I know what I need I can fix it, but I don't know what the numbers and letters mean to know what will/won't work. Hoping to order from Tayda or DigiKey.ca so maybe next weekend I can get this fixed for him.
Thanks
An MC1458 is a dual op amp and a TL071 is a single op amp.
Neither are obsolete but a TL072 is slightly less noisy than the 1458.
TL072CP Operational Amplifiers - Op Amps | Mouser United Kingdom
TL071ID Operational Amplifiers - Op Amps | Mouser United Kingdom
They rarely fail, measure the voltages around them. Pin 1 should be around zero volts as should pin 7.
Neither are obsolete but a TL072 is slightly less noisy than the 1458.
TL072CP Operational Amplifiers - Op Amps | Mouser United Kingdom
TL071ID Operational Amplifiers - Op Amps | Mouser United Kingdom
They rarely fail, measure the voltages around them. Pin 1 should be around zero volts as should pin 7.
When I go to Mouser.ca or DigiKey.ca the MC1458CP1 shows obsolete and not available... though DgiKey.ca has a listing for it still with 0 stock but min. order of 760.
They do list a bunch similar, like the MC1458P... but I don't know the difference between CP1 or P.
The TL071 is probably fine, no one mentioned having to swap that one in the forums, but wanted it on-hand just to be safe, but IC1 which is the MC1458CP1 chip, some people said they've had to replace that 2-3 times over the years which is why I want to install a socket. Easier to replace in the future, and less chance of damage to the IC when soldering.
Is the MC1458P the equivalent of the current MC1458CP1?
They do list a bunch similar, like the MC1458P... but I don't know the difference between CP1 or P.
The TL071 is probably fine, no one mentioned having to swap that one in the forums, but wanted it on-hand just to be safe, but IC1 which is the MC1458CP1 chip, some people said they've had to replace that 2-3 times over the years which is why I want to install a socket. Easier to replace in the future, and less chance of damage to the IC when soldering.
Is the MC1458P the equivalent of the current MC1458CP1?
1) this is your amp schematic:
Excellent little amp, loud enough for small Club work, plus rehearsals, etc.
2) do NOT repeat NOT replace parts at random "just because you read something similar in a Forum" , even less Guitar Forums which are not staffed by Techs, that putting it mildly.
And even IF that worked for that Forum poster, who says you have the exact same Technical problem? You did NO troubleshooting whatsoever.
3) now to the main point: what is the actual problem you are trying to solve?
Then we may be able to help with *your* amplifier, which is not the others.
For comparison: would you order prescription glasses using Aunt Emma´s Optician recipe?
Or treat blood own pressure problems with a friend´s suggested Medicines?
Same thing
Excellent little amp, loud enough for small Club work, plus rehearsals, etc.
2) do NOT repeat NOT replace parts at random "just because you read something similar in a Forum" , even less Guitar Forums which are not staffed by Techs, that putting it mildly.
And even IF that worked for that Forum poster, who says you have the exact same Technical problem? You did NO troubleshooting whatsoever.
3) now to the main point: what is the actual problem you are trying to solve?
Then we may be able to help with *your* amplifier, which is not the others.
For comparison: would you order prescription glasses using Aunt Emma´s Optician recipe?
Or treat blood own pressure problems with a friend´s suggested Medicines?
Same thing
If IC1 has failed, (TL072), replace it and fit clamping diodes, anode from pin7 to pin 3 and the second diode cathode to pin 4 and anode to pin 3. That will stop the IC from failing again. Use 1N4148/1N914 or similar.
As I say, check the voltages. Pins 1, 2, 3, 5, 6 and 7 should all be around zero volts. If they are the IC is probably fine.
As I say, check the voltages. Pins 1, 2, 3, 5, 6 and 7 should all be around zero volts. If they are the IC is probably fine.
"You did NO troubleshooting whatsoever"
... bit of an assumption there. Input jack and pots were a possible cause, cleaned and tested fine. Zener diodes also listed as a possible cause, and both tested fine as well. Next (and only other) listed cause is the IC1 which seems to be the fix when all else fails. No other real fixes listed so figured swap it out. Few people on the forum for Marshall amps said they've had to swap IC1 out 2-3 times in the past 20-30yrs since the amp is from the '80s. This one is 1988, which is 2yrs newer than that schematic, and maybe why the numbers don't match (CA1458 vs MC1458SP1). That or looks possible someone has been inside it before so maybe the IC's were swapped already. In any case... SOME troubleshooting was done.
Basically... pre-amp volume, below lvl3 is fine no issues. Once I turn the dial up to 4 or more, when you get distortion for playing rock and such, when I hit a chord the sound comes out of the speaker for a brief moment and instantly fades and cuts out. There are 2 LED lights on the board LED1 and LED2. LED2 is lit, and gets brighter the louder I turn the amp on... LED1 is off. When I strike a chord on the guitar, the LED1 flickers on and fades to off, same as the sound.
Chatted on a couple of forums, a Marshall Amp forum, a general guitar and gear forum, then found this older post on a solid state amp forum that was almost identical except master volume not preamp. But someone popped up with the same issue as me with preamp volume and said it was his IC1 chip.
Marshall 5203
So... jack is fine, pots are fine, zener diodes are fine... figured next thing to tackle were the IC's.
Again, only seems to be an issue, when preamp is turned up beyond lvl3, when you hit 4 and up the amp just fades to silent very quickly.
... bit of an assumption there. Input jack and pots were a possible cause, cleaned and tested fine. Zener diodes also listed as a possible cause, and both tested fine as well. Next (and only other) listed cause is the IC1 which seems to be the fix when all else fails. No other real fixes listed so figured swap it out. Few people on the forum for Marshall amps said they've had to swap IC1 out 2-3 times in the past 20-30yrs since the amp is from the '80s. This one is 1988, which is 2yrs newer than that schematic, and maybe why the numbers don't match (CA1458 vs MC1458SP1). That or looks possible someone has been inside it before so maybe the IC's were swapped already. In any case... SOME troubleshooting was done.
Basically... pre-amp volume, below lvl3 is fine no issues. Once I turn the dial up to 4 or more, when you get distortion for playing rock and such, when I hit a chord the sound comes out of the speaker for a brief moment and instantly fades and cuts out. There are 2 LED lights on the board LED1 and LED2. LED2 is lit, and gets brighter the louder I turn the amp on... LED1 is off. When I strike a chord on the guitar, the LED1 flickers on and fades to off, same as the sound.
Chatted on a couple of forums, a Marshall Amp forum, a general guitar and gear forum, then found this older post on a solid state amp forum that was almost identical except master volume not preamp. But someone popped up with the same issue as me with preamp volume and said it was his IC1 chip.
Marshall 5203
So... jack is fine, pots are fine, zener diodes are fine... figured next thing to tackle were the IC's.
Again, only seems to be an issue, when preamp is turned up beyond lvl3, when you hit 4 and up the amp just fades to silent very quickly.
IC1 isn't the TL072... That's IC3
IC1,2 and 4 are the MC1458CP1's... though diagram shows a slightly different part number, the chips inside say MC1458CP1.
Unfortunately the rest is gibberish to me.
Again... basic soldering skills, that's it. Most I know is soldering pots and caps to guitars, and repaired a few LCD screens replacing blown cheap caps. So IC wise... will any 8-pin IC with 1458 in the name work? like LM1458N? See Tayda has those in stock.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.