my parts finally arrived today and they are missing some transistors, MTX part numbers refered to the transistor as a to-92, i asked my supplier for a surface mount transistor
MTX replacment number said it is "pnp mpsa92 to-92"
my suppliers part number was "MPSA92" no stock
can i use a TO-92 case if the legs line up correctly?
or
can i sub in mmbta92 SOT
it seems someone is getting the part numbers mixed up. because in the amp they are deffinetly not a TO-92 case. and/or there has been a replacment amd/or substitution. for my 2 options I can get both parts. but ill have to wait a couple weeks again for delivery.
MTX replacment number said it is "pnp mpsa92 to-92"
my suppliers part number was "MPSA92" no stock
can i use a TO-92 case if the legs line up correctly?
or
can i sub in mmbta92 SOT
it seems someone is getting the part numbers mixed up. because in the amp they are deffinetly not a TO-92 case. and/or there has been a replacment amd/or substitution. for my 2 options I can get both parts. but ill have to wait a couple weeks again for delivery.
According to MTX...
loc Q514,515,516,517,518 = PNPMMBTA56SMD
loc Q507,508,509 = PNPMPSATO-92
loc D503 = MMBD4148SE
loc R520,522 = 475 OHM
loc Q519 = NPNMMBTA06SMDSOT
loc Q504,505,506,507,508,509 = NPNPZTA42SMDSOT
you can see that R520 has now failed and it is attached to Q509, i am hoping this is my problem
i have spare MPSA92 here now to try (TO-92 case)
loc Q514,515,516,517,518 = PNPMMBTA56SMD
loc Q507,508,509 = PNPMPSATO-92
loc D503 = MMBD4148SE
loc R520,522 = 475 OHM
loc Q519 = NPNMMBTA06SMDSOT
loc Q504,505,506,507,508,509 = NPNPZTA42SMDSOT
you can see that R520 has now failed and it is attached to Q509, i am hoping this is my problem
i have spare MPSA92 here now to try (TO-92 case)
Attachments
To get the PZTA transistors off of the board, apply a lot of new solder to the tab and the legs. Heat the tab for about 3-5 seconds then lay the iron across all 3 legs to meal the solder on all 3 at once. You have to move from the tab to the legs immediately. Generally, when you do this, you can easily slide/lift the transistor off of its pads.
my supplier is having a hard time locating a "NPN PZT A06 smd sot"
Is there an alternative number to this, I can't even seem to find very much in the way of a data sheet. Usually google has a bunch to offer and when i type in this number I get aprox 2 different options.
The other one seems to be common enough "PNP PZT A56 SMD"
Is there an alternative number to this, I can't even seem to find very much in the way of a data sheet. Usually google has a bunch to offer and when i type in this number I get aprox 2 different options.
The other one seems to be common enough "PNP PZT A56 SMD"
I am starting to think this amp hates me,
I replaced the shorted PZTs and still same symptom of 50v at the speaker outputs, I have replaced atleast 6 different transistors. and everytime I run arund the board looking for shorts and again noting is standing out as shorted.
I even pulled the PSU (75339P) out again looking for a short and nothing. It does get hot when the red protect light is on, but im not blowing that 1k resistor off the board anymore. I dont want to leave the power on till something else explodes because i suspect the power supply will die before anything else.
The only thing I can think to do next is call MTX again and ask for every single part number for that quadrent of the board and just replace everything.
I did find one short but im not sure what it means. It seems to be ground by design (picture enclosed) the pink marks are ground.
Thank you for the soldering technique, it worked very well for something else i was working on.
I replaced the shorted PZTs and still same symptom of 50v at the speaker outputs, I have replaced atleast 6 different transistors. and everytime I run arund the board looking for shorts and again noting is standing out as shorted.
I even pulled the PSU (75339P) out again looking for a short and nothing. It does get hot when the red protect light is on, but im not blowing that 1k resistor off the board anymore. I dont want to leave the power on till something else explodes because i suspect the power supply will die before anything else.
The only thing I can think to do next is call MTX again and ask for every single part number for that quadrent of the board and just replace everything.
I did find one short but im not sure what it means. It seems to be ground by design (picture enclosed) the pink marks are ground.
Thank you for the soldering technique, it worked very well for something else i was working on.
Attachments
Is this a clue to my problem? why do I have such different voltages on the positive PZT?
Also I have illustrated which pieces I have changed.
Another guess would be the NE55 opamp that I pulled earlier in this repair. should I order a new one or would it possibly be at fault and be the cause of this failure? I put it back in place because i was afraid of losing it when i was ordering new parts.
Also I have illustrated which pieces I have changed.
Another guess would be the NE55 opamp that I pulled earlier in this repair. should I order a new one or would it possibly be at fault and be the cause of this failure? I put it back in place because i was afraid of losing it when i was ordering new parts.
Attachments
A couple of findings and a couple of questions.
d400- With the diode removed, my meter on diode test i get .05 both directions and 50 ohms both directions (I am very excited about this)
R409- Out of range and now repaired.
R418+416- these 2 resistors seem to be buddies, with the diode D400 in place I measured very high resistence across to the order of M. so I changed them out suspecting they were out of range although they measured fine out of circuit. All I had to replace them with is 68k. (supposed to be 61.9k), now it measures 33.75k Ohms
Question, Am I close enough with 68k,
R417+R419- These measure up at 31k (61.9/2)
Question, If D400 is bad, It has marked on it 4746AP. I have some options here in my tool box,
1.) I have some that look like the same red glass but are half the size.
2.) I also have one that likes like a replacement and has markings 1N4742A
3.)I also have a multitude of larger ones but they are black not glass like these ones
d400- With the diode removed, my meter on diode test i get .05 both directions and 50 ohms both directions (I am very excited about this)
R409- Out of range and now repaired.
R418+416- these 2 resistors seem to be buddies, with the diode D400 in place I measured very high resistence across to the order of M. so I changed them out suspecting they were out of range although they measured fine out of circuit. All I had to replace them with is 68k. (supposed to be 61.9k), now it measures 33.75k Ohms
Question, Am I close enough with 68k,
R417+R419- These measure up at 31k (61.9/2)
Question, If D400 is bad, It has marked on it 4746AP. I have some options here in my tool box,
1.) I have some that look like the same red glass but are half the size.
2.) I also have one that likes like a replacement and has markings 1N4742A
3.)I also have a multitude of larger ones but they are black not glass like these ones
Last edited:
I was too excited and couldnt wait for a response. So I put the 1N 4742a in place and put power to the amp via the big resistor and instantly locked the new PZTs again, I also blew up the diode too, it is reading the same as the last dead one (.6v in both directions on diode test). I have ordered new ones, this time I ordered 2 of each PZT.
Sorry, I guess i should have waited.
Sorry, I guess i should have waited.
- Status
- This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.