I hope someone with more knowledge than I can help me out on this.
I bought this as not working on one channel. Various problems have been noted, with a couple of fried opamps and switches, parts for which are on order.
I have a vague theoretical knowledge, but am a bit stumped by some components which test as diodes but as they're terribly small SMD they haven't enough markings to allow me to replace them. The same with some possible BJTs, marked 'ABL' and 'CBG'.
I've drawn out the circuit from just beyond the input, to the opamp where both channels meet, as far as I can make out. I wonder if someone can look at it and tell me if it looks like a real circuit, or if I've misinterpreted some component type. This is for one of the two channels, with the 10k pot being the gain control.
As I'm getting different DC readings for both channels, I am trying to work out where the current is flowing when it shouldn't but can't replace components if I don't know what they are! If this circuit looks legit (perhaps a differential amplifier, though I'm guessing here) at least I can try dropping in some BJTs and checking the DC levels.
I bought this as not working on one channel. Various problems have been noted, with a couple of fried opamps and switches, parts for which are on order.
I have a vague theoretical knowledge, but am a bit stumped by some components which test as diodes but as they're terribly small SMD they haven't enough markings to allow me to replace them. The same with some possible BJTs, marked 'ABL' and 'CBG'.
I've drawn out the circuit from just beyond the input, to the opamp where both channels meet, as far as I can make out. I wonder if someone can look at it and tell me if it looks like a real circuit, or if I've misinterpreted some component type. This is for one of the two channels, with the 10k pot being the gain control.
As I'm getting different DC readings for both channels, I am trying to work out where the current is flowing when it shouldn't but can't replace components if I don't know what they are! If this circuit looks legit (perhaps a differential amplifier, though I'm guessing here) at least I can try dropping in some BJTs and checking the DC levels.
You might try searching some SMD marking code databases and similar resources, a couple of examples:
Marking of electronic components, SMD Codes AB, AB**, AB***, AB-**, AB-***, AB4T, AB=***, ABD, ABD***, ABE***, ABG, ABH, ABK*, ABL*, ABM*, ABN*, ABP*, ABT***, ABU***, ABW, ABX, ABX*, ABY*, Ab. Datasheets BCW60B, BD48E24G, BD48K24G, BL3406B-1.2V, DTA114TL-AE3, DTA114TL-AL3, DTA114TL-AN3, MAX14578AEEWC, MAX14578EEWC , MAX1510ETB, MAX6314US49D1-T, MAX8902AATA+, MAX8902BATA+, MIC803-26D3VC3, MIC803-26D3VM3, MMBD4448HTS, MMBTA43, MMBZ5226B, RP130Q131A, RT8009-25GJ5, RT8009-25PJ5, RT9011-GSGJ6, RT9011-GSPJ6, RT9193-15PU5, RT9818A-31PU3, RT9818E-40PY, SA57000-25D, SA57000-25UK, SA57000-28D, SA57000-28UK, SA57000-29D, SA57000-29UK, SA57000-30D, SA57000-30UK, SA57000-31D, SA57000-31UK, SA57000-33D, SA57000-33UK, SA57000-36D, SA57000-36UK, SY6288ACAC, SY6288BCAC, SY6288CCAC, SY6288DCAC, SY8008BAAC.
ABL marking code, ABL smd code marking, MAX6411BS46-T to MAX6309UK31D1 - Hotenda Marking Code Searching
For SMD diodes in a mic preamp, most are likely small signal diodes similar to 1n4448, or else maybe zeners. Voltage readings from a working channel may be helpful clues.
Marking of electronic components, SMD Codes AB, AB**, AB***, AB-**, AB-***, AB4T, AB=***, ABD, ABD***, ABE***, ABG, ABH, ABK*, ABL*, ABM*, ABN*, ABP*, ABT***, ABU***, ABW, ABX, ABX*, ABY*, Ab. Datasheets BCW60B, BD48E24G, BD48K24G, BL3406B-1.2V, DTA114TL-AE3, DTA114TL-AL3, DTA114TL-AN3, MAX14578AEEWC, MAX14578EEWC , MAX1510ETB, MAX6314US49D1-T, MAX8902AATA+, MAX8902BATA+, MIC803-26D3VC3, MIC803-26D3VM3, MMBD4448HTS, MMBTA43, MMBZ5226B, RP130Q131A, RT8009-25GJ5, RT8009-25PJ5, RT9011-GSGJ6, RT9011-GSPJ6, RT9193-15PU5, RT9818A-31PU3, RT9818E-40PY, SA57000-25D, SA57000-25UK, SA57000-28D, SA57000-28UK, SA57000-29D, SA57000-29UK, SA57000-30D, SA57000-30UK, SA57000-31D, SA57000-31UK, SA57000-33D, SA57000-33UK, SA57000-36D, SA57000-36UK, SY6288ACAC, SY6288BCAC, SY6288CCAC, SY6288DCAC, SY8008BAAC.
ABL marking code, ABL smd code marking, MAX6411BS46-T to MAX6309UK31D1 - Hotenda Marking Code Searching
For SMD diodes in a mic preamp, most are likely small signal diodes similar to 1n4448, or else maybe zeners. Voltage readings from a working channel may be helpful clues.
Thank you Markw4! I stupidly forgot to mention what I HAD come up with searching the databases. The two that sounded reasonable were the Toshiba 2SA1312, and its counterpart 2SC3324. They are marketed for audio use in pre-amplifiers, and the others in the lists I was looking at (there are very few I found with only three letters) were either the wrong package type or were (to me) esoteric ICs that I couldn't see having an application in the signal path of a microphone pre-amplifier!
The new component tester also considers them PNP and NPN transistors.
To try testing, I've tacked on some 1n4448 diodes and BC327 and BC548 through-hole parts as I have no SMD. There is still current being drawn somewhere, and the two channel voltages do not match, but having disconnected the logic switch IC which had an internal short, there isn't -5V all over the channel 2 example of the circuit above any more.
I will test one of the removed diodes and try to discover whether it is a zener or not. It certainly behaves like a diode and has a line at one end, which my component tester considers the cathode.
The new component tester also considers them PNP and NPN transistors.
To try testing, I've tacked on some 1n4448 diodes and BC327 and BC548 through-hole parts as I have no SMD. There is still current being drawn somewhere, and the two channel voltages do not match, but having disconnected the logic switch IC which had an internal short, there isn't -5V all over the channel 2 example of the circuit above any more.
I will test one of the removed diodes and try to discover whether it is a zener or not. It certainly behaves like a diode and has a line at one end, which my component tester considers the cathode.
After testing up to 20V I decided they were just small signal diodes, and I've just received some after I messed up (I ordered some SOD523 rather than SOD323).
I bought some of the Toshibas mentioned above, and they arrived with the same three letter codes on - a good guess!
With those in place on both channels and a replacement 74HC4053D, I have output on both channels through headphones, and through the USB to be monitored in Audacity. I think that's a cautious success, though I'll see after I get it back in its case...
I bought some of the Toshibas mentioned above, and they arrived with the same three letter codes on - a good guess!
With those in place on both channels and a replacement 74HC4053D, I have output on both channels through headphones, and through the USB to be monitored in Audacity. I think that's a cautious success, though I'll see after I get it back in its case...