substance on board, corrosion - Page 4

jol50 · 14th December 2007, 02:16 AM

I ran a sub and speakers with it, it seemed to work fine. These seem to crank up pretty good compared to some other cheap amps though I never have priced them. One could run a mild system off this one little amp, it could get a 12 going pretty good. I could not tell quality without it being in a car, but they have some power. Each side bridged is 200w they say.

jol50 · 17th December 2007, 02:44 AM

Since this is the same issue maybe, thought I would just add on here. I have an alpine 3542 2x60 that works, just was taking a look and....it has close to 170mv offset on one channel and -160 on the other? Is that not huge? The board is a mess (organizationally) and I don't have time to tear it down right now to find differential amplifiers but assuming there is a problem here. It has this voltage right at the outputs and no heat. I checked my ancient 3518 and it had 1 and 2mv.

Perry Babin · 17th December 2007, 03:30 AM

The 3542 uses driver ICs (upc1270h) instead of discrete differential amplifiers.

There is a bypass capacitor in the feedback circuit. If it's leaking (electrically), it could cause the offset. If the cap isn't leaking, the IC could be defective. The datasheet says they're supposed to produce no more than ~50mv of offset.

jol50 · 17th December 2007, 04:20 AM

Pretty sure I want to use this in my car until/if I can bridge the 3518s. 50mv? It is 169 right and -158 left. I'll see if I can look at it closer tomorrow.

jol50 · 18th December 2007, 02:52 PM

It does have the NEC uPC1270H's. I'll try to get it apart tonight.

jol50 · 19th December 2007, 07:46 PM

I worked on it a little, I tested the two caps next to each IC and they appear to act the same, run up/down the same but I don't know the proper way to determine leakage. Looking for the data on the IC now.

jol50 · 21st December 2007, 06:04 PM

I think I found the right caps, in the bias circuit? They both show the same ohms in circuit of 1.4x K ohms. Maybe I will just order new all of it as I'm not getting anywhere this way. I can pull the caps and test first, I'll do that.

jol50 · 31st December 2007, 01:31 AM

I really need to get this last problem child back together. Ticks me off because this was supposed to be a good amp I bought to use and can't.

So I went looking at these upc1270h. My reasoning says it is hard to believe both of them are out or both channels have a bad cap/etc though sure it is possible. Tried to find something that could affect both channels but no luck. So I checked every cap around them and just ohms read mounted they seem to look ok and each channel very similar.

Took some readings on the upc1270h, amp powered up idle nothing else hooked to it. Pin 4 is input and 5 is inverted, they read for pin 4 185mv and 176, for pin 5 195 and 186. So I have about 10mv going into it?

Pin 7 & 8 for bias are running a C3423 on the heat sink with plenty of mv and near the same readings I didn't record. Output of the upc1270h's for upper is 400mv and lower -700mv within 20mv of each other.

Offset at speaker leads read -172mv and -162 for left ch, with 13.1v B+ on amp. Vccd/p is +/-29.5v. I don't yet know what the muting pin 3 and phase comp pin 6 are for.

Should they have that much input mv or offset on it at idle? The heatsink is off and transistors on rails, they get a little warm.

17th December 2007, 03:30 AM	#33
Perry Babin diyAudio Member Join Date: Nov 2003 Location: Louisiana	The 3542 uses driver ICs (upc1270h) instead of discrete differential amplifiers. There is a bypass capacitor in the feedback circuit. If it's leaking (electrically), it could cause the offset. If the cap isn't leaking, the IC could be defective. The datasheet says they're supposed to produce no more than ~50mv of offset. __________________ Links >> Basic Car Audio Amp Repair --- Basic Car Audio Electronics --- Basic Transistor Testing --- Basic Switching Power Supply Design --- Basic Computer Skills << Links

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14th December 2007, 02:16 AM	#31
jol50 diyAudio Member Join Date: Nov 2007	I ran a sub and speakers with it, it seemed to work fine. These seem to crank up pretty good compared to some other cheap amps though I never have priced them. One could run a mild system off this one little amp, it could get a 12 going pretty good. I could not tell quality without it being in a car, but they have some power. Each side bridged is 200w they say.

17th December 2007, 02:44 AM	#32
jol50 diyAudio Member Join Date: Nov 2007	Since this is the same issue maybe, thought I would just add on here. I have an alpine 3542 2x60 that works, just was taking a look and....it has close to 170mv offset on one channel and -160 on the other? Is that not huge? The board is a mess (organizationally) and I don't have time to tear it down right now to find differential amplifiers but assuming there is a problem here. It has this voltage right at the outputs and no heat. I checked my ancient 3518 and it had 1 and 2mv.

17th December 2007, 04:20 AM	#34
jol50 diyAudio Member Join Date: Nov 2007	Pretty sure I want to use this in my car until/if I can bridge the 3518s. 50mv? It is 169 right and -158 left. I'll see if I can look at it closer tomorrow.

18th December 2007, 02:52 PM	#35
jol50 diyAudio Member Join Date: Nov 2007	It does have the NEC uPC1270H's. I'll try to get it apart tonight.

19th December 2007, 07:46 PM	#36
jol50 diyAudio Member Join Date: Nov 2007	I worked on it a little, I tested the two caps next to each IC and they appear to act the same, run up/down the same but I don't know the proper way to determine leakage. Looking for the data on the IC now.

21st December 2007, 06:04 PM	#37
jol50 diyAudio Member Join Date: Nov 2007	I think I found the right caps, in the bias circuit? They both show the same ohms in circuit of 1.4x K ohms. Maybe I will just order new all of it as I'm not getting anywhere this way. I can pull the caps and test first, I'll do that.

31st December 2007, 01:31 AM	#38
jol50 diyAudio Member Join Date: Nov 2007	I really need to get this last problem child back together. Ticks me off because this was supposed to be a good amp I bought to use and can't. So I went looking at these upc1270h. My reasoning says it is hard to believe both of them are out or both channels have a bad cap/etc though sure it is possible. Tried to find something that could affect both channels but no luck. So I checked every cap around them and just ohms read mounted they seem to look ok and each channel very similar. Took some readings on the upc1270h, amp powered up idle nothing else hooked to it. Pin 4 is input and 5 is inverted, they read for pin 4 185mv and 176, for pin 5 195 and 186. So I have about 10mv going into it? Pin 7 & 8 for bias are running a C3423 on the heat sink with plenty of mv and near the same readings I didn't record. Output of the upc1270h's for upper is 400mv and lower -700mv within 20mv of each other. Offset at speaker leads read -172mv and -162 for left ch, with 13.1v B+ on amp. Vccd/p is +/-29.5v. I don't yet know what the muting pin 3 and phase comp pin 6 are for. Should they have that much input mv or offset on it at idle? The heatsink is off and transistors on rails, they get a little warm.

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