XS2300 Blk Repair

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Oppenheimer
Posts: 5
Joined: Sat Dec 19, 2020 6:07 pm

XS2300 Blk Repair

Post by Oppenheimer »

Hello, I am starting a repair on an xs2300 blk that has several problems, as well as previous repairs that were questionable at best.


Does any one have any wiring diagrams for this model?
lilviper
Posts: 270
Joined: Tue Nov 06, 2012 9:30 pm

Re: XS2300 Blk Repair

Post by lilviper »

Oppenheimer wrote:Hello, I am starting a repair on an xs2300 blk that has several problems, as well as previous repairs that were questionable at best.


Does any one have any wiring diagrams for this model?
they aren't going to give you them, even if they had one.

best to do is post pics and ask targeted questions.

Sent from my SM-G988U using Tapatalk
Oppenheimer
Posts: 5
Joined: Sat Dec 19, 2020 6:07 pm

Re: XS2300 Blk Repair

Post by Oppenheimer »

lilviper wrote:
Oppenheimer wrote:Hello, I am starting a repair on an xs2300 blk that has several problems, as well as previous repairs that were questionable at best.


Does any one have any wiring diagrams for this model?
they aren't going to give you them, even if they had one.

best to do is post pics and ask targeted questions.

Sent from my SM-G988U using Tapatalk
lilviper, Thanks for the response. Yea, through my research I kind of figured that, but I thought it wouldn't hurt to ask. I've got the parts coming to rebuild the whole channel as was suggested by 1moreamp in a post several years ago. As I get into it, I will ask more specific questions.

I am getting into amp repair as a hobby/challenge. I was looking for one that had problems to practice on and this one happened to fall into my lap. I guess it would have been better to find one that had info readily available.
lilviper
Posts: 270
Joined: Tue Nov 06, 2012 9:30 pm

Re: XS2300 Blk Repair

Post by lilviper »

Oppenheimer wrote:
lilviper wrote:
Oppenheimer wrote:Hello, I am starting a repair on an xs2300 blk that has several problems, as well as previous repairs that were questionable at best.


Does any one have any wiring diagrams for this model?
they aren't going to give you them, even if they had one.

best to do is post pics and ask targeted questions.

Sent from my SM-G988U using Tapatalk
lilviper, Thanks for the response. Yea, through my research I kind of figured that, but I thought it wouldn't hurt to ask. I've got the parts coming to rebuild the whole channel as was suggested by 1moreamp in a post several years ago. As I get into it, I will ask more specific questions.

I am getting into amp repair as a hobby/challenge. I was looking for one that had problems to practice on and this one happened to fall into my lap. I guess it would have been better to find one that had info readily available.
It usually is easiest to fix those things not held as state secrets, or you could take the time to generate a schematic, then analyze the circuts.. From what i have been able to glean theres very little differences between then amp series. pg kinda had a basic design they stuck with. you could also check with the Facebook page?

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Oppenheimer
Posts: 5
Joined: Sat Dec 19, 2020 6:07 pm

Re: XS2300 Blk Repair

Post by Oppenheimer »

So I changed both output FETS on the bad channel, found a few resistors that were toast or out of spec and changed them. Found three capacitors that were out of spec and or bulging changed them.

The amp will now play on both channels and things seem to be relatively even on both channel speaker outputs.
DC offset seems good 7mV and 5.5 mV

It is now drawing less than 1 amp at idle, whereas before it was drawing ~10 amps at idle.

Input at 12Vdc:
Rail/Secondary +28.1 Vdc and -27.4 Vdc

I think this is voltage for the differential pairs and bias circuit, on the cathode of SF-24 rectifier diode is 35.3 Vdc

On the bad channel I can not get the bias set any lower than 8.9 mV (pot full C.C.) it was more than 100 mV before I changed the components as listed above, whereas the good channel was set at 1.3 mV. I have removed one leg of all diodes from the pcb on the bad channel and the seemed okay.

The lower bipolar supply is high at 18 Vdc on both channels. I think it should be +/- 15 Vdc. The Vs max of the 4560D's is +/- 18 Vdc. Also the drivers, the 200 ohm 1W parallel resistors and one capacitor, which is one of the caps that were changed, get very hot at idle in this area (Q102,Q103,Q106,Q107,C34 and the two 1W resistors) on both channels. The Voltage drop across the resistors is 10.2 Vdc each, 28Vdc to ~ 18Vdc going to the pre-amp board. The readings on the 1N44744A 15V Zener is 18 Vdc on the cathode and 0.000 on the anode.
Also, when I apply heat to the transistors in this section the bias voltage goes from 8.9 mV to 1.8 mV. When heat is removed bias voltage goes back to ~ 8 mV.

So I think my two main problems right now are the bias circuit/bias current and the voltage of the lower supply being to high.

Does anyone have any suggestions of where to go next?

Thank you.
Attachments
XS2300 lower supply.jpg
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Jacampb2
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Location: Beaverton 48612

Re: XS2300 Blk Repair

Post by Jacampb2 »

Your rails all sound to be correct. The ±15v rails are zener regulated and will be a little "loose" at idle. Once there is a bit of load while driving the preamp, I suspect they will drop down closer to where they belong. You could try replacing the pair of zeners, they possibly are leaky, but I really doubt it.

In these amps it doesn't pay to leave any of the transistors in a channel which was blown. The mpsa56 transistors are pennies, replace them. Most of the diodes are 1n4148 and a few zeners, it's best to replace them. Sometimes parts behave differently during DC testing them they do in operation. It costs like 3 bucks to rebuild a channel, I wouldn't normally recommend throwing parts at something, but in these amps it's really the best course of action.

That said, did you by any chance use irf540N or irf540Z mosfets?
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
Oppenheimer
Posts: 5
Joined: Sat Dec 19, 2020 6:07 pm

Re: XS2300 Blk Repair

Post by Oppenheimer »

Jacampb2,

I used the Vishay IRF540PBF. I swapped the FETs from one channel to the other and the bias issue followed the new FETs.

Yea, the +/- 15 V rails came down to ~ +/- 16.3 Vdc when the pre-amp board was connected.

I have changed all of the mpsa56s and mpsa06s as well as the differential pair of 2sc2362s, (they came from B+D Ent. so I don't know if they are original parts), in that channel and the channel is now working, but I still could not get the idle bias voltage to come down. So with the guidance of Perry, I replaced the 1.27 K resister connected to the pot with a 5.1K resistor, which did lower the idle bias voltage to 1.1 mV, but it is not adjustable with the pot. I did run the amp into a dummy load until thermal shutdown while monitoring the idle current and it stayed stable at 1.8 mV then came back to 1.1mV when the amp cooled down. I would still like it to be adjustable.

I have all of the parts to change all of the diodes in that channel, so I will do that and report back.

Can you tell me what component is circled in the image. It is glass cased, has no markings on it, does not appear to have a polarity (pads on board both circular)? Each channel has one each.

Thank you for your reply and help.
Attachments
xs2300 4 - Copy_LI (2) resized.jpg
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Jacampb2
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Re: XS2300 Blk Repair

Post by Jacampb2 »

Most times devices in the do-41 package that are not diodes are RTDs. Pg did not often use them in their designs, but in the xs and tantrum amps they used a 10k NTC RTD as part of the bias control circuitry. I cannot tell from the picture if these are RTDs, but their circuit designation will be "R" if they are the thermistors. They do not often go bad unless moisture has migrated into the body. You should be able to see corrosion under magnification of there is damage. They also should read approximately the same resistance at ambient temperature.

That said, if one is bad, I don't know of the exact replacement part number for you. Thermistors come in all sorts of different "curves" and temperature ranges. It's possible to determine the necessary info from measurements of a part in good condition.

If as you say, the bias issue followed the new mosfets, then it sounds like it's related you your replacement parts. Did you buy them from an authorized distributor? If you have any extra, it might be necessary to crack one open and look at the die. I've got pictures of the die of an original type 540 and one of one of the "next gen" suffixed parts to give you an idea of comparison. I'll see if I can find it and upload it on a moment. It's really pretty obvious the differences, even too the naked eye.
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
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Jacampb2
Mad Scientist
Posts: 1562
Joined: Sat Apr 19, 2008 11:57 pm
Location: Beaverton 48612

Re: XS2300 Blk Repair

Post by Jacampb2 »

Pain in the ass, but I found it. The one on the *left* is the only style that can be used in a linear amplifier unless it was specifically designed to run the new next gen parts.
Attachments
FB_IMG_1584709018195-picsay.jpg
FB_IMG_1584709018195-picsay.jpg (26.5 KiB) Viewed 3254 times
Last edited by Jacampb2 on Thu Feb 11, 2021 7:49 pm, edited 2 times in total.
M: M100, M44 for a custom amp project
Zx: Zx500, Zx450, Black Zx350
ZxTi: 4 Zx600Ti's, 1 Zx400Ti
Ti: 5 800.1's & 900.7 for a custom amp project. 1 1200.1, 1 1000.2
Tantrum: 2 1200.1's, 1 600.4, 1 500.2
XS: XS6600
Oppenheimer
Posts: 5
Joined: Sat Dec 19, 2020 6:07 pm

Re: XS2300 Blk Repair

Post by Oppenheimer »

I bought them from Mouser. I bought 10, so I will crack one open tomorrow and see what I can see.

Thanks for finding and posting the pic.
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