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Thread: Peavey XR 696F - I made a booboo

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    Quote Originally Posted by g1 View Post
    This is very strange. Resistors almost never short. Is it's body marked as a 100K resistor?
    It was an SMD marked 104, I double checked with a magnifying glass in case my eyes were lying to me!

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    Lifetime Member Enzo's Avatar
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    R110/116 are not there as a voltage divider per se, they are bleeder/balance resistors for the stacked filter caps, C110/115. The resistors make sure the voltage is equally shared between the two caps.

    At Q103 you show the 86v rail turning into 48v at the collector, and then at the base it is both 48 and 86v. Obviously this is in error. The collector should have the full 86v as they are wired together. 48v on the base seems right, as it is set by the two 24v zeners in series. 34v output is very low.

    In my 65 years of soldering, I do not recall a shorted resistor. I guess it makes more sense in an SM part.

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    Quote Originally Posted by Enzo View Post
    R110/116 are not there as a voltage divider per se, they are bleeder/balance resistors for the stacked filter caps, C110/115. The resistors make sure the voltage is equally shared between the two caps.

    At Q103 you show the 86v rail turning into 48v at the collector, and then at the base it is both 48 and 86v. Obviously this is in error. The collector should have the full 86v as they are wired together. 48v on the base seems right, as it is set by the two 24v zeners in series. 34v output is very low.

    In my 65 years of soldering, I do not recall a shorted resistor. I guess it makes more sense in an SM part.
    Once I've had a decent nights sleep I'll go over all the measurements again. I'll take Q103 out so I can get a good look at the tracks running under it to see where they go as its possible I've crossed paths trying to follow them, maybe I should take measurements with Q103 removed. Looking over my notes I don't seem to have "ticked" Q103 as replaced, seven others have a tick but not that one, so best I take it and be sure!

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    Click image for larger version. 

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    OK I popped out the Q103, it tests fine, so i think I did replace it, but I have two spare so I can always pop in a fresh one. Measurements on the pads, left to right are;

    0.2v / 86.4v / 48.4v

    EDIT:

    Is the silk screen for the transistor orientation wrong?! E should be on the first pin on the left, but the silk screen would have B on the first pin on the left, which is wrong.

    I swapped the transistor around and it's now passing 47v

    Now to carry on trouble shooting the rest of it!

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    Last edited by jondoe; 11-17-2019 at 04:12 PM.

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    I've never seen that silk screen symbol, but I also would have read that as 1,2,3 left to right, but since R111 is connected between base and collector (1 and 2) then it has to be 3,2,1 Maybe the dashed lines are supposed to represent a heatsink on that transistor?

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    Quote Originally Posted by glebert View Post
    I've never seen that silk screen symbol, but I also would have read that as 1,2,3 left to right, but since R111 is connected between base and collector (1 and 2) then it has to be 3,2,1 Maybe the dashed lines are supposed to represent a heatsink on that transistor?

    It's definitely happier now it's the other way around. Looking at the Peavey schematic, there is a subtle difference in the part number for Q103, it's 2SC4793V all the others on the board are 2SC4793D. 2SC4793V is only listed once on the bill of materials. Maybe it was a short production run of reversed pin out versions? Google doesn't help, I can't find a mention of it anywhere other than Peavey related things.

    The bright light bulb indication has now switched places. We have a bright bulb and Q107/Q110 heating up with HDR100 + J107 connected. HDR100 + J202 no longer cause a bright bulb.

    I think I'm making progress?

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    V means vertical. OEMs can specify lead configuration. Like TDA7293 or TDA2050 cone in H and V versions. V versions have the two rows of legs bent to the thing stands up on the board. The H version has them bent at right angles so the thing can lie flat. No difference in the part, just the way the legs are bent as supplied.

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    Quote Originally Posted by Enzo View Post
    V means vertical. OEMs can specify lead configuration. Like TDA7293 or TDA2050 cone in H and V versions. V versions have the two rows of legs bent to the thing stands up on the board. The H version has them bent at right angles so the thing can lie flat. No difference in the part, just the way the legs are bent as supplied.

    Good to know

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    I've had a little time to poke around today, I found CR100 (1N4148) shorted, it's part of the "Off Mute" circuit (very bottom of the first page), i removed it to confirm and replaced with with a through hole with its legs cut short for now. I think Q1 (J111 N-channel) might have a problem, I read 30ohms between G to D and D to G, in either direction, I'll need to remove it to test fully. Q2 doesn't test the same and has very high resistance G to D.

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    Q1 is dead, Q106 (page 1, middle right) is also dead, currently awaiting spares

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    OK I can't find Q106, an SDS-7204 this side of the pond!

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    Quote Originally Posted by jondoe View Post
    OK I can't find Q106, an SDS-7204 this side of the pond!
    I see 7204 spec'd as a 300V 10mA NPN transistor, but I have no idea why you would need such a high voltage rating for Q106, since it is on a 25V rail. There should be many TO-92 NPNs will work there. If the pinout is oddball you can bend legs around to reorient them. I'm sure someone will correct me if I'm wrong.

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    Seems like quite a meaty transistor!

    I found this Peavey transistor cross reference document;
    Peavey_Transistor_Cross.pdf

    It recommends a 2N6557 or MPS-U10, both of which I also can't source for anything less than the price of a kidney. Would it be advisable to also change Q117, so there are a pair of new transistors?

    Thanks!

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    Quote Originally Posted by jondoe View Post
    Seems like quite a meaty transistor!

    I found this Peavey transistor cross reference document;
    Peavey_Transistor_Cross.pdf

    It recommends a 2N6557 or MPS-U10, both of which I also can't source for anything less than the price of a kidney. Would it be advisable to also change Q117, so there are a pair of new transistors?

    Thanks!

    Dang - wrong part - deleted

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    Last edited by nickb; 11-21-2019 at 09:24 AM.
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    Quote Originally Posted by nickb View Post
    RS have them in packs of 100 for 8.80 for 100 https://uk.rs-online.com/web/p/products/8051129/

    You won't have to worry abut running out of them!!!!! Ever!
    Nick, that's a 6517 rather than 6557, is that what you meant?

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    Quote Originally Posted by g1 View Post
    Nick, that's a 6517 rather than 6557, is that what you meant?
    No I didn't mean that but I see what happened. I searched for the required part and it brought up the wrong one (nearest lexical match- how dumb is that?) and didn't spot it. Well spotted - thanks. Updated post.

    Can't find a decent cross for the moment. If I get time I'll try later.

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    Quote Originally Posted by nickb View Post
    No I didn't mean that but I see what happened. I searched for the required part and it brought up the wrong one (nearest lexical match- how dumb is that?) and didn't spot it. Well spotted - thanks. Updated post.

    Can't find a decent cross for the moment. If I get time I'll try later.

    Thanks Nick, I'm glad it was well past the 8pm order cut off when I saw this last night

    Would the following be a suitable replacement?

    https://uk.rs-online.com/web/p/bjt-b...stors/7613701/

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    Quote Originally Posted by jondoe View Post
    Thanks Nick, I'm glad it was well past the 8pm order cut off when I saw this last night

    Would the following be a suitable replacement?

    https://uk.rs-online.com/web/p/bjt-b...stors/7613701/

    No, that will fry. The best I came up with was an MJE340 but the pinout is wrong and it's a bit slow. Might work at a push.

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    Quote Originally Posted by nickb View Post
    No, that will fry. The best I came up with was an MJE340 but the pinout is wrong and it's a bit slow. Might work at a push.
    Just curious why you think this needs a 20W transistor?

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    Quote Originally Posted by glebert View Post
    Just curious why you think this needs a 20W transistor?

    It doesn't, but it 's the best I could find for the moment that would not evaporate.

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    The originals are 10w parts, that is why the little MPSA would burn.

    We can deal with the legs in different order by turning the part sideways.

    I still have a few 6557 as well as a coupl MPSU10, but in similar parts, I usually just find a TO220 from my stock.

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    Quote Originally Posted by Enzo View Post
    The originals are 10w parts, that is why the little MPSA would burn.
    To educate me, I don't understand how a 300V 10mA rated transistor can be a 10W device, that sounds to me like 3W or less, but I can't find any info other that that on these parts. I have never looked at one in person to know how big, etc. In this specific case, the max voltage C-E would be less than 115V, and the current should be less than 10mA (per original part spec), right? The MPSA part at 625mW might then be at risk of burning up, but 10W seems overkill.

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    The Peavey suggested replacement 2N6557 is a 2W part, were the originals just very over spec'd for some reason?

    I just found this CEN-U10, it's a direct replacement for the MPSU10, which itself is a recommended alternative part on Peaveys list. It's a little expensive per unit and a 16 week lead time on Mouser It's look like the MJE340 and hoping it fits in around the heat sinks!

    On closer inspection the one I removed from the amp was actually an MPSW42, which looked factory!

    Click image for larger version. 

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    Last edited by jondoe; 11-21-2019 at 01:06 PM. Reason: realised the one that came out was a MPSW42

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    Quote Originally Posted by jondoe View Post

    I just found this CEN-U10, it's a direct replacement for the MPSU10, which itself is a recommended alternative part on Peaveys list. It's a little expensive per unit and a 16 week lead time on Mouser It's look like the MJE340 and hoping it fits in around the heat sinks!
    Amplifiedparts has the original in stock and looks like they ship internationally. https://www.amplifiedparts.com/produ...7204-300v-10ma

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    Well I'll be damned, after looking through ebay I found some new old stock MPSW42 (10 of them), which come out at the same price as the SDS 7204 after you take shipping into account. I've ordered those

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    Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.

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    Quote Originally Posted by Enzo View Post
    Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.

    Only 3500 miles away!

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    Quote Originally Posted by Enzo View Post
    Ah. I have MPSW42 and MPSW92 in my hand as I write. Eight of each.
    Do you have various parts in candy dishes around the house for when a tech swings by to say hi? 😁
    Nosaj

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    Quote Originally Posted by jondoe View Post
    Well I'll be damned, after looking through ebay I found some new old stock MPSW42 (10 of them), which come out at the same price as the SDS 7204 after you take shipping into account. I've ordered those
    I fear those uniwatt packages will overheat and die in short order. The original is 2W in free air, 10W on a large heatsink. The MPSW42 is 1 watt, 2.5 if you can keep the case at 25C or less.

    Is the SDS-7204 mounted on a heatsink or not?

    I would go with the MJE340.

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    Quote Originally Posted by nickb View Post
    I fear those uniwatt packages will overheat and die in short order. The original is 2W in free air, 10W on a large heatsink. The MPSW42 is 1 watt, 2.5 if you can keep the case at 25C or less.

    Is the SDS-7204 mounted on a heatsink or not?

    I would go with the MJE340.
    They were not mounted to a heat sink, just folded down a little out the way from it. MPSW42 was the part fitted to the amp, even though SDS-7204 is on the schematic.

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    deleted

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    Last edited by glebert; 11-21-2019 at 08:17 PM.

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    Quote Originally Posted by jondoe View Post
    They were not mounted to a heat sink, just folded down a little out the way from it. MPSW42 was the part fitted to the amp, even though SDS-7204 is on the schematic.
    Ah! In that case you've solved that problem at least!

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    Quote Originally Posted by jondoe View Post
    Well I'll be damned, after looking through ebay I found some new old stock MPSW42 (10 of them), which come out at the same price as the SDS 7204 after you take shipping into account. I've ordered those
    I hope those are not coming from China. Those MPSW42 & 92 are now extinct, hard to find, and probably being counterfeited.

    The SDS-7024 from Amplified Parts is the same style package as those MPSWs (TO-226). I'm guessing Peavey subs on that cross-x were the next size up that could handle the power.

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    Quote Originally Posted by nickb View Post
    Ah! In that case you've solved that problem at least!
    It's not like this is the only part that got fried in the unit.

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    Quote Originally Posted by glebert View Post
    It's not like this is the only part that got fried in the unit.

    I have quite the pile of dead parts, but at least I'm learning a few things as I go

    Quote Originally Posted by g1
    I hope those are not coming from China. Those MPSW42 & 92 are now extinct, hard to find, and probably being counterfeited.]
    They are coming from a UK ebayer who has a great number of audio parts, mostly old used parts and new old stock. Fingers crossed

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