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Almi's Logitech Z-5500 Mod (High-End upgrade for the speaker system) - Page 7

post #91 of 400

Hi, @jayjayuk


Glad to see that you got another board to experiment with. It is good to have one spare! :smile:  About the regs from that china guy, that is too much money spent for me, this mod cost me already bunch of money, and don't wanna spent extra. Instead i am going to search for alternative replacement of the reg if they are really faulty. But thanks anyway.  :beerchug:   And i just discovered that the pod freezing even without any signal put in. Just switched on!!! And the system make that little "pop" sound when switching on, even at volume set to 0, and without any cable plugged in the pod. Is this normal? I don't remember, be like that before(i mean before all mods i have made)  Unfortunately, left the multymetter in work, and can't measure if the regs put correct voltage. @ramachandra  said i can use L7818CV and L7918CV , but they are pulling 1A out, not 500mA like originals. I wonder if that would be a problem? I can order exact model for positive, but negative one is really hard to find even L7918CV! 



post #92 of 400

yes i could find the positive one easier than the negative... when you say just switched on and it make a pop... do you mean when you had the pod connected or when it was bypassed? if when it was bypassed then you could hear a pop from the main switch being toggled as the amps are instantly turned on and off with the main power switch... the pod is responsible for the on delay of the amps as so any interference from switch is not picked up when turning on and off... if it does it when using then pod then i am not sure... i never noticed mine pop when i used the power button on the pod.


if you have a datasheet for the 78ma18a and the 79m18a that is used the z5500 can you please send me it as i can not find it online... even sellers online that i have seen say no datasheet for this item?




EDIT: at the minute i would not mind a couple of pops out of the sub to be honest haha

Edited by jayjayuk - 6/21/14 at 11:33am
post #93 of 400

http://www.ic-on-line.cn/view_download.php?id=1678317&file=0340\ts78macpr0_2296562.pdf,  http://www.alldatasheet.net/datasheet-pdf/pdf/217320/TSC/TS79M18ACPRO.html   here thanks to @ramachandra! I noticed that the little "pop" sound appears only when analog input is selected, and also i didn't noticed ever before,because using only digital, but there is a very audible noise from the speakers, in analog.

post #94 of 400

@ramachandra i have found a resistor at r623 which should be 100R but it was reading 220R ... i checked on the other board i had and it was reading 100R and the markings also said it was a 100R (01A) which is on the sub op-amp -18v in so i swapped it for the one off my other board... its in and reading 100R... but i have a problem... on around the op-amp U15 there is a resistor R618 which is marker 2606 ... the calculators say its a 260M ohm resistor and working it out also says 260M ohm ... but when i test both of mine on both boards they read 90K ohm should i leave them or should i suspect they are both bad and get some more to change them.


also i only checked the smd's right near the op-amps not near the caps... so i am checking everything i can now and using this other board as a parts board for now. just dont know what to do about the 260M ohm resistor where both are reading 90K with tight tolerance between them... any input would be appreciated.

post #95 of 400

So, little light in the tunnel!  :smile:  Today i get the multymetter, and check pre amp board again. And all the resistors was gone! All not reading resistance. So guess thats the problem. Tomorrow i am gonna get some from local store. I am hoping that running system this way for a while didn't broke something else. And guessing that the voltage reg also overheat because of that! Crossing fingers! I checked the resistors with calculator, and there is 6x10K Ohm, 3x200K, 1x100k and one that is with only one black stripe, that i cannot check! 


This one under! Can you give me the info, please ? All resistors are +/- 5%, but in my store there is also wattage, and i don't know what wattage are they. Also for 200kOhm, in my store are only 220K. Is this be a problem? Also is the more wattage be a problem or benefit in any way?



Edited by andro6600 - 6/22/14 at 9:49am
post #96 of 400
Thread Starter 

At least one of the pin of the component need to be disconnected from the board to get proper readings about resistance, capacitance ect.




I'm not familiar with the codes used for them. If the two boards you have identical, comparing the readings sped up the job and probably no need to desolder.




I do not know how many watts the resistors are on the preAmp board. Judging about the size 1/8W. To be on the safe side use 1/4W. No need to worry about tolerance, this is not a precision measuring equipment. The resistor with the single black code is a jumper wire, because the machine installed the components can not handle plain wire, so it is shaped as a resistor.


The voltage regulator from Farnell is looking good. The junction temperature is not necessary the same as operating temperature as much as i know, and somewhere else i found the original reg have the same operating temperature.

For example the 1A only mean the regulator can handle it, and not mean it is drawing it from the psu. If the power requirement go beyond the limit is when the problem staring for the reg.


Here is some information why and how components are fail and why the damages are irreversible:


post #97 of 400

@ramachandra , so basically i can solder bridge wire on the place of one striped resistor? Good. I pulled off  the resistors from board, and they still read nothing! Other resistors have the value, even on the board, and the faulty ones lost the outside cover from both sides. So they are dead for sure. Also, just for insurance, i am gonna order that voltage regs from farnell, if you said that they are compatible, just in case old ones still overheating.


Lol, this mod gonna teach me a lot about electronics! I am going to make a Masters degree!  :smile:



post #98 of 400

@andro6600 that 1 X 100k you have there is wrong... i have it down as a 100R and i have had all mine out and tested original with multimeter ... the original resistors are 1/8w carbon... i have changed all of mine for 1/4w metal film... no bad done by going up wattage as long as they still fit ok... they just dissipate heat better and therefor can resist more current before failure. as @ramachandra said the one with a black stripe is just a jumper wire.


here is the list i did for them when i first calculated them by colour... then took them from preamp board one by one... measured resistance and if my first calculation was wrong i would look at the color again and see where i went wrong...


6 X 10K 1/8W 5% (brown,black,orange,gold)
3 X 200K 1/8W 5% (red,black,yellow,gold)
1 X 100R 1/8W 5% (brown,black,brown,gold)


the other resistors are...


7 X 2.2R 1/2W 5% (red,red,gold,gold)

2 X 36R1/4W 5%   (orange, blue, black, gold)


5 X 2.2R are on the pre-amp board behind the new caps you just put in.

2 X 2.2R are near the tda amps for the sub (near the main filter caps).

2 X 36R are the ones at the +-18V regulators


i think i found the problem with my setup... i have not been using the 2 center screws that center the board and as i clamp one side to the heatsink and then the other side... there has been a big gap on the second side (between tda amp and heatsink) because of the first clamp pulled the board over... so on one tda (the sub and a left rear) it had broke the pins on the tda amp on the sub tda all the long pins had no continuity from the bottom side off the board to where they enter the tda chip... so about 8 pins on the sub tda and about 4 pins on the left rear... so i am waiting for my tda's to turn up from china (seems like its taking forever) but its a big relief as i am pretty sure that i will have had those op-amps in right (at some point) but it was the tda at fault... i am pretty certain when i get new tda's in it will be a runner again :)


@ramachandra yes both boards are exactly the same so from one to another is easy... even if i cant get a good reading on something then there will be a patter... like a steady rise and then sit at a resistance... although not perfect... it is a good reference as if it sits at another reading there could be something work checking up/down stream from that point. makes it easier... and that resistor i have changed it... i will just get my main system up and running again and then i will get some smd's in and replace the ones i have taken from that board... i took the 2606 out and it still was reading 90K so i will just replace with 90K


the tda amp was the find off the day for me... will center the board from now on.

post #99 of 400

@jayjayuk, it seems that totay is a good day for both of us, finding the reasons for the problems! :smile:  Yes, you are absolutely right about the resistor, i was mistaken. It is very helpful to have all the resistors values. Thanks! I decided to replace all the caps in control pod, that @ramachandra didn't mentioned, with Panasonic FC/FM series,but doubled the voltage of the originals, just for good sake, if not to make any big difference in sound, just to be shure, that they are good quality, and more reliable. 

Edited by andro6600 - 6/22/14 at 1:04pm
post #100 of 400

@andro6600 i am not sure but i think i might know what your problem is... i did this once lol... i was showing my system off to someone and had the pre-amp board out and it shorted the d-sub pins to ground heatsink... at this point it fried the -18v resistor near the -18v regulator... the resistor went from 36R to 30R and the sound would play for like 10-20 seconds and then stop... after i changed the resistor all was fine again... maybe you should take both 36R resistors out and check with test meter. as my resistor did look dark like yours and only when i took it off was there a piece of casing missing from the bottom and the test meter said it was reading 30R so i changed... other than that it just looked a little dark... i had a resistor on the other board look worse than that with lots of the casing missing and it still read 36R so definitely need o take them off and have a look at them. if you are going to replace them then i would put in 1/2W 36R i only used 1/4W because i already had them from a big pack of lots of values that i bought.


also... the blown track you have on the pre-amp board... i have a second board (which as of now if it works... is the good board lol practice makes......... a mess haha) which the same track had blew out on... but this was because again... on initial testing to test what was working (in the end only center so i ripped everything of the board and waiting for new parts) i again shorted the pre-amp board (must learn to tie pre-amp board down!!!) but it was to the square silver bridge rectifier (as there was no heatsink and it was just on my bench with transformer hooked up... this made a big spark and when i had looked what had happened it had burnt that track from the board... so i wonder what happened to yours for you to burn that track out as its not really a small track?


for my system i have ordered some more tda amps from the UK... i removed 4 all together from my main system... i am not waiting for china any longer so i bought some from UK which should turn up in couple of days.



post #101 of 400
@jayjayuk, this looks like exactly mine case. Now that you've mentioned, i will replace and the voltage resistors as well. They cost nothing anyway. So, what you suggest, metalized or carbon casing?

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post #102 of 400

personally if i am changing it anyway... i will go with metal film 1% and go up a wattage size so in this case i would get 1/2W metal film 36R 1% for the v-regs (as long as i can still get it in nicely)...

if you get the two 36R resistors out and then check them... if something is wrong then change them... the stock carbon resistors can read anywhere from 34.2 --> 37.8  where as the metal films will read between 35.64 --> 36.36 ... so the metal films are closer to the resistance... i know if those resistors drop to 30R than you will see problems as i did. personally i would just try changing both resistors first and then run the system and keep checking temp on v-regs to see if they are any better... if not then change the v-regs... its strange that yours you say are running very hot with no pod connected... like i say mine run cold... if when you change then they still run hot then maybe there is a problem somewhere else on the amplifier board? or maybe this heat is to be expected? when my tda's turn up from china i will know more as i will have two systems to compare against.



post #103 of 400

@jayjayuk, you were right man.Thanks!  :beerchug: Indeed the problem was in regulators resistors. First, i changed the pre-amp board resistors, and tried, but no luck. Then i opened the whole amp board again( man i am sick from that :smile: ) and desolder resistors, checked them, and they was reading 36 Ohms, but change them any way. I bought the 0.63W metalized 1% resistors for all positions. And "Oh miracle" The system is up and running for more than 1 h 30 min without stopping!!! YESSS! Voltage regulator are still extremely hot. I ordered bunch of different kind regs:







So, my wondering is, to replace both, but i see the TS7918CZ pins are placed differently from original 79M18A, pin 2 is input and it is said that this is connected to pad?! Original one have ground at pin 2, witch is connected to pad? How is that possible? 


EDIT: BTW, what are caps in pre-amp panel are for? The five caps obviously is for speakers, but remain two?

Edited by andro6600 - 6/23/14 at 11:07am
post #104 of 400
good to hear you got it sorted smily_headphones1.gif or running continously again at least. i realized when i had ur pic up... i was mainly looking at vregs... but then i noticed discoloured resistor and it rung bells lol. when u get those regs and try them please post what works well and what does not. not sure about pin config but if comparing the pins on datasheets is not the same then i would say not to put that one in. not sure what those caps are for @ramachandra might know what they do... i have not really started tracing tracks yet but i am very close to doing so.
post #105 of 400

Here, the schematic of pre amp panel

Unfortunately the TC7918CZ is the only negative regulator that i can find... But @ramachandra said that it is compatible if i understood him right... Also if you said that yours are overly hot, than maybe it is normal.... Beats me!

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