Working on a Ti 1200.1

Post by **Jacampb2** » Thu Oct 02, 2008 2:36 pm

I bought this on ebay for about $250. The guy said it had a small burnt spot in the corner of the board. I got it here, and it had a hole burned through in the power supply of the left amplifier section. It came missing the isolation plate for that side, both fans, and all hardware. I was not really impressed, but am trying to fix it anyhow. So far I have not found why the power supply shit the bed, but once I get it back together I will be able to check some more things.

I cut out the burnt section of board, I made a patch and soldered it using some solder braid to bridge the board sections. The side that does not have a connection is super glued

It is very secure. I cut the minimal traces by hand with a file.

Here are the pics. I did not have any 30 ohm smd resistors, so I put some through hole ones in temporarily. I should know later tonight if she is going to come alive or not.

Later,
Jason

Post by **Jacampb2** » Mon Oct 13, 2008 4:32 pm

Its all fixed. I never did find what caused it to burn in the first place. I think it is possible that someone spilled something in it. I found a lot of liquid residue on the board, enough that I thought one of the caps had leaked. I checked them all out though and there was no problem. I rebuilt the power supply, and all is well. It sounds great. I still have to run it for a few months to make sure it has no intermittent problems.

I have the proper screws coming in, but in stainless. I will also match the isolation plate eventually.

Pics:

Later,
Jason

Post by **Rold Gold** » Mon Oct 13, 2008 4:37 pm

DOOD!!!!!!
That's pretty sweet!!!!!! Nice score too.......

Post by **stipud** » Tue Oct 14, 2008 6:50 am

Nice fix dude! I would have given up at square 0!

AaronK · Post by **AaronK** » Tue Oct 14, 2008 9:08 am

man seeing stuff like this makes me want to go back and get my EE. Sweet!

Post by **Jacampb2** » Tue Oct 14, 2008 4:05 pm

FuzzyHoNutz wrote:Nice score too.......

I don't think I would take things that far. I didn't post much here about it because no one seemed interested, but on top of having to purchase all the mounting hardware, as well as two new fans, I also got the complete pleasure of doing the power supply twice.

I put it back together after patching it up and I promptly smoked the power supply FETs again. This time it was my fault, I had one of the resistors I had cobbled in there touching the +12 plain that was uninsulated from my repair. It switched all of the fets on when power was connected, and caused a fair amount of collateral damage. I should have waited, as I had the SMD resistors on order, they were there in a few days, and it turns out I had to wait for them anyhow, because I more PS FETs in the order too.

All in all, I have probably $400 into it, not including time. All the little BS adds up. I think to get $400 back out of it would likely be pushing it w/ the repair. Not that I want to sell it, but I like to have the potential to break even if I have to, ya know?

Later,
Jason

vingasoline · Post by **vingasoline** » Tue Jun 23, 2009 6:47 pm

hey I got a question for you.. there are 2 transistors??? above the bank of fets where the repair was made, in sot223 packages. The markings on it say FD219, A5G << any idea what those are?? reason I ask is because I have a 1200.1 that turns on when power/ground is hooked up, and off when remote is turned on.. cause is a blown one of those< in a different location on the board. I cannot find a match for that part # anywhere..

Post by **Jacampb2** » Tue Jun 23, 2009 7:10 pm

The part is a common A56 small signal transistor not a A5G, that is your problem

The pair is A06/A56, I can look you up a part number at digikey or mouser if the above is not enough

Good luck,
Jason

vingasoline · Post by **vingasoline** » Tue Jun 23, 2009 7:38 pm

thanks for the reply. The only part I can find is PZTA56, and it says that is a pnp transistor.. I am pretty sure the one on the amp is a npn transistor. am I wrong?

Post by **Jacampb2** » Tue Jun 23, 2009 9:17 pm

PZTA56 is correct, I believe that is the fairchild semiconductor number for it. PZTA06 is the number for it's NPN compliment. I could not tell you for sure which you need, as the drivers you asked about are used in matched pairs, both a56/a06. If you tell me the component # off the board, I will see if I can find it in my amps and let you know for sure. It will be labeled Q###.

BTW, I believe mouser is the only big online distributor that stocks the sot-223 packaged ones.

Later,
Jason

vingasoline · Post by **vingasoline** » Wed Jun 24, 2009 4:42 am

Q91, located between B- terminal and sg3525ap.. thanks for your help

Post by **Jacampb2** » Wed Jun 24, 2009 4:09 pm

Q91 is definitely PNP, A56. Q90 is it's NPN counterpart in the remote circuit.

The way it works is this: When the remote goes high, it saturates the base of Q90. Q90 is at ground potential on the emitter side. When it saturates, it's collector, which is tied to Q91's base, pulls Q91's base to ground-- This causes Q91 to conduct. Q91 is situated between the B+ supply and the amps switched 12V supply. When Q91 conducts, it energizes the switched 12V supply. If Q91 is leaky, it will conduct, or partially conduct all the time. I would replace both Q90 and Q91 if I were you, even if Q90 still tests good.

Later,
Jason

vingasoline · Post by **vingasoline** » Wed Jun 24, 2009 5:39 pm

any idea what part # will replace Q90.

Post by **Jacampb2** » Wed Jun 24, 2009 5:42 pm

PZTA06 is the SOT-223 packaged one. $.25 at mouser. Kind of a ridiculous price IMO...

vingasoline · Post by **vingasoline** » Wed Jun 24, 2009 7:12 pm

this is where im confused. on my board, Q90 is very tiny. rectangle, has two leads on one side and one lead on the other. I believe the markings on it are P16

Post by **Jacampb2** » Wed Jun 24, 2009 8:29 pm

does it look like this?

If so, it is just the sot-23 package. I will verify when I get home.

Later,
Jason

vingasoline · Post by **vingasoline** » Wed Jun 24, 2009 8:52 pm

yes. so that is a sot23 A06

Post by **Jacampb2** » Wed Jun 24, 2009 10:40 pm

vingasoline wrote:yes. so that is a sot23 A06

It should be, but I can't guarantee anything... I will try to remember to check mine when I get out of work this AM.

As for reading the markings on SMD parts, I have a big lighted positionable magnifier, and I also have to sometimes resort to a 15x jewlers loupe. Either one is well worth the investment. I expect that you can pick up a cheap loupe on ebay. It makes life easier...

Later,
Jason

Post by **Jacampb2** » Thu Jun 25, 2009 6:16 pm

Sorry for the late reply. I got blind sided with a whole bunch of crap when I got to work tonight. The Q90 is a SOT23 A06 npn transistor. It is marked "p1G", which crosses to A06. For some reason they are marked in code instead of with the part number. Funny, but if p1G fits, then damned if A06 shouldn't have been able to fit. Anyhow, I have a screen shot of the cross ref. I will post it up later when I have some free time.

Later,
Jason

vingasoline · Post by **vingasoline** » Thu Jun 25, 2009 7:11 pm

don't worry about the screen shot. I believe you.. thanks a lot for your help. Now I can stop pulling my hair out and get this thing fixed.. I can't believe I missed that A5G = A56. hard to see without magnifying.

Post by **Jacampb2** » Fri Jun 26, 2009 9:43 pm

vingasoline wrote:don't worry about the screen shot. I believe you.. thanks a lot for your help. Now I can stop pulling my hair out and get this thing fixed.. I can't believe I missed that A5G = A56. hard to see without magnifying.

I already had the shot, may as well post it

I am still at a loss as to why they didn't just lable with the part number-- maybe because there are some 4-5 digit part numbers and since those won't fit, they just code them all to 3 digits so there is no confusion...

Here is the excerpt for the cross reference:

Later,
Jason