Technics SU-VX800 amplifier

JoeJester

Joined Apr 26, 2005
4,360
Ok....to help you a little for local sources ....

You can replace the 2SA1265 with the 2SA1106, 2SA1146, 2SA1186, 2SA1301, 2SA1302, 2SA1303, 2SA1386, 2SA1386A, 2SA1386A-O, 2SA1386A-P, 2SA1386A-Y, 2SA1491, 2SA1492, 2SA1516, 2SA1695, 2SA1805, 2SA1941, 2SA1942, 2SA1943, 2SA1962, 2SA1986, 2SA2120, 2SA2121, 2SA2151, 2SA2151A, 2SA2151A-O, 2SA2151A-P, 2SA2151A-Y, 2SB1429, 2SB863, FJA4210, FJA4213, FJL4215, KTA1943, KTA1943A, KTA1962, KTA1962A, MJW1302A, MJW1302AG or NTE2329

You can replace the 2SC3182 with the 2SC2581, 2SC2706, 2SC2837, 2SC3280, 2SC3281, 2SC3284, 2SC3519, 2SC3519A, 2SC3519A-O, 2SC3519A-P, 2SC3519A-Y, 2SC3855, 2SC3907, 2SC4468, 2SC5198, 2SC5199, 2SC5200, 2SC5200N, 2SC5242, 2SC5358, 2SC5948, 2SC5949, 2SC6011, 2SC6011A, 2SC6011A-O, 2SC6011A-P, 2SC6011A-Y, 2SD1148, 2SD2155, FJA4310, FJA4313, FJL4315, KTC5200, KTC5200A, KTC5242, KTC5242A, MJW3281A, MJW3281AG or NTE2328

Source:
https://www.el-component.com/

Or you can read the datasheet and find a replacement with better specifications.

whatever the transistor you find locally, go back to that website and replace the partnumber in this address with the one you find. On that page you will find the compliment to the selected transistor.

https://www.el-component.com/bipolar-transistors/2sc3182

Shows the compliment of the 2SC3182 as 2SA1265 ... which are the exact transistors in the faulty circuit.

If you have any questions .... you know where to find us.

on edit ...

I know your tester also displays the hfe. When you checking them, make sure the hfe is within normal range as well. The hfe is also listed on that website for the transistors.

The 2sc3182-R should be 55 to 110.
 
Last edited:

JoeJester

Joined Apr 26, 2005
4,360
On EBAY, in fact, there are quite a few sellers who supply these fake Toshiba transistors.

True. I don't know Marius' location. however, there are a number of reputable online stores like Newark, Mouser, Digikey here in the U.S. And I just can't recall the one's in the UK right now, or the one in Australia. If we think it could be a source of supply problem (ebay) it would be wise to try elsewhere.
 
Last edited:

JoeJester

Joined Apr 26, 2005
4,360
I should have mentioned this earlier, blowing up that 4 amp fuse also demands one to check the integrity of the diode bridge, D601. I don't think there was any damage to that 25A bridge you installed, but Id check it out as well.
 

Thread Starter

Marius83

Joined Dec 28, 2017
380
What does BLOWN mean? I realize it means NO GOOD, but let's get down to how they failed. SHORTED (b-c, b-e, e-c) OPEN (b-c, b-e, e-c)
In lieu of waiting for those components, try to get the substitutes for them that are locally.


You described a blown fuse AND R513 smoking. A circuit oscillating could have overdriven those four components. The challenge is to explain all those conditions. So, please inform us of how each transistor failed.

Don't forget to get a replacement for R513 if you measure it out of specifications.

My later observations is that R513 did not smoke, and measured ok out of circuit.
There are two 2A main fuses at the power switch, these two did blow.

I have tested the power transistors now, look at two of my pictures, just to illustrate how my tester shows it.

Here are what my DMM shows at diode testing setting:

Q507
Red to B

Black to E: OL.
Black to C: .008 V

Black to B
Red to E: OL.
Red to C: .008 V

Red to E
Black to C: OL.

Black to E
Red to C: OL.

Q509
Red to B

Black to E: .002 V
Black to C: .002 V

Black to B
Red to E: .002 V
Red to C: .002 V

Red to E
Black to C: .002 V

Black to E
Red to C: .002 V

Q515
Red to B

Black to E: .002 V
Black to C: .002 V

Black to B
Red to E: .002 V
Red to C: .002 V

Red to E
Black to C: .001 V

Black to E
Red to C: .002 V

Q517
Red to B

Black to E: .002 V
Black to C: .002 V

Black to B
Red to E: .002 V
Red to C: .002 V

Red to E
Black to C: .001 V

Black to E
Red to C: .002 V



Q5.jpgQ54.jpg
 
Last edited:

Thread Starter

Marius83

Joined Dec 28, 2017
380
True. I don't know Marius' location. however, there are a number of reputable online stores like Newark, Mouser, Digikey here in the U.S. And I just can't recall the one's in the UK right now, or the one in Australia. If we think it could be a source of supply problem (ebay) it would be wise to try elsewhere.
If the transistors i have bought would cause problems, i should get the problems in the RIGHT channel to, transistors from the same seller sits there... :rolleyes:

I have bought from Ebay, China... there are some of these transistors for sale with a much worse print on, which i have not bought because they looked like real counterfeits, hehe.. but the ones i have bought might also be, i don't know, see pic.

I am located far up north, in Norway, but shipments from Digikey arrive just in a few days, i guess i will look for replacements on that site, if we question the quality on the ones i have bought earlier....


toshiba.png
 
Last edited:

Thread Starter

Marius83

Joined Dec 28, 2017
380
@JoeJester: Doesn't seem to show the HFE, see the picture.. might be an option to be changed in the menu...hmm


About power transistors, i actually have four that tests OK!
Some has been in circuit earlier, but removed just to get four with the same "look".. hehe.... maybe some are counterfeits... i guess they'll do ?

Q555.jpg




Q505.jpg
 
Last edited:

JoeJester

Joined Apr 26, 2005
4,360
Up by Bo? That's probably the furthermost northern city I know of in Norway.

It's pretty easy to see when you place a total of 120V across 0.44 ohm resistors, the fuses had to go. I'm glad R513 didn't suffer any damage. I'm sure it got plenty warm with a few shorted C-B on both rails.

Something caused those others to have that problem ... unless ... they were substandard.

With the four failed transistors out, we may need to look at the base and emitters of Q503 and Q505 with the to ensure there is no sustaining oscillations. But hold off on that for a bit. I need to think a little more, but the other two may have a good reason for that type of failure. It is time for further checking.
 
Last edited:

JoeJester

Joined Apr 26, 2005
4,360
Marius,

hfe is the B on your tester (beta). Beta is the DC current gain and hfe is the AC current gain.

ICE0 and ICES are leakage currents and should be zero.

Your mk328 TESTER indications look correct for the conditions you measured with the dmm for those two transistors, Q507 and Q509.

You might even get the same resistance readings if you measured them using the ohms on your dmm.

Here's how I viewed your test results:


tests.jpg
 
Last edited:

MrChips

Joined Oct 2, 2009
21,856
Check all the resistors in the 5xx section.
R501, 3.3kΩ
VR403, 500Ω
R465, 1kΩ
R503, 18kΩ
TH501, 100kΩ @25°C

R509, 680Ω
R511, 680Ω
R513, 330Ω

R515, 2.2Ω
R517, 2.2Ω
R565, 2.2Ω
R567, 2.2Ω

Leave off Q507, Q509, Q515, Q517

Power ON and measure voltages at the following and compare with factory voltages:
R503
R509
R511
R513

(I know we've climbed this hill before. Something looks suspicious around VR403 and TH501, just thinking aloud.)

Edit: Replace R513 even though it measures ok.
If for some reason R513 goes high or open it will cause the failure you experienced.
 

Thread Starter

Marius83

Joined Dec 28, 2017
380
@MrChips.

The power on test you described, should i install Q503 and Q505 first?
They are out at the moment.
Should i also check Q501 (?)

Looks like all the resistors have survived...

R501(3.3KΩ): 3.26 KΩ
VR403(500Ω): 540 Ω at minimum setting (in circuit)
R465(1KΩ): 987 Ω
R503(18KΩ): 18 KΩ
TH501(100KΩ25°C) 148 KΩ 13°C

R509(680Ω): 674 Ω
R511(680Ω): 677 Ω
R513: will install new
R515(2.2Ω): 2.3 Ω
R517(2.2Ω): 2.3 Ω

R565(2.2Ω): 2.2 Ω
R567(2.2Ω): 2.2 Ω
 
Last edited:

JoeJester

Joined Apr 26, 2005
4,360
Ok... the resistors looks good even the thermistor ...

Here is the calculated value for three different thermistors for 13C.

CALCULATIONS.jpg

Here is a graph from 0 to 105C using those same three values ....

GRAPH.jpg

I'd say your thermistor is ok.

And finally, the %error for your readings.

Resistances.jpg

The formula used for the graph and calculation of the thermistor came from Murata

Here's a Log-Lin graph .... it may be easier to estimate the resistance ... from the simulator.

Simpulation.JPG
 
Last edited:

JoeJester

Joined Apr 26, 2005
4,360
I have a question, and maybe @Technics44 can provide some insight. Does the higher power transistors in this set or any component in this set use thermal grease or mica for isolating them from the heat sink electrically? I mean the transistors I see in the pictures the collector is the tab. That can open up a whole new possibility to ensure the heat sinks are isolated, and that only those connected to the same rail share the same heatsink.

I'm of the ilk that there has to be all logical reasons for these failures are addressed before installing another set. I await the results of the second part of MR Chips test request.

From the information so far, the "counterfeits" hypothesis is gaining ground as they typically do not meet published specifications for that type of device.
 

MrChips

Joined Oct 2, 2009
21,856
I find it strange that all four power transistors, Q507, Q509, Q515, Q517, would blow.
I still need to look at the simulation. It would appear that something went wrong in the preceding stage, the driver amp.

Yes, install Q501, Q503, and Q505.
Check voltages are all three transistors.
 

JoeJester

Joined Apr 26, 2005
4,360
I find it strange that all four power transistors, Q507, Q509, Q515, Q517, would blow.
I still need to look at the simulation. It would appear that something went wrong in the preceding stage, the driver amp.
I wholeheartedly agree. Three out of four shorts is certainly unusual to say the least. The interjection of poorly spec'd transistors is certainly a thought.
 

JoeJester

Joined Apr 26, 2005
4,360
On this amp the power transistors are isolated from the heat sink by micas on which there is thermal grease.
That is what I thought was typical. In addition are their insulators for the screw hole?

Now we have to see if Marius used such items, I do see a slight trace of thermal grease on the two transistors that looked like they were removed from the circuit.

It's just another thought towards the resolution to this problem by eliminating everything possible.
 
Top