Early ‘70s Sony TA-1140/ST-1150

[Tony L]

To be honest that doesn’t daunt me. The preamp is absolutely fine, so nothing to do there for now, and I’ve already reflowed the majority of this board. This sort of work doesn’t phase me, I’ve got good tools and decent skill. I hit a brick wall fast and hard with knowledge. To my eyes the soldering looks fine, though most of the transistors have tarnished legs, so any of them could be problematic in this regard even if the joint superficially looks good.

One thing I have noticed is Q601 and Q603, which are both 2SC632A, and both have two little white dots on top, which I assume was an indicator of Sony’s pair matching, both give very different readings.

I don’t know what I’m looking at here, I don’t understand what these parameters mean, but they look very different to my eyes.

I want to swap out every transistor on this board. As soon as I’ve got a full substitution list together I’ll get an order in. The black corrosion on the legs along with discrepancies such as the above suggests they all just need to go in the bin.

 

[PigletsDad]

To be honest that doesn’t daunt me. The preamp is absolutely fine, so nothing to do there for now, and I’ve already reflowed the majority of this board. This sort of work doesn’t phase me, I’ve got good tools and decent skill. I hit a brick wall fast and hard with knowledge. To my eyes the soldering looks fine, though most of the transistors have tarnished legs, so any of them could be problematic in this regard even if the joint superficially looks good.

One thing I have noticed is Q601 and Q603, which are both 2SC632A, and both have two little white dots on top, which I assume was an indicator of Sony’s pair matching, both give very different readings.

I don’t know what I’m looking at here, I don’t understand what these parameters mean, but they look very different to my eyes.

I want to swap out every transistor on this board. As soon as I’ve got a full substitution list together I’ll get an order in. The black corrosion on the legs along with discrepancies such as the above suggests they all just need to go in the bin.

If these are in long tailed pair, that is what you want. They have very good Vbe matching (about 5mv), while Hfe matching hardly matters in a typical circuit.

 

[Darmok]

Remove all teh black leg trannys, scrape them until shiny then re-insert them.

Hmmm, bit of a nostalgic trip for me, been there, done that.

Good Luck and enjoy the ride TL

 

[Tony L]

If I can come up with a full substitute list for these eight I’d really prefer to just replace them all with new. I may be able to clean the visible area of the legs, but they are known to corrode up into the package itself. After what it did this morning I’d never be able to trust it. I really want to rebuild it to the point I’m not scared using it with my Tannoys or other rare and valuable speakers. It is potentially a really good amp, so it should be possible.

I’ve already got a recommendation for subs for the 2SC632A and 2SA705, just need the 2SA706, 2SC1124, 2SC633A, 2SA678 and 2SC634A and I can do this whole board. I have a feeling the last two are likely ok as they seem to impact the whole board rather than one channel, but I want to do them regardless. I see no logic in trying to save corroded and likely failing transistors. Just get them all out of there!

 

[Darmok]

Those soldered circuit boards may look o/k on the surface but the devil in teh detail beneath lurks headaches for the future.

 

[Craig B]

@Tony L,

Could be the lighting/shadow but R505 10k appears to have a chunk missing.

 

[Tony L]

Those soldered circuit boards may look o/k on the surface but the devil in teh detail beneath lurks headaches for the future.

I don’t understand what you mean beyond reflowing the joints, which is very easy and fast work. Are you suggesting physically removing the board and all components to ultrasonically clean it? From a vintage computer perspective all one ever does is just reflow joints if the solder looks tired or there are any cracks near connectors.

I’ve already replaced all the capacitors, replaced the six carbon comp resistors, and removed one channel’s worth of transistors. There’s only the rest of the resistors and wiring loom left!

Here’s the back of the board today before I pulled the transistors and carbon resistors. There’s a lot of dirty old flux around (I think I’m the only person who cleans up after myself!), but that aside it isn’t terrible and my fresh joints (all the caps) doesn’t seem too different looking.

If you think I should remove and replace all solder on this board it isn’t that hard. The Hakko ‘moo gun’ is amazing, just ‘moo’ and it is gone. It turns desoldering into something that is a risky chore into a two second job. ‘Moo’ and the component falls out.

The wiring looks a bit janky, but no way do I want to re-loom it! I can’t see any ‘green goo’ or obvious corrosion, but the grounds on the signal ins at the top of the board could do with redoing. I think I’ve stressed them a bit moving them out of the way when working on the board. I’ll likely remove them when it comes to replacing all the transistors (assuming I can get a sub list).

@Tony L,

Could be the lighting/shadow but R505 10k appears to have a chunk missing.

It’s just the light, it is a very shiny new Takman carbon film I stuck in. See up thread when I was puzzled (still am) by that ‘mystery resistor’ that was on the back. I ended up sticking a 10k on that channel as per the TA-3140F schematic and it noticeably dropped the DC offset. That isn’t the channel that blew today. I had stuck that back to the 7.5k that it was with the paralleled 15k resistors.

 

[Craig B]

It’s just the light, it is a very shiny new Takman carbon film I stuck in. See up thread when I was puzzled (still am) by that ‘mystery resistor’ that was on the back. I ended up sticking a 10k on that channel as per the TA-3140F schematic and it noticeably dropped the DC offset. That isn’t the channel that blew today. I had stuck that back to the 7.5k that it was with the paralleled 15k resistors.

I've been wondering if that wasn't simply one of Sony's methods of tweaking DC offset post board testing. After all, this was intended to be a premium integrated so they would likely have wanted all to be within somewhat tighter specs than were their entry level offerings. Regardless, best of luck with the fault finding.

 

[Tony L]

I've been wondering if that wasn't simply one of Sony's methods of tweaking DC offset post board testing. After all, this was intended to be a premium integrated so they would likely have wanted all to be within somewhat tighter specs than were their entry level offerings. Regardless, best of luck with the fault finding.

That is my best guess. I’m surprised they didn’t just put a trim pot in place of R505/605 like everyone else does. The service manual seems proud that DC offset isn’t something that needs setting, yet it clearly does, and that appears to be how to do it. It certainly has a very pronounced effect anyway. When ordering resistors I got a few in and around that value, IIRC I’ve got 15k as per the original 1140 schematic, 10k as per the 3140F schematic, plus 8.6k, 7.5k and 6.8k. I should hopefully be able to tune it.

There is so much I don’t understand though. I don’t even understand the basic fault-finding hierarchy. I guess the next thing I need to do is pull the right channel output transistors just to make sure they didn’t blow. I was measuring 20V DC at the output for a split second before killing the power. This obviously this morning before I pulled all the transistors out of the board. With a valve amp you power up with no valves, check the transformer, then stick the rectifier in, check voltages, and only then stick the rest of the valves in. I need to understand the equivalent transistor process so I don’t end up doing any additional damage myself. I guess it is dim-bulb tester and maybe variac from now on (I have both).

 

[Darmok]

I don’t understand what you mean beyond reflowing the joints, which is very easy and fast work. Are you suggesting physically removing the board and all components to ultrasonically clean it? From a vintage computer perspective all one ever does is just reflow joints if the solder looks tired or there are any cracks near connectors.

I’ve already replaced all the capacitors, replaced the six carbon comp resistors, and removed one channel’s worth of transistors. There’s only the rest of the resistors and wiring loom left!

Here’s the back of the board today before I pulled the transistors and carbon resistors. There’s a lot of dirty old flux around (I think I’m the only person who cleans up after myself!), but that aside it isn’t terrible and my fresh joints (all the caps) doesn’t seem too different looking.

If you think I should remove and replace all solder on this board it isn’t that hard. The Hakko ‘moo gun’ is amazing, just ‘moo’ and it is gone. It turns desoldering into something that is a risky chore into a two second job. ‘Moo’ and the component falls out.

Mmmm, yes, extract the components, scrape their legs then re-fit using fresh solder,

The atmosphere plays havoc on the microbe level in old electronic devices, a guy I worked for in his service dept taught me loads especially dil packages and their plug in sockets.

"Extract em carefully and re-sit em for peace of mind," was his motto.

 

[mik_rik]

It may be wise to replace the 2 presets.They are 50years old and will probably never been adjusted until now,They are skeleton presets and being "open" the carbon track is more likely to"dry" out and can cause problems.Most pots are enclosed for a reason.At the least give them a squirt of Servisol super 10 and work them fully a dozen times or so,and yes resolder every joint

 

[Tony L]

I’m scraping no legs! If I’m pulling any resistors out I’m putting brand new ones in! For the sake of a few tenners I just can’t be arsed faffing about. There is absolutely no budget constraint here. The amp cost me under £15 (£27 with the tuner), it is cosmetically near mint, and if I can fix it perfectly it is worth at least £350 in today’s market, likely more fully serviced (not that I want to sell it, I really want it as a spare - I like it!). The ad revenue from this thread will easily pay any component costs over the years people visit it. This is good content, exactly the sort of thing I want on pfm. This is my bread and butter!

FWIW I think the two trim pots are ok, though replacing them would be good if I can find some if the same footprint. They seemed to work as expected and hold the setting. I didn’t have any issue setting bias as per the manual. I measured it again yesterday after several hours on TV duty and it was bang on 50mV where I’d set it. Until this morning it was working great.

PS That said I really want to start by replacing all of the transistors and see where I am. I’ll reflow the whole board next time I power up the iron, but I’m just not convinced that is the issue as I’d already gone over it with a plastic tapping stick precisely to look for bad joints. I need a full substitute list. That is the first step.

 

[mik_rik]

PS That said I really want to start by replacing all of the transistors and see where I am. I’ll reflow the whole board next time I power up the iron, but I’m just not convinced that is the issue as I’d already gone over it with a plastic tapping stick precisely to look for bad joints. I need a full substitute list.That is the first step

It'll take minutes to resolder and if nothing it'll eliminate another possible cause.
The black leg oxidation can also travel down the leg into the solder joint
p.s while the amp is open, clean the fuse holders and the fuse ends
pps renew the heat sink compound on the o/p transistors and any others,preventative maintenance - speaking from experience

 

[Darmok]

I’m scraping no legs! If I’m pulling any resistors out I’m putting brand new ones in! For the sake of a few tenners I just can’t be arsed faffing about. There is absolutely no budget constraint here. The amp cost me under £15 (£27 with the tuner), it is cosmetically near mint, and if I can fix it perfectly it is worth at least £350 in today’s market, likely more fully serviced (not that I want to sell it, I really want it as a spare - I like it!). The ad revenue from this thread will easily pay any component costs over the years people visit it. This is good content, exactly the sort of thing I want on pfm. This is my bread and butter!

FWIW I think the two trim pots are ok, though replacing them would be good if I can find some if the same footprint. They seemed to work as expected and hold the setting. I didn’t have any issue setting bias as per the manual. I measured it again yesterday after several hours on TV duty and it was bang on 50mV where I’d set it. Until this morning it was working great.

PS That said I really want to start by replacing all of the transistors and see where I am. I’ll reflow the whole board next time I power up the iron, but I’m just not convinced that is the issue as I’d already gone over it with a plastic tapping stick precisely to look for bad joints. I need a full substitute list. That is the first step.

It was always my practise to scrape new and old legs of all components before inserting them into printed circuit boards just before soldering.

Not doing that, you can see problems with the flowing of solder during the process, you can see solder blobs forming + other issues.

I speak honestly with painful memories and experience.

Tis a good sign to see the copper colour beneath the components manufactured plating after a gentle scraping.

 

[Tony L]

It'll take minutes to resoder and if nothing it'll eliminate another possible cause.

Yes, I’ll certainly do what I describe as a ‘reflow’. My normal approach is to just reheat the joint until the solder reflows, and if it looks a bit janky suck it and add some fresh. Common practice with vintage computers, especially around chip DIL sockets and card edge-connectors, interface sockets, power supply inputs etc.

 

[Tony L]

Just trying to coordinate transistor knowledge into one place:

2sc632a check out siliconarc 20 for £3 (minimum order£10)
2sc633 - bc168 -bc 183 - bc328
2sc634 - bc167 - bc182 - bc237
2sc1124 - 2sc1913 - 2sc2384 - 2sc2481
2sa705 - bc640 Cricklewood?
2sa706 - ksa1220 bd416 - bd416 - bd508 - bd516
This is a not an exhaustive search and some transistors may now be obsolete also and I have not checked pin out connections , hope some of this maybe of use.
Also double check anything on the list !

KSA1015. KSC1815 are 50V like the originals and centre collector pin, similar Ft, so should be stable. RS sell them

And here’s a thread at AudioKarma, it’s a different amp, but a couple of transistors are the same:

Sony TA-5650 transistor alternative list

Sony TA-5650 transistor alternative list (Updated) Could be some help to some TA-5650 and Ta-4650 owners. Since the most original transistors are no longer available, these could be good alternatives, the most are picked from the Transistor Substitution Data Book 1993. I picked them also by...

audiokarma.org

I’m confused as hell. I have no idea what to order, I just want a shopping list I can buy from RS or wherever! I have no idea how to choose when there are several options. I’ll happily buy them all, but I’d then not know which to put in the board!

When there is a list like BC168, BC183, BC328 etc are they all exactly the same like say a 12AX7, ECC83 or CV4004, and can be used in the circuit without any other changes, or is one more suited in some way than the others? I really need to understand this, or more accurately I don’t, but I do really need to know what to order!

 

[mik_rik]

In most cases they will be similar or higher spec, quieter or faster ,higher current/voltage handling,gain etc
Have a look at Audio Karma Pioneer sx-1250 restoration threads,there are quite a few,which do lists of
transistor replacements,a lot of these are common to your amp

 

[Tony L]

In most cases they will be similar or higher spec, quieter or faster ,higher current/voltage handling,gain etc
Have a look at Audio Karma Pioneer sx-1250 restoration threads,there are quite a few,which do lists of
transistor replacements,a lot of these are common to your amp

There’s a very substantial substitution list for download in post #3 of this AudioKarma thread.

Sony transistors in amplifier - updated replacement question

Hi - Currently working on a VFET TA-4650 integrated. All is going well so, Im doing the usual mods for safety. One question is the small signal transistors. I had some wild DC offset at the speaker terminals - approx 100mV per channel. Replacing the differential pair 2SA705 in both channels...

audiokarma.org

The relevant ones for me are:

2SA705 → KSA992
2SA706 → KSA1381
2SC632 → KSC1845
2SC633 (none listed)
2SC634 → KSC1845
2SC1124 → KSC2690
2SA678 → KSA1015

Do these look any good? Does the ‘A’ suffix matter, all the 2SC63x in the TA-1140 have an ‘A’ at the end. I’m also missing a 2SC633A substitute.

PS This is such a PITA compared to valves. What the hell went wrong? I could have rebuilt a Stereo 20 in the time I’ve spent looking at bloody lists on the internet, and I’m still none the wiser!

 

[Darmok]

PS This is such a PITA compared to valves. What the hell went wrong? I could have rebuilt a Stereo 20 in the time I’ve spent looking at bloody lists on the internet, and I’m still none the wiser!

That's IT for you.

 

[Tony L]

Here’s another sub list from someone’s rebuild of a TA-1066

2SA705 → KSA992F
2SA706 → KSA1220A, TTA004B
2SC632A → KSC1845F
2SC634A → KSC945CG, KSD1616A
2SC1124 → KSC2690A, TTC004B
2SA678 → KSA1015, KSA1013

The thing I find so frustrating is the lists don’t fully align, so I still don’t know what to buy. These have suffixes so I assume are possibly closer?