Sony TA-88 - UK Vintage Radio Repair and Restoration Discussion Forum

humphrey · 20th Dec 2017, 5:29 pm

Been a while since my last visit. Thought I would use my old Sony as a PC CD amplifier. Last night I left it switched on and was awakened by what sounded like the cats were smashing up the catflap.

I turned it on the next day and it sounds just the same.

Left channel was causing the noise with the right channel still working.
The left channel was not responding to the volume control being loud through the range. With the left speaker disconnected the right channel is working ok but with slight crackling. I have two of these amps with the last one traveling around the globe with me when I was in the Merchant Navy.
I understand that some of the transistors used in these sets were not entirely up to the job. Not being very good at tracing faults, I would like to replace these suspects - if I knew what they were.

Grubhead · 20th Dec 2017, 6:46 pm

When you have one channel playing up then I always compare readings and just looking at them to see if there is any difference. As both channels use the same parts. You just identify which channel is which.
You can't really go on what might cause a problem, because electronics don't behave like that. The big trouble makers might be working fine in your model. The ones that don't normally cause the problem could be the culprits.

Diabolical Artificer · 21st Dec 2017, 7:26 am

I know the amps you mean, had a few friends had these back in the 80's, they were popular in bedsits.
Service manual available here - https://www.hifiengine.com/manual_li...ny/ta-88.shtml

Andy.

humphrey · 21st Dec 2017, 11:21 am

Is an oscilloscope and signal generator any use here as although the voltages on the schematic are showing normal, it does not account for the noise on the left channel. It will be nice to use those items of equipment that have hardly been used.

humphrey · 21st Dec 2017, 12:51 pm

It might be worth mentioning that that the unit is pre modification with the 315ma fuses but the resistors are according to the mod and appear to be original.

orbanp1 · 21st Dec 2017, 3:36 pm

The Sony TA-88 has some design problems.
See this thread, and especially posting #6:
https://www.vintage-radio.net/forum/...highlight=ta88

Regards, Peter

humphrey · 21st Dec 2017, 7:10 pm

So far I have not found any deviations from the schematics. However I have another TA88 that has no output at all. There are some odd voltages on a couple of transistors. They are Q101 and Q102 2SC631A and 2SA704. Are equivalents available?

orbanp1 · 22nd Dec 2017, 5:55 pm

There are fuses at the speaker outputs, do check those.
Also check the rail voltages.
If the speaker fuse was blown, do measure the DC output voltage without any input signal before you attach the speaker to it, the DC output voltage should not be more than a few 10mV!
If it is significantly more, then probably the final and/or driver transistors are blown.

Q101 and Q102 are part of the RIAA pre-amp for the phono input, if that is the only fault, then the amp should still work OK with the other inputs, like "tuner", and "aux".
Do a search for low noise audio bjt transistors, or go to the diyAudio.com, solid-state subforum, this has been discussed there ad nauseam.

Good luck, Peter

humphrey · 23rd Dec 2017, 11:59 am

I just got my dead set going on one channel with no noise. At least I can compare them. I had to replace a crusty old 100mF cap in the power supply. I am thinking that I should really replace all the e caps because of their age.
I could not find any dodgy transistors.

humphrey · 13th Jan 2018, 3:26 pm

Changed all the E caps and it now works fine with no crackles either. Now to get the second one done. Luckily all the transistors were ok.

20th Dec 2017, 5:29 pm	#1
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Sony TA-88 Been a while since my last visit. Thought I would use my old Sony as a PC CD amplifier. Last night I left it switched on and was awakened by what sounded like the cats were smashing up the catflap. I turned it on the next day and it sounds just the same. Left channel was causing the noise with the right channel still working. The left channel was not responding to the volume control being loud through the range. With the left speaker disconnected the right channel is working ok but with slight crackling. I have two of these amps with the last one traveling around the globe with me when I was in the Merchant Navy. I understand that some of the transistors used in these sets were not entirely up to the job. Not being very good at tracing faults, I would like to replace these suspects - if I knew what they were. Last edited by humphrey; 20th Dec 2017 at 5:43 pm.

20th Dec 2017, 6:46 pm	#2
Grubhead Heptode Join Date: Dec 2016 Location: Sheffield, South Yorkshire, UK. Posts: 539	Re: Sony TA-88 When you have one channel playing up then I always compare readings and just looking at them to see if there is any difference. As both channels use the same parts. You just identify which channel is which. You can't really go on what might cause a problem, because electronics don't behave like that. The big trouble makers might be working fine in your model. The ones that don't normally cause the problem could be the culprits.

21st Dec 2017, 7:26 am	#3
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,670	Re: Sony TA-88 I know the amps you mean, had a few friends had these back in the 80's, they were popular in bedsits. Service manual available here - https://www.hifiengine.com/manual_li...ny/ta-88.shtml Andy. __________________ Curiosity hasn't killed this cat...so far.

21st Dec 2017, 11:21 am	#4
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: Sony TA-88 Is an oscilloscope and signal generator any use here as although the voltages on the schematic are showing normal, it does not account for the noise on the left channel. It will be nice to use those items of equipment that have hardly been used. Last edited by humphrey; 21st Dec 2017 at 11:40 am.

21st Dec 2017, 12:51 pm	#5
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: Sony TA-88 It might be worth mentioning that that the unit is pre modification with the 315ma fuses but the resistors are according to the mod and appear to be original. Last edited by humphrey; 21st Dec 2017 at 1:08 pm.

21st Dec 2017, 3:36 pm	#6
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Sony TA-88 The Sony TA-88 has some design problems. See this thread, and especially posting #6: https://www.vintage-radio.net/forum/...highlight=ta88 Regards, Peter

21st Dec 2017, 7:10 pm	#7
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: Sony TA-88 So far I have not found any deviations from the schematics. However I have another TA88 that has no output at all. There are some odd voltages on a couple of transistors. They are Q101 and Q102 2SC631A and 2SA704. Are equivalents available?

22nd Dec 2017, 5:55 pm	#8
orbanp1 Heptode Join Date: Nov 2009 Location: London, Ontario, Canada Posts: 675	Re: Sony TA-88 There are fuses at the speaker outputs, do check those. Also check the rail voltages. If the speaker fuse was blown, do measure the DC output voltage without any input signal before you attach the speaker to it, the DC output voltage should not be more than a few 10mV! If it is significantly more, then probably the final and/or driver transistors are blown. Q101 and Q102 are part of the RIAA pre-amp for the phono input, if that is the only fault, then the amp should still work OK with the other inputs, like "tuner", and "aux". Do a search for low noise audio bjt transistors, or go to the diyAudio.com, solid-state subforum, this has been discussed there ad nauseam. Good luck, Peter

23rd Dec 2017, 11:59 am	#9
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: Sony TA-88 I just got my dead set going on one channel with no noise. At least I can compare them. I had to replace a crusty old 100mF cap in the power supply. I am thinking that I should really replace all the e caps because of their age. I could not find any dodgy transistors. Last edited by humphrey; 23rd Dec 2017 at 12:06 pm.

13th Jan 2018, 3:26 pm	#10
humphrey Retired Dormant Member Join Date: Aug 2008 Location: Bellac, 87. France. Posts: 357	Re: Sony TA-88 Changed all the E caps and it now works fine with no crackles either. Now to get the second one done. Luckily all the transistors were ok.