Decca SRG899 filter cap gone bad?

[al_kaholik]

Originally Posted by Robint 47

Sorry I am not able to understand your voltage readings on this amp. To this end I have a copy of the Decca 613 amp circuit (Decca module ass 6000) which for an email address I will supply. Before I am jumped on I have offered this to the site but no one responds and tells me where to send it? I feel this could be one of the few remaining copies.

You can then post the readings which are on the data and post on to the site not to me, i have some thoughts where your problem lies first let's see the data then do you have access to a meter capable of reading DC current, oscilloscope and an audio generator. I can then tailor my reply accordingly.

Robin

Hi Robin, many thanks for the offer, I will send you a PM shortly with my email address. Hopefully this will help along with things.

Unfortunately I've made no progress this weekend, other bits and pieces have taken priority.

Al

[al_kaholik]

I'd like to publically put a big shout out to Robint 47 who has come through with the wiring diagrams. Been a little short of time - even to respond to his email or even look in detail at the diagrams, but thank you.

I will upload them here in the thread shortly and hopefully it will be a great help in diagnosing the issues

[al_kaholik]

Finally had a few minutes to update on this. I have uploaded the diagrams kindly provided by robint47 which are attached and have tested the voltage at each transistor as attached. All of the heat sunk transistors are TIP31 except T107 which is R2447 - unfortunately I shorted this whilst testing and now there is no sound whatsoever from the left channel - no hum, so presumed dead - this happened as the very last (typical) test was taking place.

From the measurements T108 looks suspect, and 107 will need replacing irrespective.

There is also the possibility that I have recorded the wrong measures for Emitter and Collector on T103/203 however if so, they are consistent

Al

[al_kaholik]

Anybody have any thoughts on this?

[Uncle Bulgaria]

The circuit diagram has been compressed by the forum software so from here it's too small to be legible. Can you provide a link to Dropbox or similar, or provide a format that isn't reduced in size to the same extent? In the 'advanced' reply box there's an indication of the maximum file sizes for different formats, and sometimes you'll be able to get a PDF, say, at a good enough B&W resolution that it works, otherwise you'll have to do a link to an externally shared file.

It looks like you've got your pins muddled, but as you say they're consistent.

If no-one else chimes in I can try muddling through the circuit diagram with you if you can get a higher resolution one uploaded.

[kirstyd]

just a thought but i had the same problem with one of these .the hum was caused by an earth loop that i had accidently caused myself when i undid the nuts holding the rotary controls in place .there is a clear plastic washer that is fitted before the bolt .Also another fault was caused by a cracked plastic block that the FM tuner is mounted on .the cracked block was causing the same fault .The post is still on here take a look at it might be of some help

[neil29]

Someone else also had a problem as well which turned out to be picking up mains hum from near the switch. and i had one years ago which had the same problem. like kirsty says it might not be the fault but worth a check nonetheless.

Cheers
Neil.

[al_kaholik]

I will have a look, thanks both.

Uncle Bulgaria - very kind, thank you. I have unfortunately had a health issue which has stopped me coming on here until today. I will try to get it uploaded again later today

[al_kaholik]

Finally back after a long hiatus on this. I've uploaded the circuits previously discussed onto Flickr so hopefully they will be a bit easier to read. I haven't even touched the unit in months, but hopefully can have another burst of activity, health permitting

https://********/p/2kCVVfF

https://********/p/2kCWtxh

https://********/p/2kCVVgs