September 24, 2021 - 07:51 pm|
|Hello! First off, thanks so much for the work you've put into creating and maintaing this site. Its been super helpful in giving me the confidence (possibly misplaced) to tackle my own effort at rehabilitating. I don't have a lot of experience in trouble shooting so apologies if I provide too much information, but I do have a couple questions at the end if you just wanna skip to those.|
I picked up a busted 3070 at the goodwill (wouldn't run, lots of transistors shorted, light blown out, oddly fuses seemed to be in good shape?) and got to work ripping out caps, testing components out of circuit, cheking for correct placement and continuity with regards to wiring, etc. All the steps I thought might help give me the best shot at minimal troubleshooting once I had all the mods completed.
I discovered later on (after much frustration and furrowed brows trying to account for some discrepancies in the schematic) that my particular unit had already been modified to some extent, so where I noticed any mods I attempted to find matching parts for the original design. The individual had also made some very odd (in my amateur opinion) choices, but I won't go into those.
After following your suggested mods (all except tweaks to tone control due to limited testing equipment) I turned it on this week for the first time and am now stumped. The signal (through both aux and phono jacks) appears to be making it through the unit and out the speakers (and headphone jack) but the volume level is very very low - when the volume knob is cranked all the way you can just make out the music. There is hardly any hum though and it sounds pretty good overall, just at a very low level. I have tested all the voltages provided at the given points on the schematic and they all match within 5-10% of the expected value with a bit higher voltage near the output PCB (which I figured was accounted for by the new transistors). Additionally, the expected voltage is present on R12 and I was able to adjust the trim pot as stated in the guide.
QUESTIONs FOR FEEDBACK:
1) I was unable to find replacements for the listed diodes for the output transistors and after some studying and speaking with an individual at the local shop, he recommended replacing CR1, CR2, CR3, and CR4 with 1N4007s. He didn't seem too confident in this area though. Is that a suitable sub for the diodes? They are certainly way above the necessary voltage level (he said 4003s would work too but all they had on hand were the 4007s) but its one of the few areas where I wasn't able to get 1:1 replacements.
2) I have cleaned all the switches and pots with q-tips and 99% iso but wasn't sure if there is more to be done to constitute a proper cleaning of this area and could it be contributing to the issue?
3) In your suggested mods you mentioned changing out the bootstrap cap of C302 to a different value, but it appears that might have been talking about C303, given my limited understanding of bootstraps and how they work. Is that a typo? I went ahead and put the replacement cap into C303.
"Increase the bootstrap caps (C302–both channels). Presently 100uF, 25V, you could try 470uF, 35V, TVX1V471MCD, $1.05 at Mouser. Should fit."
Thanks again! Any feedback you could offer (or anyone else coming across the site) would be really appreciated.
June 13, 2021 - 06:54 am|
November 09, 2020 - 07:37 am|
|Hi Fred, It's kind of you to post. Will be happy to help if you have any questions. Let us know how it goes. Best wishes for your restoration! |
November 08, 2020 - 10:57 pm|
|Thanks for posing this information. It gives me the confidence to begin restoring my 3070. |
October 14, 2020 - 06:08 pm|
|Hi Jake, Yes, that fuse will be fine and yes, I'll send you an email. At this point, it probably makes sense to take it off the public comments anyway, in case we get into the minutia of debugging. |
October 14, 2020 - 09:29 am|
|Hi Steve. I checked the fuses and they are indeed blown so yea looks like I shorted things with those transistors.|
Glad that I can get the insulators still.
Is this the right fuse? I measured the fuse and this appears to be correct.
Mouser part# 576-0312002.MXP
Thanks for your help. Can you email me at j b r i t s c h @ gmail.com?