Blown fuse suggestions

[crazyfrog]

So I’ve bought a Macintosh classic II which powered to white bars and decided to go through recapping the logic board with tantalum caps as well as analogue board with low esr caps using recapamac.com.au/ as reference as well as dp3 and dp4. After the work I powered the macintosh and got the same white bars the first time I powered it and no screen output on second boot.

At this point I measured the logic board power connector pins and got the following voltages
1. 12v 12.13v
2. 5.07v
3. 5.07v
4. 0.23v
5. 3.32
6. 0v
7. 0v
8. -11.85v
9. 2.42v
10. 0v
11. 0v
12. 0v

I've worked on a macintosh classic previously and ordered a set of tda4605 chips and received tda4605-3 from aliexpress. After replacing tda4605-3 it powered for a few seconds with display then the main glass fuse blew and I later found a short on dp5 diode.

At this point I'm looking at replacing the mosfet, tda4605 from previous source and dp5 with another diode as well as qp1 with another octocoupler(as Philips CNY17g-3 doesnt seem to be available).

 

[bibilit]

At this point I'm looking at replacing the mosfet

Probably your issue here for a blowing fuse.

later found a short on dp5 diode.

Contaminated by cap goo...

 

[crazyfrog]

Probably your issue here for a blowing fuse.



Contaminated by cap goo...

Possibly but theres very little left on the board now. I'm just going about sourcing equivalent parts for the power supply but I'm more concerned about the bars that havent gone away at all with the logic board, analog board recap.

 

[dochilli]

Could be a RAM or ROM problem. Did you clean and reseat them?
Do you have known working RAM?

 

[crazyfrog]

I’ve not cleaned this as the board was quite clean to begin with.

perhaps, I don’t know what to do with the rom chips, but I’ve tried reseating the ram modules and no difference. Apparently there’s ram on the logic board so should boot without. There’s also 2 jumpers on the logic board that aren’t terminated and I don’t know what they’re for.

 

[bibilit]

Apparently there’s ram on the logic board so should boot without. There’s also 2 jumpers on the logic board that aren’t terminated and I don’t know what they’re for.

Yes should boot with the on-board ram only.

Rom is never known to be faulty or heavily contaminated on the Classic, don't remember about the jumpers, never used IIRC

 

[joshc]

Can you post some photos of your logic board please?

 

[crazyfrog]

Can you post some photos of your logic board please?

See post 1. If you gave me more info on what you think could be the issue I could certainly check/photograph that.

 

[bibilit]

I will personally try to remove the Egret (U10 chip on the upper right corner) clean underneath and solder it back again.

That chip is near a bunch of caps and often contaminated by cap goo, i have repaired a lot of boards by simply lifting and cleaning...

this chip is related to the boot process, and near impossible to clean without removal.

The jumpers were probably provided for a Rom upgrade that never was made available, never seen any jumper there.

 

[joshc]

Oops sorry missed that pic. Basically +1 to what @bibilit said. The legs of the Egret chip are dirty and need to be cleaned. Also you should clean all other chips near caps thoroughly.

 

[crazyfrog]

I will personally try to remove the Egret (U10 chip on the upper right corner) clean underneath and solder it back again.

That chip is near a bunch of caps and often contaminated by cap goo, i have repaired a lot of boards by simply lifting and cleaning...

this chip is related to the boot process, and near impossible to clean without removal.

The jumpers were probably provided for a Rom upgrade that never was made available, never seen any jumper there.

Oops sorry missed that pic. Basically +1 to what @bibilit said. The legs of the Egret chip are dirty and need to be cleaned. Also you should clean all other chips near caps thoroughly.

Thanks for the advice if it’s a bad area I’ll definitely go through cleaning with alcohol and checking the traces best I can but I won’t removing that chip with my 858d hot air station for many reasons including it’s not a bga chip.

 

[bibilit]

Thanks for the advice if it’s a bad area I’ll definitely go through cleaning with alcohol and checking the traces best I can but I won’t removing that chip with my 858d hot air station for many reasons including it’s not a bga chip.

As said, near impossible to clean without removing, goo is conductive and the chip is probably shorted.
Already tried all sort of tricks trying to leave the chip unmolested, but only removing, cleaning both the legs and traces solved the issue.

Common issue on the Classic II / CC / LC..

 

[crazyfrog]

As said, near impossible to clean without removing, goo is conductive and the chip is probably shorted.
Already tried all sort of tricks trying to leave the chip unmolested, but only removing, cleaning both the legs and traces solved the issue.

Common issue on the Classic II / CC / LC..

I appreciate the comment but I'm not that far in yet. Currently struggling to get the analog board back and working. I've just replaced the mosfet, octocoupler, fuse, dp5 diode and another TDA4605 but the power supply isn't working theres no power after the transformer. I'm currently blaming the aliexpress tda4605-3 so I'm ordering a tda4605 from an ebay source I've used previously.

https://www.aliexpress.com/item/32826596427.html?spm=a2g0o.order_list.0.0.b8e61802eHtyw0

Heres links to the parts used

https://cpc.farnell.com/stmicroelectronics/stp6nk60zfp/mosfet-n-to-220fp/dp/SC16906?CMP=TREML007-005

https://cpc.farnell.com/vishay/cny17-3/optocoupler-transistor-o-p/dp/SC12283?CMP=TREML007-005

https://cpc.farnell.com/eaton-bussmann-series/s506-3-15-r/fuse-time-delay-20mm-3-15a/dp/FF01275

https://cpc.farnell.com/vishay/uf5404/si-d-400v-3a/dp/SCUF5404?CMP=TREML007-005

 

[crazyfrog]

Still more issues its now chirping when powered every second or so, just put in a tda4605 from a source I've bought from before. 1.2v and 0.53v on 12v and 5v

 

[crazyfrog]

Just had another component blow cp38 refa capacitor. I dont think this can cause the no power issue I'm having so I'll carry on looking
Heres a snippet of the circuit diagram I found in case anyone knows different