Macintosh Classic revival tips?

[crazyfrog]

Any tips for reviving a Macintosh classic?
I just bought this with a bag, external drive, keyboard and mouse but it doesn’t power on at all completely dead.
Using a thermal camera on the analog board there’s zero activity on the D.C. side or crt side. I’ve assumed the issue is the common internet explanation of the tda4605 or mosfet so have ordered replacements with the mosfet testing fine in my component tester.

As maintenance I’ve also recapped the analog board. These all tested fine in ESR and capacity there was liquid in this area but no real sign of these being bad.

I’ve also recapped the logic board with tantalum caps and a 1uf 50v ceramic(I had 1 and they’re expensive to order in tantalum). The condition of these was terrible no leaks but the readings were reduced capacity with esr in kohms(bad).

 

[imactheknife]

If your sound doesnt work you might have to pull sound chip off. Both my classic boards had no sound. If you had bad cap goo, check any other ic chip with nasty looking legs too

 

[crazyfrog]

That’s all a bit imprecise. I just received a replacement tda4605 so have fitted that and got a ticking noise I think from the speaker.
just tested the board hoping everything would light up under the thermal camera and it’s now making a ticking noise, I don’t know if that’s normal

7 October 2022

youtube.com

There’s voltage on the caps now I found 12.6v, 7.3v, 3v and 3.2v so haven’t found a 5v and don’t know what the voltages are meant to be.

dp3 is at 1.36v, dp4 is jumping between 9.54v-9.63v and dp1 at 12.44v

I’ll look again after tea.

 

[joshc]

These are not designed to be used without load, test again with everything fully hooked up.

The way to test the voltages is at the floppy port with the machine turned on.

 

[crazyfrog]

Thats unusual for a switching power supply.
For the sake of a few days wait to when I can go to the component shop I'll leave it till then so I can replace dp3 and dp4 with new 1n4148 and octocoupler with a new cny17-3 as it seems a terrible idea to leave these and risk damaging the crt.

 

[crazyfrog]

Working now I still need to do a bit more but it’s all up from here. The hard drive is working but stalled at the ‘welcome to Macintosh’ screen on first boot and is quite loud.
I’ve swapped out the original fan for a Silverstone 60mm with a low noise adapter(I may remove that)

As there was initially no D.C. voltage I replaced the mosfet with a IRFBC40APBF, controller with a ebay special tda4605 and octocoupler with CNY17-3 and signal diodes with 1N148. By the time I got to cp4 and cp5 my component tester had popped and broken so I replaced these with general purpose caps which weren’t 30 years

Using a component tester most the capacitors tested fine with the larger dc caps having some leakage I replaced the larger caps.

logic board caps were replaced with kemet tantalum as per recap a mac.

This week I’ll be fitting a bluescsi once I get a molex to floppy adaptor and likely adding a silent rear exhaust fan with the theory it will boost the life of the crt.

 

[alexGS]

Nice work, I’m similarly confronted with one of these. I wonder how all those parts can be faulty at once… Does the MOSFET fail and take out the TDA4605 with it, or was it just the 1N4148 diodes all along?

If they all need replacing then it will take me weeks of separate orders. I laughed when one supplier’s website said the MOSFET was backordered until 2024, but would deliver in one business day with a 20% discount (welcome to 2022)…

 

[crazyfrog]

Nice work, I’m similarly confronted with one of these. I wonder how all those parts can be faulty at once… Does the MOSFET fail and take out the TDA4605 with it, or was it just the 1N4148 diodes all along?

If they all need replacing then it will take me weeks of separate orders. I laughed when one supplier’s website said the MOSFET was backordered until 2024, but would deliver in one business day with a 20% discount (welcome to 2022)…

Mosfets tend to be the part of a power supply that fail in general. I replaced the lot as I never want to take that classic apart again to work on the analog board.
I couldnt find tda4605 it seems to be mega discontinued instead I got a china special off ebay locally(though I could have gotten from aliexpress) with the correct chip markings, the mosfet was equivalent and the diodes are general purpose parts anyway.

 

[crazyfrog]

File is called HD0-OpenRetroSCSI-7.1.hda and log reads

BlueSCSI <-> SD - https://github.com/erichelgeson/BlueSCSI
VER: 1.1-20220917
DEBUG:0 SDFAT_FILE_TYPE:3
SdFat version: 2.2.0
Sd Format: exFAT
SPI speed: 50Mhz
SdFat Max FileName Length: 64
Initialized SD Card - let's go!
Sd MID:3 OID:SD
Sd Name:SC128
Sd Date:1/2020
Sd Serial:269861749
HD0-OpenRetroSCSI-7.1.hda - bad SCSI LUN in filename, Using default LUN ID 0
- HD0-OpenRetroSCSI-7.1.hda HDD / 524288000bytes / 512000KiB / 500MiB
ID:LUN0:
0: 512:
1:----:
2:----:
3:----:
4:----:
5:----:
6:----:
Finished initialization of SCSI Devices - Entering main loop.

 

[jshardin]

Mosfets tend to be the part of a power supply that fail in general. I replaced the lot as I never want to take that classic apart again to work on the analog board.
I couldnt find tda4605 it seems to be mega discontinued instead I got a china special off ebay locally(though I could have gotten from aliexpress) with the correct chip markings, the mosfet was equivalent and the diodes are general purpose parts anyway.

Sorry, I read this and laughed out loud as you must have been reading my mind.. I've just finished restoring 4 classics and I swear I will never touch another one of those analog boards again.

 

[crazyfrog]

I replaced everything I thought necessary had the main fuse blow on my second classic and found a blown diode and rifa cap, replaced the diode and removed the rifa but no dc voltage.
I’ve not touched it since start of December still angry and can’t be arsed for now.