Need Help with my 82905 Printer - IL Version

[jebem]

(02-27-2016 02:01 PM)Michael Fehlhammer Wrote:  The printer is a recognized device, it's answer to DEVID$ is "HP82905B".
Meanwhile I swapped the IL PCB with the known-good one of my second printer ( which differs only in the input voltage, it's the US version). I also assured that the chips are firmly seated in their sockets. But: No reaction from the printer.
So I am sure that the printer mainboard is faulty. Hmm, I am afraid there isn't much that can be done?
I will try to get an Epson FX 80, maybe the main board is identical, but these printers are also rare meanwhile. Currently there is not a single FX-80 on Ebay.
Well, since I have got a working and a non-working 82905B:
How much effort would it be for an electronics expert to track down the faulty component, by comparing the two? And then - will there be a replacement part available? Is it more likely that common simple components like capacitors fail, or proprietary integrated circuits?
Or should I surrender? :-(

Paul mention that it is based on the once popular Epson MX-80 (also here).
I have done firmware modifications (EPROM based) on these machines in their time (specially character set localization) but I have not kept any documentation.

From your diagnosis results, we can assume that the printer main board is faulty at the parallel I/O interface.
This was a common failure if I remember it well.

I found this manual that may help as it contains the schematics.

I suppose the IC's supporting the parallel I/O are faluty and need need to be replaced, assuming the correct 5VDC power supply voltage are present at these IC's.

This parallel interface, also called Centronics in my time, uses 8 non balanced data lines (bit 0 to 7) operating at 5VDC TTL connected to the 8155 40-pin IC marked as 8B in the schematics.
The additional Centronics protocol is handled by discrete very common easy to find 14 or 16-pin TTL ICs marked as 2E (74LS00 2-in-nand-gate), 3C (74LS04 inverter) and 3E (HD14093 2-in-nand-schmit).

If you can use a multi-meter set to Volts and are willing to apply outlet energy to both printers (the working and non working ones) while the covers are opened (do this at your own risk):

- Check the +5VDC voltage between ground and the Integrated Circuits power supply pins.

- If the voltages are correct, then I would replace those parallel I/O IC's (one at a time).

- If not, check the power supply.
Sometimes these PCB's uses small fuses that do not look like fuses at all - They look like small radial capacitors but most probably they are marked in the PCB as fuses.
Check for burnt resistors as well - many times they are easy to spot by visual inspection, or else use a continuity (ohms) checker.